Commit Graph

399 Commits

Author SHA1 Message Date
Paul E. McKenney 1f3ebc8253 rcu: Restore barrier() to rcu_read_lock() and rcu_read_unlock()
Commit bb73c52bad ("rcu: Don't disable preemption for Tiny and Tree
RCU readers") removed the barrier() calls from rcu_read_lock() and
rcu_write_lock() in CONFIG_PREEMPT=n&&CONFIG_PREEMPT_COUNT=n kernels.
Within RCU, this commit was OK, but it failed to account for things like
get_user() that can pagefault and that can be reordered by the compiler.
Lack of the barrier() calls in rcu_read_lock() and rcu_read_unlock()
can cause these page faults to migrate into RCU read-side critical
sections, which in CONFIG_PREEMPT=n kernels could result in too-short
grace periods and arbitrary misbehavior.  Please see commit 386afc9114
("spinlocks and preemption points need to be at least compiler barriers")
and Linus's commit 66be4e66a7 ("rcu: locking and unlocking need to
always be at least barriers"), this last of which restores the barrier()
call to both rcu_read_lock() and rcu_read_unlock().

This commit removes barrier() calls that are no longer needed given that
the addition of them in Linus's commit noted above.  The combination of
this commit and Linus's commit effectively reverts commit bb73c52bad
("rcu: Don't disable preemption for Tiny and Tree RCU readers").

Reported-by: Herbert Xu <herbert@gondor.apana.org.au>
Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
[ paulmck: Fix embarrassing typo located by Alan Stern. ]
2019-08-01 14:05:51 -07:00
Mauro Carvalho Chehab bff9e34c67 docs: fix broken doc references due to renames
Some files got renamed but probably due to some merge conflicts,
a few references still point to the old locations.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
2019-07-17 06:57:51 -03:00
Linus Torvalds e9a83bd232 It's been a relatively busy cycle for docs:
- A fair pile of RST conversions, many from Mauro.  These create more
    than the usual number of simple but annoying merge conflicts with other
    trees, unfortunately.  He has a lot more of these waiting on the wings
    that, I think, will go to you directly later on.
 
  - A new document on how to use merges and rebases in kernel repos, and one
    on Spectre vulnerabilities.
 
  - Various improvements to the build system, including automatic markup of
    function() references because some people, for reasons I will never
    understand, were of the opinion that :c:func:``function()`` is
    unattractive and not fun to type.
 
  - We now recommend using sphinx 1.7, but still support back to 1.4.
 
  - Lots of smaller improvements, warning fixes, typo fixes, etc.
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Merge tag 'docs-5.3' of git://git.lwn.net/linux

Pull Documentation updates from Jonathan Corbet:
 "It's been a relatively busy cycle for docs:

   - A fair pile of RST conversions, many from Mauro. These create more
     than the usual number of simple but annoying merge conflicts with
     other trees, unfortunately. He has a lot more of these waiting on
     the wings that, I think, will go to you directly later on.

   - A new document on how to use merges and rebases in kernel repos,
     and one on Spectre vulnerabilities.

   - Various improvements to the build system, including automatic
     markup of function() references because some people, for reasons I
     will never understand, were of the opinion that
     :c:func:``function()`` is unattractive and not fun to type.

   - We now recommend using sphinx 1.7, but still support back to 1.4.

   - Lots of smaller improvements, warning fixes, typo fixes, etc"

* tag 'docs-5.3' of git://git.lwn.net/linux: (129 commits)
  docs: automarkup.py: ignore exceptions when seeking for xrefs
  docs: Move binderfs to admin-guide
  Disable Sphinx SmartyPants in HTML output
  doc: RCU callback locks need only _bh, not necessarily _irq
  docs: format kernel-parameters -- as code
  Doc : doc-guide : Fix a typo
  platform: x86: get rid of a non-existent document
  Add the RCU docs to the core-api manual
  Documentation: RCU: Add TOC tree hooks
  Documentation: RCU: Rename txt files to rst
  Documentation: RCU: Convert RCU UP systems to reST
  Documentation: RCU: Convert RCU linked list to reST
  Documentation: RCU: Convert RCU basic concepts to reST
  docs: filesystems: Remove uneeded .rst extension on toctables
  scripts/sphinx-pre-install: fix out-of-tree build
  docs: zh_CN: submitting-drivers.rst: Remove a duplicated Documentation/
  Documentation: PGP: update for newer HW devices
  Documentation: Add section about CPU vulnerabilities for Spectre
  Documentation: platform: Delete x86-laptop-drivers.txt
  docs: Note that :c:func: should no longer be used
  ...
2019-07-09 12:34:26 -07:00
Jiunn Chang acb6258acc doc: RCU callback locks need only _bh, not necessarily _irq
The UP.rst file calls for locks acquired within RCU callback functions
to use _irq variants (spin_lock_irqsave() or similar), which does work,
but can be overkill.  This commit therefore instead calls for _bh variants
(spin_lock_bh() or similar), while noting that _irq does work.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Jiunn Chang <c0d1n61at3@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2019-06-28 09:10:40 -06:00
Jiunn Chang c0e679b4a1 Documentation: RCU: Add TOC tree hooks
Add TOC tree hooks for:
  - rcu
  - listRCU
  - UP

Signed-off-by: Jiunn Chang <c0d1n61at3@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2019-06-27 08:19:08 -06:00
Jiunn Chang f93a3e4e87 Documentation: RCU: Rename txt files to rst
Rename the following files to reST:
  - rcu.txt
  - listRCU.txt
  - UP.txt

Signed-off-by: Jiunn Chang <c0d1n61at3@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2019-06-27 08:19:02 -06:00
Jiunn Chang 2a5b0c841a Documentation: RCU: Convert RCU UP systems to reST
RCU UP systems reST markup.

Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Jiunn Chang <c0d1n61at3@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2019-06-27 08:18:51 -06:00
Jiunn Chang 9422dc24df Documentation: RCU: Convert RCU linked list to reST
RCU linked list reST markup.

Signed-off-by: Jiunn Chang <c0d1n61at3@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2019-06-27 08:18:41 -06:00
Jiunn Chang a9f0969cd7 Documentation: RCU: Convert RCU basic concepts to reST
RCU basic concepts reST markup.

Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Jiunn Chang <c0d1n61at3@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2019-06-27 08:18:17 -06:00
Paul E. McKenney 11ca7a9d54 Merge branches 'consolidate.2019.05.28a', 'doc.2019.05.28a', 'fixes.2019.06.13a', 'srcu.2019.05.28a', 'sync.2019.05.28a' and 'torture.2019.05.28a' into HEAD
consolidate.2019.05.28a: RCU flavor consolidation cleanups and optmizations.
doc.2019.05.28a: Documentation updates.
fixes.2019.06.13a: Miscellaneous fixes.
srcu.2019.05.28a: SRCU updates.
sync.2019.05.28a: RCU-sync flavor consolidation.
torture.2019.05.28a: Torture-test updates.
2019-06-19 09:21:46 -07:00
Andrea Parri 9129b017b5 rcu: Don't return a value from rcu_assign_pointer()
Quoting Paul [1]:

  "Given that a quick (and perhaps error-prone) search of the uses
   of rcu_assign_pointer() in v5.1 didn't find a single use of the
   return value, let's please instead change the documentation and
   implementation to eliminate the return value."

[1] https://lkml.kernel.org/r/20190523135013.GL28207@linux.ibm.com

Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: rcu@vger.kernel.org
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Sasha Levin <sashal@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-06-13 15:38:34 -07:00
Zhenzhong Duan 588759a391 doc: Fixup definition of rcupdate.rcu_task_stall_timeout
A positive value of rcupdate.rcu_task_stall_timeout is an interval
in seconds rather than jiffies.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-05-28 09:02:16 -07:00
Joel Fernandes (Google) de1dbcee43 doc/rcuref: Document real world examples in kernel
Document similar real world examples in the kernel corresponding to the
second and third code snippets. Also correct an issue in
release_referenced() in the code snippet example.

Cc: oleg@redhat.com
Cc: jannh@google.com
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Do a bit of wordsmithing. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-05-28 09:02:16 -07:00
Paul E. McKenney 884b429ae6 doc: Fix typos and otherwise modernize checklist.txt
This commit fixes some issues with Documentation/RCU/checklist.txt.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-03-26 14:37:06 -07:00
Paul E. McKenney d1b493bbe1 doc: Describe choice of rcu_dereference() APIs and __rcu usage
Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-03-26 14:37:06 -07:00
Tycho Andersen 0fa201d161 doc: Repair some whitespace damage
A diagram in whatisRCU.txt has space character before tabs.  This commit
therefore makes this diagram consistent with elsewhere in the document:
Use one leading tab, followed by spaces for any additional whitespace
required.

Signed-off-by: Tycho Andersen <tycho@tycho.ws>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-03-26 14:37:06 -07:00
Paul E. McKenney 4fea6ef0b2 doc: Remove obsolete RCU update functions from RCU documentation
Now that synchronize_rcu_bh, synchronize_rcu_bh_expedited, call_rcu_bh,
rcu_barrier_bh, synchronize_sched, synchronize_sched_expedited,
call_rcu_sched, rcu_barrier_sched, get_state_synchronize_sched,
and cond_synchronize_sched are obsolete, let's remove them from the
documentation aside from a small historical section.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-03-26 14:37:06 -07:00
Linus Torvalds 1a29e85750 A fairly routine cycle for docs - lots of typo fixes, some new documents,
and more translations.  There's also some LICENSES adjustments from
 Thomas.
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Merge tag 'docs-5.1' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "A fairly routine cycle for docs - lots of typo fixes, some new
  documents, and more translations. There's also some LICENSES
  adjustments from Thomas"

* tag 'docs-5.1' of git://git.lwn.net/linux: (74 commits)
  docs: Bring some order to filesystem documentation
  Documentation/locking/lockdep: Drop last two chars of sample states
  doc: rcu: Suspicious RCU usage is a warning
  docs: driver-api: iio: fix errors in documentation
  Documentation/process/howto: Update for 4.x -> 5.x versioning
  docs: Explicitly state that the 'Fixes:' tag shouldn't split lines
  doc: security: Add kern-doc for lsm_hooks.h
  doc: sctp: Merge and clean up rst files
  Docs: Correct /proc/stat path
  scripts/spdxcheck.py: fix C++ comment style detection
  doc: fix typos in license-rules.rst
  Documentation: fix admin-guide/README.rst minimum gcc version requirement
  doc: process: complete removal of info about -git patches
  doc: translations: sync translations 'remove info about -git patches'
  perf-security: wrap paragraphs on 72 columns
  perf-security: elaborate on perf_events/Perf privileged users
  perf-security: document collected perf_events/Perf data categories
  perf-security: document perf_events/Perf resource control
  sysfs.txt: add note on available attribute macros
  docs: kernel-doc: typo "if ... if" -> "if ... is"
  ...
2019-03-09 09:56:17 -08:00
Geert Uytterhoeven 866d65b9d7 Documentation/locking/lockdep: Drop last two chars of sample states
Since the removal of FS_RECLAIM annotations, lockdep states contain four
characters, not six.

Fixes: e5684bbfc3 ("Documentation/locking/lockdep: Update info about states")
Fixes: d92a8cfcb3 ("locking/lockdep: Rework FS_RECLAIM annotation")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2019-03-04 12:55:18 -07:00
Geert Uytterhoeven 6cd43851f8 doc: rcu: Suspicious RCU usage is a warning
Suspicious RCU usage messages are reported as warnings.

Fixes: a5dd63efda ("lockdep: Use "WARNING" tag on lockdep splats")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Paul E. McKenney <paulmck@linux.ibm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2019-03-04 12:53:15 -07:00
Paul E. McKenney e7ffb4eb9a Merge branches 'doc.2019.01.26a', 'fixes.2019.01.26a', 'sil.2019.01.26a', 'spdx.2019.02.09a', 'srcu.2019.01.26a' and 'torture.2019.01.26a' into HEAD
doc.2019.01.26a:  Documentation updates.
fixes.2019.01.26a:  Miscellaneous fixes.
sil.2019.01.26a:  Removal of a few more spin_is_locked() instances.
spdx.2019.02.09a:  Add SPDX identifiers to RCU files
srcu.2019.01.26a:  SRCU updates.
torture.2019.01.26a: Torture-test updates.
2019-02-09 08:47:52 -08:00
Junchang Wang 6684880a8b RCU/torture.txt: Remove section MODULE PARAMETERS
The supported module parameters are detailed in both RCU/torture.txt and
admin-guide/kernel-parameters.txt, and the latter is actively maintained.
So this patch removes section MODULE PARAMETERS in torture.txt and
adds a reference to the information in kernel-parameters.txt.

Signed-off-by: Junchang Wang <junchangwang@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
[ paulmck: Add search string. ]
2019-01-25 15:37:14 -08:00
Paul E. McKenney fb60e533be rcu: Rename rcu_process_callbacks() to rcu_core() for Tree RCU
Although the name rcu_process_callbacks() still makes sense for Tiny
RCU, where most of what it does is invoke callbacks, it no longer makes
much sense for Tree RCU, especially given that the actually callback
invocation is relegated to rcu_do_batch(), or, for no-CBs CPUs, to the
rcuo kthreads.  Especially in the latter case, rcu_process_callbacks()
has very little to do with actual callbacks.  A better description of
this function is that it performs RCU's core processing.

This commit therefore changes the name of Tree RCU's rcu_process_callbacks()
function to rcu_core(), which also has the virtue of being consistent with
the existing invoke_rcu_core() function.

While in the area, the header comment is reworked.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-01-25 15:35:22 -08:00
Paul E. McKenney c98cac603f rcu: Rename rcu_check_callbacks() to rcu_sched_clock_irq()
The name rcu_check_callbacks() arguably made sense back in the early
2000s when RCU was quite a bit simpler than it is today, but it has
become quite misleading, especially with the advent of dyntick-idle
and NO_HZ_FULL.  The rcu_check_callbacks() function is RCU's hook into
the scheduling-clock interrupt, and is now but one of many ways that
callbacks get promoted to invocable state.

This commit therefore changes the name to rcu_sched_clock_irq(),
which is the same number of characters and clearly indicates this
function's relation to the rest of the Linux kernel.  In addition, for
the sake of consistency, rcu_flavor_check_callbacks() is also renamed
to rcu_flavor_sched_clock_irq().

While in the area, the header comments for both functions are reworked.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-01-25 15:35:21 -08:00
Junchang Wang 87d1779dc4 doc: Fix outdated links
Fix outdated links in whatisRCU.txt.

Signed-off-by: Junchang Wang <junchangwang@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-01-25 15:34:18 -08:00
Paul E. McKenney 6efebf8499 doc: CPU-hotplug notifiers cannot invoke synchronize_srcu() or srcu_barrier()
SRCU's synchronize_srcu() may not be invoked from CPU-hotplug notifiers,
due to the fact that SRCU grace periods make use of timers and the
possibility of timers being temporarily stranded on the outgoing CPU.
This stranding of timers means that timers posted to the outgoing CPU
will not fire until late in the CPU-hotplug process.  The problem is
that if a notifier is waiting on an SRCU grace period, that grace period
is waiting on a timer, and that timer is stranded on the outgoing CPU,
then the notifier will never be awakened, in other words, deadlock has
occurred.  This same situation of course also prohibits srcu_barrier()
from being invoked from CPU-hotplug notifiers.

This commit therefore updates the requirements to include this restriction.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-01-25 15:34:18 -08:00
Paul E. McKenney 260e1e4fd8 rcu: Discard separate per-CPU callback counts
Back when there were multiple flavors of RCU, it was necessary to
separately count lazy and non-lazy callbacks for each CPU.  These counts
were used in CONFIG_RCU_FAST_NO_HZ kernels to determine how long a newly
idle CPU should be allowed to sleep before handling its RCU callbacks.
But now that there is only one flavor, the callback counts for a given
CPU's sole rcu_data structure are the counts for that CPU.

This commit therefore removes the rcu_data structure's ->nonlazy_posted
and ->nonlazy_posted_snap fields, the rcu_idle_count_callbacks_posted()
and rcu_cpu_has_callbacks() functions, repurposes the rcu_data structure's
->all_lazy field to record the laziness state at the beginning of the
latest idle sojourn, and modifies CONFIG_RCU_FAST_NO_HZ RCU CPU stall
warnings accordingly.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-01-25 15:28:30 -08:00
Paul E. McKenney 142d106d5e rcu: Determine expedited-GP IPI handler at build time
Back when there could be multiple RCU flavors running in the same kernel
at the same time, it was necessary to specify the expedited grace-period
IPI handler at runtime.  Now that there is only one RCU flavor, the
IPI handler can be determined at build time.  There is therefore no
longer any reason for the RCU-preempt and RCU-sched IPI handlers to
have different names, nor is there any reason to pass these handlers in
function arguments and in the data structures enclosing workqueues.

This commit therefore makes all these changes, pushing the specification
of the expedited grace-period IPI handler down to the point of use.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2019-01-25 15:28:27 -08:00
Joel Fernandes (Google) 97b59370fa doc: Fix "struction" typo in RCU memory-ordering documentation
This commit replaces "struction" with the correct "structure".

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:56:25 -08:00
Joel Fernandes (Google) a78ad16c7f doc: Correct parameter in stallwarn
The stallwarn document incorrectly mentions 'fps=' instead of 'fqs='.
This commit orrects that.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:56:25 -08:00
Paul E. McKenney 97562c0181 doc: RCU scheduler spinlock rcu_read_unlock() restriction remains
Given RCU flavor consolidation, when rcu_read_unlock() is invoked with
interrupts disabled, the reporting of the corresponding quiescent state is
deferred until interrupts are re-enabled.  There was therefore some hope
that this would allow dropping the restriction against holding scheduler
spinlocks across an rcu_read_unlock() without disabling interrupts across
the entire corresponding RCU read-side critical section.  Unfortunately,
the need to quickly provide a quiescent state to expedited grace periods
sometimes requires a call to raise_softirq() during rcu_read_unlock()
execution.  Because raise_softirq() can sometimes acquire the scheduler
spinlocks, the restriction must remain in effect.  This commit therefore
updates the RCU requirements documentation accordingly.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:56:25 -08:00
Joel Fernandes (Google) 97949f0176 doc: Make listing in RCU perf/scale requirements use rcu_assign_pointer()
The code listing under this section has a quick quiz that says line
19 uses rcu_access_pointer, but the code listing itself instead uses
rcu_dereference().  This commit therefore makes the code listing match
the quick quiz.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:56:25 -08:00
Joel Fernandes (Google) 8b9df28d7f doc: Remove obsolete (non-)requirement about disabling preemption
The Requirements.html document says "Disabling Preemption Does
Not Block Grace Periods".  However this is no longer true with
the RCU consolidation.  This commit therefore removes the obsolete
(non-)requirement entirely.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:56:25 -08:00
Joel Fernandes (Google) 93eb14201f doc: Make reader aware of rcu_dereference_protected
The whatisRCU.txt document says rcu_dereference() cannot be used
outside of rcu_read_lock() protected sections.  The commit adds a
mention of rcu_dereference_protected(), so that the new reader knows
that this API can be used to avoid update-side use of rcu_read_lock()
and rcu_read_unlock().

Cc: tytso@mit.edu
Suggested-by: tytso@mit.edu
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
[ paulmck: Update wording, including further feedback from Joel. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:56:25 -08:00
Joel Fernandes (Google) 1c7d6d4411 doc: rcu: Encourage use of rcu_barrier in checklist
The checklist suggests rcu_barrier_bh() for RCU-bh and similarly for
sched, however these APIs are now implemented as rcu_barrier() itself due
to the RCU consolidation. This commit therefore corrects checklist.txt
to encourage use of the underlying rcu_barrier() API.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:56:25 -08:00
Joel Fernandes (Google) e060a03a1c doc: rcu: Remove obsolete checklist item about synchronize_rcu usage
Since the RCU mechanisms have been consolidated, the checklist item
warning that synchronize_rcu() waits only for RCU readers is obsolete.
This commit therefore removes this checklist item.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:56:25 -08:00
Joel Fernandes (Google) bc2072c9ad doc: rcu: Remove obsolete suggestion from checklist
call_rcu_bh is now implemented in terms of call_rcu, so the suggestion
to use a different API for speed benefits is not accurate anymore.
This commit updates the document accordingly.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:56:25 -08:00
Joel Fernandes (Google) 090c1685fd doc: rcu: Add more rationale for using rcu_read_lock_sched in checklist
This commit explains why rcu_read_lock_sched is better than using
preempt_disable.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:56:25 -08:00
Joel Fernandes (Google) 3398496483 doc: rcu: Update core and full API in whatisRCU
RCU consolidation effort causes the update side of the RCU API to
be consistent across all the 3 RCU flavors (normal, sched, bh). This
commit therefore updates the full API in the whatisRCU document, thus
encouraging people to use the consolidated RCU update API instead of
the old RCU-bh and RCU-sched update APIs.

Also rcu_dereference is documented to be the same for all 3 mechanisms
(even before the consolidation), however its actually different - as
using the right rcu_dereference primitive (such as rcu_dereference_bh
for bh) is needed to make lock debugging work correctly. This update
also corrects that.

Also, add local_bh_disable() and local_bh_enable() as softirq
protection primitives and correct a grammar error in a quiz answer.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:56:25 -08:00
Joel Fernandes (Google) 70f0508cab doc: rcu: Update description of gp_seq fields in rcu_data
The rcu_state structure doesn't have a gp_seq_needed field. Update the
description under rcu_data accordingly, to reflect this.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: <kernel-team@android.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:56:25 -08:00
Joel Fernandes (Google) 82eccec851 doc: rcu: Better clarify the rcu_segcblist ->len field
An important note under the rcu_segcblist description could use a more
detailed description. Especially explanation of the scenario where the
->head field may be temporarily NULL making it not wise to rely on it
to determine if callbacks are associated with the rcu_segcblist.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: <kernel-team@android.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:56:25 -08:00
Joel Fernandes (Google) b54d9db260 doc: rcu: Update Data-Structures for RCU flavor consolidation
This patch updates all Data-Structures document figures and text and
removes some unwanted figures, to reflect the recent work Paul has been
doing with consolidating all flavors of RCU.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: <kernel-team@android.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:56:25 -08:00
Joel Fernandes (Google) c9b6f899e1 doc: Remove rcu_dynticks from Data-Structures
rcu_dynticks was folded into rcu_data structure. Update the data
structures RCU document accordingly.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: <kernel-team@android.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:49:05 -08:00
Joel Fernandes (Google) 5cc379a42a doc: Update information about resched_cpu
Since commit fced9c8cfe ("rcu: Avoid resched_cpu() when rescheduling
the current CPU"), resched_cpu is not directly called from
sync_sched_exp_handler. Update the documentation about the same.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: <kernel-team@android.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-12 08:48:31 -08:00
Joel Fernandes (Google) dd944caa81 doc: Remove rcu_preempt_state reference in stallwarn
Consolidation of RCU-bh, RCU-preempt, and RCU-sched into one RCU flavor
to rule them all resulted in the removal of rcu_preempt_state.  However,
stallwarn.txt still mentions rcu_preempt_state.  This commit therefore
Updates stallwarn documentation accordingly.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: <kernel-team@android.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-08 21:44:41 -08:00
Joel Fernandes (Google) 2d0350a8f0 doc: Clarify RCU data-structure comment about rcu_tree fanout
RCU Data-Structures document describes a trick to test RCU with small
number of CPUs but with a taller tree. It wasn't immediately clear how
the document arrived at 16 CPUs which also requires setting the
FANOUT_LEAF to 2 instead of the default of 16.  This commit therefore
provides the needed clarification.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: <kernel-team@android.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
2018-11-08 21:44:41 -08:00
Paul E. McKenney 832aa35a65 doc: Set down forward-progress requirements
This commit adds a section to the requirements documentation setting down
requirements for grace-period and callback-invocation forward progress.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-11-08 21:44:41 -08:00
Linus Torvalds 01aa9d518e This is a fairly typical cycle for documentation. There's some welcome
readability improvements for the formatted output, some LICENSES updates
 including the addition of the ISC license, the removal of the unloved and
 unmaintained 00-INDEX files, the deprecated APIs document from Kees, more
 MM docs from Mike Rapoport, and the usual pile of typo fixes and
 corrections.
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Merge tag 'docs-4.20' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "This is a fairly typical cycle for documentation. There's some welcome
  readability improvements for the formatted output, some LICENSES
  updates including the addition of the ISC license, the removal of the
  unloved and unmaintained 00-INDEX files, the deprecated APIs document
  from Kees, more MM docs from Mike Rapoport, and the usual pile of typo
  fixes and corrections"

* tag 'docs-4.20' of git://git.lwn.net/linux: (41 commits)
  docs: Fix typos in histogram.rst
  docs: Introduce deprecated APIs list
  kernel-doc: fix declaration type determination
  doc: fix a typo in adding-syscalls.rst
  docs/admin-guide: memory-hotplug: remove table of contents
  doc: printk-formats: Remove bogus kobject references for device nodes
  Documentation: preempt-locking: Use better example
  dm flakey: Document "error_writes" feature
  docs/completion.txt: Fix a couple of punctuation nits
  LICENSES: Add ISC license text
  LICENSES: Add note to CDDL-1.0 license that it should not be used
  docs/core-api: memory-hotplug: add some details about locking internals
  docs/core-api: rename memory-hotplug-notifier to memory-hotplug
  docs: improve readability for people with poorer eyesight
  yama: clarify ptrace_scope=2 in Yama documentation
  docs/vm: split memory hotplug notifier description to Documentation/core-api
  docs: move memory hotplug description into admin-guide/mm
  doc: Fix acronym "FEKEK" in ecryptfs
  docs: fix some broken documentation references
  iommu: Fix passthrough option documentation
  ...
2018-10-24 18:01:11 +01:00
Henrik Austad a7ddcea58a Drop all 00-INDEX files from Documentation/
This is a respin with a wider audience (all that get_maintainer returned)
and I know this spams a *lot* of people. Not sure what would be the correct
way, so my apologies for ruining your inbox.

The 00-INDEX files are supposed to give a summary of all files present
in a directory, but these files are horribly out of date and their
usefulness is brought into question. Often a simple "ls" would reveal
the same information as the filenames are generally quite descriptive as
a short introduction to what the file covers (it should not surprise
anyone what Documentation/sched/sched-design-CFS.txt covers)

A few years back it was mentioned that these files were no longer really
needed, and they have since then grown further out of date, so perhaps
it is time to just throw them out.

A short status yields the following _outdated_ 00-INDEX files, first
counter is files listed in 00-INDEX but missing in the directory, last
is files present but not listed in 00-INDEX.

List of outdated 00-INDEX:
Documentation: (4/10)
Documentation/sysctl: (0/1)
Documentation/timers: (1/0)
Documentation/blockdev: (3/1)
Documentation/w1/slaves: (0/1)
Documentation/locking: (0/1)
Documentation/devicetree: (0/5)
Documentation/power: (1/1)
Documentation/powerpc: (0/5)
Documentation/arm: (1/0)
Documentation/x86: (0/9)
Documentation/x86/x86_64: (1/1)
Documentation/scsi: (4/4)
Documentation/filesystems: (2/9)
Documentation/filesystems/nfs: (0/2)
Documentation/cgroup-v1: (0/2)
Documentation/kbuild: (0/4)
Documentation/spi: (1/0)
Documentation/virtual/kvm: (1/0)
Documentation/scheduler: (0/2)
Documentation/fb: (0/1)
Documentation/block: (0/1)
Documentation/networking: (6/37)
Documentation/vm: (1/3)

Then there are 364 subdirectories in Documentation/ with several files that
are missing 00-INDEX alltogether (and another 120 with a single file and no
00-INDEX).

I don't really have an opinion to whether or not we /should/ have 00-INDEX,
but the above 00-INDEX should either be removed or be kept up to date. If
we should keep the files, I can try to keep them updated, but I rather not
if we just want to delete them anyway.

As a starting point, remove all index-files and references to 00-INDEX and
see where the discussion is going.

Signed-off-by: Henrik Austad <henrik@austad.us>
Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Just-do-it-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Paul Moore <paul@paul-moore.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Mark Brown <broonie@kernel.org>
Acked-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: [Almost everybody else]
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2018-09-09 15:08:58 -06:00
Paul E. McKenney b56ada1209 Merge branches 'doc.2018.08.30a', 'dynticks.2018.08.30b', 'srcu.2018.08.30b' and 'torture.2018.08.29a' into HEAD
doc.2018.08.30a: Documentation updates
dynticks.2018.08.30b: RCU flavor consolidation updates and cleanups
srcu.2018.08.30b: SRCU updates
torture.2018.08.29a: Torture-test updates
2018-08-30 16:12:53 -07:00
Paul E. McKenney 3e31009898 rcu: Defer reporting RCU-preempt quiescent states when disabled
This commit defers reporting of RCU-preempt quiescent states at
rcu_read_unlock_special() time when any of interrupts, softirq, or
preemption are disabled.  These deferred quiescent states are reported
at a later RCU_SOFTIRQ, context switch, idle entry, or CPU-hotplug
offline operation.  Of course, if another RCU read-side critical
section has started in the meantime, the reporting of the quiescent
state will be further deferred.

This also means that disabling preemption, interrupts, and/or
softirqs will act as an RCU-preempt read-side critical section.
This is enforced by checking preempt_count() as needed.

Some special cases must be handled on an ad-hoc basis, for example,
context switch is a quiescent state even though both the scheduler and
do_exit() disable preemption.  In these cases, additional calls to
rcu_preempt_deferred_qs() override the preemption disabling.  Similar
logic overrides disabled interrupts in rcu_preempt_check_callbacks()
because in this case the quiescent state happened just before the
corresponding scheduling-clock interrupt.

In theory, this change lifts a long-standing restriction that required
that if interrupts were disabled across a call to rcu_read_unlock()
that the matching rcu_read_lock() also be contained within that
interrupts-disabled region of code.  Because the reporting of the
corresponding RCU-preempt quiescent state is now deferred until
after interrupts have been enabled, it is no longer possible for this
situation to result in deadlocks involving the scheduler's runqueue and
priority-inheritance locks.  This may allow some code simplification that
might reduce interrupt latency a bit.  Unfortunately, in practice this
would also defer deboosting a low-priority task that had been subjected
to RCU priority boosting, so real-time-response considerations might
well force this restriction to remain in place.

Because RCU-preempt grace periods are now blocked not only by RCU
read-side critical sections, but also by disabling of interrupts,
preemption, and softirqs, it will be possible to eliminate RCU-bh and
RCU-sched in favor of RCU-preempt in CONFIG_PREEMPT=y kernels.  This may
require some additional plumbing to provide the network denial-of-service
guarantees that have been traditionally provided by RCU-bh.  Once these
are in place, CONFIG_PREEMPT=n kernels will be able to fold RCU-bh
into RCU-sched.  This would mean that all kernels would have but
one flavor of RCU, which would open the door to significant code
cleanup.

Moving to a single flavor of RCU would also have the beneficial effect
of reducing the NOCB kthreads by at least a factor of two.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Apply rcu_read_unlock_special() preempt_count() feedback
  from Joel Fernandes. ]
[ paulmck: Adjust rcu_eqs_enter() call to rcu_preempt_deferred_qs() in
  response to bug reports from kbuild test robot. ]
[ paulmck: Fix bug located by kbuild test robot involving recursion
  via rcu_preempt_deferred_qs(). ]
2018-08-30 16:02:34 -07:00
Paul E. McKenney 5c3f78ec28 doc: Fix broken HTML directive
This commit adds the needed "<".

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 11:01:08 -07:00
Paul E. McKenney 77095901b8 doc: Update removal of RCU-bh/sched update machinery
The RCU-bh update API is now defined in terms of that of RCU-bh and
RCU-sched, so this commit updates the documentation accordingly.

In addition, although RCU-sched persists in !PREEMPT kernels, in
the PREEMPT case its update API is now defined in terms of that of
RCU-preempt, so this commit also updates the documentation accordingly.

While in the area, this commit removes the documentation for the
now-obsolete synchronize_rcu_mult() and clarifies the Tasks RCU
documentation.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-30 10:59:48 -07:00
Joel Fernandes (Google) ea24c125fe doc: Improve rcu_dynticks::dynticks documentation
The very useful RCU Data-Structures describes that the dynticks counter
of the rcu_dynticks data structure is incremented when we transitions to
or from dynticks-idle mode. However it doesn't mention that it is also
incremented due to transitions to and from user mode which for dynticks
purposes is an extended quiescent state.

I found this with tracing calls to rcu_dynticks_eqs_enter which can also
happen from rcu_user_enter. Lets add this information to the
Data-Structures document.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-29 08:54:30 -07:00
Joel Fernandes (Google) a5a2889544 doc: Fix broken RCU-requirements link to LKML archive
Two of the Requirements.html LKML links are broken. This patch changes
them to use the archive from lore.kernel.org, which works fine.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-29 08:54:30 -07:00
Paul E. McKenney e77cb32558 doc: Add design documentation on interruption of NMI handlers
Make Requirements.html talk about how NMI handlers can take what appear
to RCU to be normal interrupts.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-08-29 08:54:14 -07:00
NeilBrown b7b6f94cf6 rculist: Improve documentation for list_for_each_entry_from_rcu()
Unfortunately the patch for adding list_for_each_entry_from_rcu()
wasn't the final patch after all review.  It is functionally
correct but the documentation was incomplete.

This patch adds this missing documentation which includes an update to
the documentation for list_for_each_entry_continue_rcu() to match the
documentation for the new list_for_each_entry_from_rcu(), and adds
list_for_each_entry_from_rcu() and the already existing
hlist_for_each_entry_from_rcu() to section 7 of whatisRCU.txt.

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-07-12 15:39:25 -07:00
Andrea Parri 264d4f88ad doc: Update synchronize_rcu() definition in whatisRCU.txt
The synchronize_rcu() definition based on RW-locks in whatisRCU.txt
does not meet the "Memory-Barrier Guarantees" in Requirements.html;
for example, the following SB-like test:

    P0:                      P1:

    WRITE_ONCE(x, 1);        WRITE_ONCE(y, 1);
    synchronize_rcu();       smp_mb();
    r0 = READ_ONCE(y);       r1 = READ_ONCE(x);

should not be allowed to reach the state "r0 = 0 AND r1 = 0", but
the current write_lock()+write_unlock() definition can not ensure
this.  This commit therefore inserts an smp_mb__after_spinlock()
in order to cause this synchronize_rcu() implementation to provide
this memory-barrier guarantee.

Suggested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-07-12 15:39:23 -07:00
Paul E. McKenney e1333462e3 doc: Update RCU CPU stall-warning documentation
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-07-12 15:38:51 -07:00
Paul E. McKenney 869cc745bf doc: Update memory-ordering documentation for ->gp-seq
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-07-12 15:38:51 -07:00
Paul E. McKenney b1e1f21f5b doc: Update data-structure documentation for ->gp_seq
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2018-07-12 15:38:49 -07:00
Paul Gortmaker 628c08420b doc: Ensure whatisRCU.txt actually says what RCU is
It came to my attention that the file "whatisRCU.txt" does not
manage to actually ever spell out what is RCU.

This might not be an issue for a lot of people, but we have to
assume the consumers of these documents are starting from ground
zero; otherwise they'd not be reading the docs.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tested-by: Nicholas Piggin <npiggin@gmail.com>
2018-05-15 10:28:12 -07:00
Paul E. McKenney 1dfa55e019 Merge branches 'cond_resched.2017.12.04a', 'dyntick.2017.11.28a', 'fixes.2017.12.11a', 'srbd.2017.12.05a' and 'torture.2017.12.11a' into HEAD
cond_resched.2017.12.04a: Convert cond_resched_rcu_qs() to cond_resched()
dyntick.2017.11.28a: Make RCU dynticks handle interrupts from NMI
fixes.2017.12.11a: Miscellaneous fixes
srbd.2017.12.05a: Remove now-redundant smp_read_barrier_depends()
torture.2017.12.11a: Torture-testing update
2017-12-11 09:21:58 -08:00
Paul E. McKenney 9ad3c143d7 doc: De-emphasize smp_read_barrier_depends
This commit keeps only the historical and low-level discussion of
smp_read_barrier_depends().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Adjusted to allow for David Howells feedback on prior commit. ]
2017-12-05 11:57:53 -08:00
Paul E. McKenney f2b1760aed doc: Eliminate cond_resched_rcu_qs() in favor of cond_resched()
Now that cond_resched() also provides RCU quiescent states when
needed, it can be used in place of cond_resched_rcu_qs().  This
commit therefore documents this change.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-12-04 10:28:59 -08:00
Paul E. McKenney 3af3999b9a doc: Update dyntick-idle design documentation for NMI/irq consolidation
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-11-28 15:51:22 -08:00
Linus Torvalds 6098850e7e Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull RCU updates from Ingo Molnar:
 "The main changes in this cycle are:

   - Documentation updates

   - RCU CPU stall-warning updates

   - Torture-test updates

   - Miscellaneous fixes

  Size wise the biggest updates are to documentation. Excluding
  documentation most of the code increase comes from a single commit
  which expands debugging"

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (24 commits)
  srcu: Add parameters to SRCU docbook comments
  doc: Rewrite confusing statement about memory barriers
  memory-barriers.txt: Fix typo in pairing example
  rcu/segcblist: Include rcupdate.h
  rcu: Add extended-quiescent-state testing advice
  rcu: Suppress lockdep false-positive ->boost_mtx complaints
  rcu: Do not include rtmutex_common.h unconditionally
  torture: Provide TMPDIR environment variable to specify tmpdir
  rcutorture: Dump writer stack if stalled
  rcutorture: Add interrupt-disable capability to stall-warning tests
  rcu: Suppress RCU CPU stall warnings while dumping trace
  rcu: Turn off tracing before dumping trace
  rcu: Make RCU CPU stall warnings check for irq-disabled CPUs
  sched,rcu: Make cond_resched() provide RCU quiescent state
  sched: Make resched_cpu() unconditional
  irq_work: Map irq_work_on_queue() to irq_work_on() in !SMP
  rcu: Create call_rcu_tasks() kthread at boot time
  rcu: Fix up pending cbs check in rcu_prepare_for_idle
  memory-barriers: Rework multicopy-atomicity section
  memory-barriers: Replace uses of "transitive"
  ...
2017-11-13 12:18:10 -08:00
Tom Saeger d354a6f150 Documentation: fix ref to workqueue content
Signed-off-by: Tom Saeger <tom.saeger@oracle.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2017-10-19 12:57:26 -06:00
Paul E. McKenney d3cf5176d0 documentation: Update RCU CPU stall warning messages
The RCU CPU stall warnings have morphed significantly since the last
update, so this commit brings the documentation up to date.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-10-09 14:23:36 -07:00
Paul E. McKenney 3d916a443e documentation: Slow systems can stall RCU grace periods
If a fast system has a worst-case grace-period duration of (say) ten
seconds, then running the same workload on a system ten times as slow
will get you an RCU CPU stall warning given default stall-warning
timeout settings.  This commit therefore adds this possibility to
stallwarn.txt.

Reported-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-10-09 14:23:36 -07:00
Paul E. McKenney dfa0ee48ef documentation: Long-running irq handlers can stall RCU grace periods
If a periodic interrupt's handler takes longer to execute than the period
between successive interrupts, RCU's kthreads and softirq handlers can
be prevented from executing, resulting in otherwise inexplicable RCU
CPU stall warnings.  This commit therefore calls out this possibility
in Documentation/RCU/stallwarn.txt.

Reported-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-10-09 14:23:36 -07:00
Paul E. McKenney bb7e5ce7dd documentation: RCU grace-period memory ordering guarantees
This commit provides text and diagrams showing how Tree RCU implements
its grace-period memory ordering guarantees.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
2017-10-09 14:23:36 -07:00
Paul E. McKenney 850bf6d592 doc: Set down RCU's scheduling-clock-interrupt needs
This commit documents the situations in which RCU needs the
scheduling-clock interrupt to be enabled, along with the consequences
of failing to meet RCU's needs in this area.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-08-17 07:31:14 -07:00
Paul E. McKenney 8a597d636f doc: No longer allowed to use rcu_dereference on non-pointers
There are too many ways for the compiler to optimize (that is, break)
dependencies carried via integer values, so it is now permissible to
carry dependencies only via pointers.  This commit catches up some of
the documentation on this point.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-08-17 07:29:58 -07:00
Paul E. McKenney 4de5f89ef8 doc: Update RCU documentation
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-08-17 07:29:48 -07:00
Paul E. McKenney ae91aa0adb rcu: Remove debugfs tracing
RCU's debugfs tracing used to be the only reasonable low-level debug
information available, but ftrace and event tracing has since surpassed
the RCU debugfs level of usefulness.  This commit therefore removes
RCU's debugfs tracing.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-06-08 18:52:43 -07:00
Paul E. McKenney 41a2901e7d rcu: Remove SPARSE_RCU_POINTER Kconfig option
The sparse-based checking for non-RCU accesses to RCU-protected pointers
has been around for a very long time, and it is now the only type of
sparse-based checking that is optional.  This commit therefore makes
it unconditional.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
2017-06-08 18:52:41 -07:00
Paul E. McKenney fe5ac724d8 rcu: Remove nohz_full full-system-idle state machine
The NO_HZ_FULL_SYSIDLE full-system-idle capability was added in 2013
by commit 0edd1b1784 ("nohz_full: Add full-system-idle state machine"),
but has not been used.  This commit therefore removes it.

If it turns out to be needed later, this commit can always be reverted.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-06-08 18:52:39 -07:00
Paul E. McKenney c75e9caaf8 doc: Take tail recursion into account in RCU requirements
This commit classifies tail recursion as an alternative way to write
a loop, with similar limitations.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-06-08 08:25:34 -07:00
Paul E. McKenney 09f501a0f0 srcu: Document auto-expediting requirement
This commit documents the auto-expediting requirement satisfied by
commits 2da4b2a7fd ("srcu: Expedite first synchronize_srcu() when idle")
and 22607d66bb ("srcu: Specify auto-expedite holdoff time").

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-06-08 08:25:33 -07:00
Paul E. McKenney f2094107ac Merge branches 'doc.2017.04.12a', 'fixes.2017.04.19a' and 'srcu.2017.04.21a' into HEAD
doc.2017.04.12a: Documentation updates
fixes.2017.04.19a: Miscellaneous fixes
srcu.2017.04.21a: Parallelize SRCU callback handling
2017-04-21 06:00:13 -07:00
Paul E. McKenney 5f0d5a3ae7 mm: Rename SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU
A group of Linux kernel hackers reported chasing a bug that resulted
from their assumption that SLAB_DESTROY_BY_RCU provided an existence
guarantee, that is, that no block from such a slab would be reallocated
during an RCU read-side critical section.  Of course, that is not the
case.  Instead, SLAB_DESTROY_BY_RCU only prevents freeing of an entire
slab of blocks.

However, there is a phrase for this, namely "type safety".  This commit
therefore renames SLAB_DESTROY_BY_RCU to SLAB_TYPESAFE_BY_RCU in order
to avoid future instances of this sort of confusion.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-mm@kvack.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
[ paulmck: Add comments mentioning the old name, as requested by Eric
  Dumazet, in order to help people familiar with the old name find
  the new one. ]
Acked-by: David Rientjes <rientjes@google.com>
2017-04-18 11:42:36 -07:00
Paul E. McKenney 9226b10d78 rcu: Place guard on rcu_all_qs() and rcu_note_context_switch() actions
The rcu_all_qs() and rcu_note_context_switch() do a series of checks,
taking various actions to supply RCU with quiescent states, depending
on the outcomes of the various checks.  This is a bit much for scheduling
fastpaths, so this commit creates a separate ->rcu_urgent_qs field in
the rcu_dynticks structure that acts as a global guard for these checks.
Thus, in the common case, rcu_all_qs() and rcu_note_context_switch()
check the ->rcu_urgent_qs field, find it false, and simply return.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
2017-04-18 11:38:18 -07:00
Paul E. McKenney 0f9be8cabb rcu: Eliminate flavor scan in rcu_momentary_dyntick_idle()
The rcu_momentary_dyntick_idle() function scans the RCU flavors, checking
that one of them still needs a quiescent state before doing an expensive
atomic operation on the ->dynticks counter.  However, this check reduces
overhead only after a rare race condition, and increases complexity.  This
commit therefore removes the scan and the mechanism enabling the scan.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-04-18 11:38:18 -07:00
Paul E. McKenney 9577df9a31 rcu: Pull rcu_qs_ctr into rcu_dynticks structure
The rcu_qs_ctr variable is yet another isolated per-CPU variable,
so this commit pulls it into the pre-existing rcu_dynticks per-CPU
structure.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-04-18 11:38:17 -07:00
Paul E. McKenney abb06b9948 rcu: Pull rcu_sched_qs_mask into rcu_dynticks structure
The rcu_sched_qs_mask variable is yet another isolated per-CPU variable,
so this commit pulls it into the pre-existing rcu_dynticks per-CPU
structure.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-04-18 11:38:17 -07:00
Paul E. McKenney d3d3a3ccc4 doc: Emphasize that "toy" RCU requires recursive rwlock
Reported-by: "yangzc@uit.com.cn" <yangzc@uit.com.cn>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-04-12 08:23:43 -07:00
Michalis Kokologiannakis 93728af0a1 doc: Update the comparisons rule in rcu_dereference.txt
When an RCU-protected pointer is fetched but never dereferenced
rcu_access_pointer() should be used in place of rcu_dereference().
This commit explicitly records this very fact in Documentation/
RCU/rcu_dereference.txt, in order to prevent the usage of
rcu_dereference() in comparisons.

Signed-off-by: Michalis Kokologiannakis <mixaskok@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-04-12 08:23:42 -07:00
Paul E. McKenney 066bb1c84a doc: Update rcu_assign_pointer() definition in whatisRCU.txt
The rcu_assign_pointer() macro has changed over time, and the version
in Documentation/RCU/whatisRCU.txt has not kept up.  This commit brings
it into 2017, albeit in a simplified fashion.

Reported-by: Andrea Parri <parri.andrea@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-04-12 08:23:42 -07:00
Paul E. McKenney 6771853bce doc: Update requirements based on recent changes
These changes include lighter-weight expedited grace periods, the fact
that expedited grace periods and rcu_barrier() no longer block CPU
hotplug, some HTML font fixups, noting that rcu_barrier() need not wait
for a grace period (even if callbacks are posted), the fact that SRCU
read-side critical sections can be used from offline CPUs, and the fact
that SRCU now maintains per-CPU callback lists.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-04-12 08:23:41 -07:00
Paul E. McKenney aa123a748e doc: Update RCU data-structure documentation for rcu_segcblist
The rcu_segcblist data structure, which contains segmented lists
of RCU callbacks, was recently added.  This commit updates the
documentation accordingly.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-04-12 08:23:41 -07:00
Paul E. McKenney 8e2a439753 doc: Update stallwarn.txt to make causes more prominent
This commit rearranges the Documentation/RCU/stallwarn.txt file to
put the list of issues that can cause RCU CPU stall warnings near
the beginning of the document.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-04-12 08:23:40 -07:00
Paul E. McKenney b4553f0cfe doc: Add mid-boot operation to expedited grace periods
This commit adds a description of how expedited grace periods operate
during the mid-boot "dead zone", which starts when the scheduler spawns
the first kthread and ends when all of RCU's kthreads have been spawned.
In short, before mid-boot, synchronous grace periods can be a no-op.
After the end of mid-boot, workqueues may be used.  During mid-boot,
the requesting task drivees the expedited grace period.

For more detail, see https://lwn.net/Articles/716148/.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-04-12 08:23:40 -07:00
Paul E. McKenney f1387d7705 doc: Synchronous RCU grace periods are now legal throughout boot
This commit updates the "Early Boot" section of the RCU requirements
to describe how synchronous RCU grace periods are now legal throughout
the boot process.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2017-04-12 08:23:39 -07:00
Paul E. McKenney 31945aa9f1 Merge branches 'doc.2017.01.15b', 'dyntick.2017.01.23a', 'fixes.2017.01.23a', 'srcu.2017.01.25a' and 'torture.2017.01.15b' into HEAD
doc.2017.01.15b: Documentation updates
dyntick.2017.01.23a: Dyntick tracking consolidation
fixes.2017.01.23a: Miscellaneous fixes
srcu.2017.01.25a: SRCU rewrite, fixes, and verification
torture.2017.01.15b: Torture-test updates
2017-01-25 12:56:05 -08:00
Paul E. McKenney bb4e2c08bb rcu: Eliminate unused expedited_normal counter
Expedited grace periods no longer fall back to normal grace periods
in response to lock contention, given that expedited grace periods
now use the rcu_node tree so as to avoid contention.  This commit
therfore removes the expedited_normal counter.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2017-01-23 11:37:14 -08:00
Paul E. McKenney 4afac159c3 doc: Quick-Quiz answers are now inline
Now that quick-quiz answers are inline, there is no separate section
containing those answers.  This commit therefore removes the dangling
reference from the RCU data-structures design documentation.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2017-01-14 21:30:33 -08:00
Tetsuo Handa 526914a0ae doc: Fix RCU requirements typos
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2017-01-14 21:29:10 -08:00
Paul E. McKenney e73c14ebc3 rcu: Design documentation for expedited grace periods
This commit adds design documentation for expedited grace periods.
This documentation is in HTML rather than the new documentation
format because (1) I have prototype documentation already in HTML,
and (2) Attempting to learn the new documentation format while
creating the design documentation seems likely to result in neither
happening in a timely fashion.

Once the design documentation is complete, we can start a conversion effort.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2017-01-14 21:28:58 -08:00
Pranith Kumar 8cf503d337 Documentation/RCU: Fix minor typo
deference should actually be dereference.

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-11-14 10:39:48 -08:00
Paul E. McKenney e2c85cb12c documentation: Present updated RCU guarantee
Recent memory-model work deduces the relationships of RCU read-side
critical sections and grace periods based on the relationships of
accesses within a critical section and accesses preceding and following
the grace period.  This commit therefore adds this viewpoint.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-11-14 10:39:36 -08:00
Petr Mladek 3989144f86 kthread: kthread worker API cleanup
A good practice is to prefix the names of functions by the name
of the subsystem.

The kthread worker API is a mix of classic kthreads and workqueues.  Each
worker has a dedicated kthread.  It runs a generic function that process
queued works.  It is implemented as part of the kthread subsystem.

This patch renames the existing kthread worker API to use
the corresponding name from the workqueues API prefixed by
kthread_:

__init_kthread_worker()		-> __kthread_init_worker()
init_kthread_worker()		-> kthread_init_worker()
init_kthread_work()		-> kthread_init_work()
insert_kthread_work()		-> kthread_insert_work()
queue_kthread_work()		-> kthread_queue_work()
flush_kthread_work()		-> kthread_flush_work()
flush_kthread_worker()		-> kthread_flush_worker()

Note that the names of DEFINE_KTHREAD_WORK*() macros stay
as they are. It is common that the "DEFINE_" prefix has
precedence over the subsystem names.

Note that INIT() macros and init() functions use different
naming scheme. There is no good solution. There are several
reasons for this solution:

  + "init" in the function names stands for the verb "initialize"
    aka "initialize worker". While "INIT" in the macro names
    stands for the noun "INITIALIZER" aka "worker initializer".

  + INIT() macros are used only in DEFINE() macros

  + init() functions are used close to the other kthread()
    functions. It looks much better if all the functions
    use the same scheme.

  + There will be also kthread_destroy_worker() that will
    be used close to kthread_cancel_work(). It is related
    to the init() function. Again it looks better if all
    functions use the same naming scheme.

  + there are several precedents for such init() function
    names, e.g. amd_iommu_init_device(), free_area_init_node(),
    jump_label_init_type(),  regmap_init_mmio_clk(),

  + It is not an argument but it was inconsistent even before.

[arnd@arndb.de: fix linux-next merge conflict]
 Link: http://lkml.kernel.org/r/20160908135724.1311726-1-arnd@arndb.de
Link: http://lkml.kernel.org/r/1470754545-17632-3-git-send-email-pmladek@suse.com
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@suse.de>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-10-11 15:06:33 -07:00
Paul E. McKenney ed2bec07fd documentation: Record reason for rcu_head two-byte alignment
There is an assertion in __call_rcu() that checks only the bottom
bit of the rcu_head pointer, rather than the bottom two (as might be
expected for 32-bit systems) or the bottom three (as might be expected
for 64-bit systems).  This choice might be a bit surprising in these days
of ubiquitous 32-bit and 64-bit systems.  This commit therefore records
the reason for this odd alignment check, namely that m68k guarantees
only two-byte alignment despite being a 32-bit architectures.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-08-22 09:25:33 -07:00
SeongJae Park e1ef69217f rcutorture: Remove outdated config option description
CONFIG_RCU_TORTURE_TEST_RUNNABLE was removed by commit 4e9a073f60
("torture: Remove CONFIG_RCU_TORTURE_TEST_RUNNABLE, simplify code"),
but the documentation was not updated accordingly.  This commit therefore
updates the documentation to reflect CONFIG_RCU_TORTURE_TEST_RUNNABLE's
removal and to add a description for the alternative module parameter.

Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-08-22 09:23:23 -07:00
Eric Engestrom 14ef05754f Documentation: Fix spelling mistake
Signed-off-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-06-14 16:01:00 -07:00
Paul E. McKenney c79dac758d documentation: Add RCU_NONIDLE() restrictions to requirements
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-06-14 16:00:59 -07:00
Paul E. McKenney db4855b5a8 documentation: Add references to 2010 and 2014 Big API Tables
Reported-by: Jim Roskind <jar@roskind.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-06-14 16:00:58 -07:00
Paul E. McKenney 2921b12362 documentation: Add reference to 2014 RCU API LWN article
Reported-by: Jim Roskind <jar@roskind.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-06-14 16:00:58 -07:00
Linus Torvalds e9ad9b9bd3 The most interesting thing (IMO) this time around is some beginning
infrastructural work to allow documents to be written using restructured
 text.  Maybe someday, in a galaxy far far away, we'll be able to eliminate
 the DocBook dependency and have a much better integrated set of kernel
 docs.  Someday.
 
 Beyond that, there's a new document on security hardening from Kees, the
 movement of some sample code over to samples/, a number of improvements to
 the serial docs from Geert, and the usual collection of corrections, typo
 fixes, etc.
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Merge tag 'docs-for-linus' of git://git.lwn.net/linux

Pull Documentation updates from Jon Corbet:
 "A bit busier this time around.

  The most interesting thing (IMO) this time around is some beginning
  infrastructural work to allow documents to be written using
  restructured text.  Maybe someday, in a galaxy far far away, we'll be
  able to eliminate the DocBook dependency and have a much better
  integrated set of kernel docs.  Someday.

  Beyond that, there's a new document on security hardening from Kees,
  the movement of some sample code over to samples/, a number of
  improvements to the serial docs from Geert, and the usual collection
  of corrections, typo fixes, etc"

* tag 'docs-for-linus' of git://git.lwn.net/linux: (55 commits)
  doc: self-protection: provide initial details
  serial: doc: Use port->state instead of info
  serial: doc: Always refer to tty_port->mutex
  Documentation: vm: Spelling s/paltform/platform/g
  Documentation/memcg: update kmem limit doc as codes behavior
  docproc: print a comment about autogeneration for rst output
  docproc: add support for reStructuredText format via --rst option
  docproc: abstract terminating lines at first space
  docproc: abstract docproc directive detection
  docproc: reduce unnecessary indentation
  docproc: add variables for subcommand and filename
  kernel-doc: use rst C domain directives and references for types
  kernel-doc: produce RestructuredText output
  kernel-doc: rewrite usage description, remove duplicated comments
  Doc: correct the location of sysrq.c
  Documentation: fix common spelling mistakes
  samples: v4l: from Documentation to samples directory
  samples: connector: from Documentation to samples directory
  Documentation: xillybus: fix spelling mistake
  Documentation: x86: fix spelling mistakes
  ...
2016-05-19 18:07:25 -07:00
Kees Cook 08559657b2 Documentation: fix common spelling mistakes
This fixes several spelling mistakes in the Documentation/ tree, which
are caught by checkpatch.pl's spell checking.

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2016-04-28 07:51:59 -06:00
Paul E. McKenney dcd36d01fb Merge branches 'doc.2016.04.19a', 'exp.2016.03.31d', 'fixes.2016.03.31d' and 'torture.2016.04.21a' into HEAD
doc.2016.04.19a: Documentation updates
exp.2016.03.31d: Expedited grace-period updates
fixes.2016.03.31d: Miscellaneous fixes
torture.2016.004.21a Torture-test updates
2016-04-21 13:48:20 -07:00
Paul E. McKenney 5c1458478c documentation: Add documentation for RCU's major data structures
This commit adds documentation for RCU's major data structures,
including rcu_state, rcu_node, rcu_data, rcu_dynticks, and rcu_head.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-04-19 14:48:12 -07:00
Paul E. McKenney e2fd9d3584 rcu: Remove expedited GP funnel-lock bypass
Commit #cdacbe1f91264 ("rcu: Add fastpath bypassing funnel locking")
turns out to be a pessimization at high load because it forces a tree
full of tasks to wait for an expedited grace period that they probably
do not need.  This commit therefore removes this optimization.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31 13:34:07 -07:00
Paul E. McKenney 0c7d10e4b9 documentation: Emphasize the call_rcu() is illegal from idle
Although call_rcu()'s fastpath works just fine on an idle CPU,
some branches of the slowpath invoke the scheduler, which uses
RCU.  Therefore, this commit emphasizes the fact that call_rcu()
must not be invoked from an idle CPU.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31 13:33:23 -07:00
Paul E. McKenney 5413e24c94 documentation: Sharpen up the no-readers quick quiz
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31 13:33:23 -07:00
Paul E. McKenney 6146f8df48 documentation: Get rid of duplicate .htmlx file
This commit uses colors to obscure the quick-quiz answers, thus getting
rid of the .htmlx file.  Use your mouse to select the answer in order
to see the text.  Alternatively, use your favorite scripting language
to remove all occurences of "<font color="ffffff">" from the file.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31 13:33:22 -07:00
Paul E. McKenney 11a65df573 documentation: Remove unnecessary images from requirements
This commit removes a cutesy cartoon and also a diagram that can
just as easily be represented by text.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31 13:33:21 -07:00
Paul E. McKenney 514f1eb5f4 documentation: Document illegality of call_rcu() from offline CPUs
There is already a blanket statement about no member of RCU's API
being legal from an offline CPU, but add an explicit note where it
states that it is illegal to invoke call_rcu() from an NMI handler.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31 13:33:21 -07:00
Paul E. McKenney d8936c0b7e documentation: Explain why rcu_read_lock() needs no barrier()
This commit adds a Quick Quiz whose answer explains why the compiler
code reordering enabled by CONFIG_PREEMPT=n's empty rcu_read_lock()
and rcu_read_unlock() functions does not hinder RCU's ability to figure
out which RCU read-side critical sections have completed and not.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31 13:33:20 -07:00
Paul E. McKenney f43b62542e documentation: Add synchronize_rcu_mult() to the requirements
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31 13:33:20 -07:00
Paul E. McKenney 41abcf321d documentation: Add real-time requirements from CPU-bound workloads
This commit records RCU's responsibility to avoid degrading latencies
of CPUs running tight loops within properly configured workloads,
both in kernel and in userspace.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31 13:33:19 -07:00
Yao Dongdong 70946a44de documentation: Make sample code and documentation consistent
In the chapter 'analogy with reader-writer locking', the sample
code uses spinlock_t in reader-writer case. Just correct it so
that we can read the document easily.

Signed-off-by: Yao Dongdong <yaodongdong@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2016-03-31 13:33:19 -07:00
Paul E. McKenney c64c4b0f9a documentation: Update RCU requirements based on expedited changes
Because RCU-sched expedited grace periods now use IPIs and interact
with rcu_read_unlock(), it is no longer sufficient to disable preemption
across RCU read-side critical sections that acquire and hold scheduler
locks.  It is now necessary to instead disable interrupts.  This commit
documents this change.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05 12:34:32 -08:00
Paul E. McKenney 4b689330b1 documentation: Clarify RCU memory barriers and requirements
The RCU requirements do not make it absolutely clear that the
memory-barrier requirements are not intended to replace the fundamental
requirement that all pre-existing RCU readers complete before a grace
period completes.  This commit therefore pulls the memory-barrier
requirements into a separate section and explicitly calls out the
relationship between the memory-barrier requirements and the fundamental
requirement.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05 12:33:37 -08:00
Paul E. McKenney a4b575627e documentation: Expand on scheduler/RCU deadlock requirements
This commit adds a second option for avoiding scheduler/RCU deadlocks,
namely that preemption be disabled across the entire RCU read-side
critical section in question.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05 12:33:26 -08:00
Paul E. McKenney 0825458b1d documentation: Composability analogies
This commit expands on RCU's composability by comparing it to that of
transactional memory and of locking.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05 12:33:11 -08:00
Paul E. McKenney 01d3ad3834 documentation: Cover requirements controlling stall warnings
This commit adds verbiage on boot and sysfs parameters that can be
used to control RCU CPU stall warnings, both to change the timeout
and to suppress these warnings entirely.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-12-05 12:32:19 -08:00
Paul E. McKenney 701e80312f Documentation: Record bottom-bit-zero guarantee for ->next
This commit records RCU's guarantee that the bottom bit of the rcu_head
structure's ->next field will remain zero for callbacks posted via
call_rcu(), but not necessarily for <tt>kfree_rcu()</tt> or some
possible future call_rcu_lazy() variant that might one day be created
for energy-efficiency purposese.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Updates URLs as suggested by Josh Triplett. ]
2015-12-05 12:31:47 -08:00
Paul E. McKenney 649e4368ff documentation: Record RCU requirements
This commit adds RCU requirements as published in a 2015 LWN series.
Bringing these requirements in-tree allows them to be updated as changes
are discovered.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Updates to charset and URLs as suggested by Josh Triplett. ]
2015-12-05 12:19:07 -08:00
Paul E. McKenney 39cd2dd39a Merge branches 'doc.2015.10.06a', 'percpu-rwsem.2015.10.06a' and 'torture.2015.10.06a' into HEAD
doc.2015.10.06a:  Documentation updates.
percpu-rwsem.2015.10.06a:  Optimization of per-CPU reader-writer semaphores.
torture.2015.10.06a:  Torture-test updates.
2015-10-07 16:06:25 -07:00
Paul E. McKenney b672adf8cf documentation: Catch up list of torture_type options
This commit rids the documentation of long-obsolete torture_type options
such as rcu_sync and adds new ones such as tasks.  Also add verbiage
noting the fact that rcutorture now concurrently tests the asynchrounous,
synchronous, expedited synchronous, and polling grace-period primitives.

Reported-by: David Miller <davem@davemloft.net>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: David Miller <davem@davemloft.net>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2015-10-06 11:22:48 -07:00
Jason A. Donenfeld 2c4ac34bc2 documentation: Correct doc to use rcu_dereference_protected
As there is lots of misinformation and outdated information on the
Internet about nearly all topics related to the kernel, I thought it
would be best if I based my RCU code on the guidelines of the examples
in the Documentation/ tree of the latest kernel. One thing that stuck
out when reading the whatisRCU.txt document was, "interesting how we
don't need any function to dereference rcu protected pointers when doing
updates if a lock is held. I wonder how static analyzers will work with
that." Then, a few weeks later, upon discovering sparse's __rcu support,
I ran it over my code, and lo and behold, things weren't done right.
Examining other RCU usages in the kernel reveal consistent usage of
rcu_dereference_protected, passing in lockdep_is_held as the
conditional. So, this patch adds that idiom to the documentation, so
that others ahead of me won't endure the same exercise.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2015-10-06 11:22:43 -07:00
Paul E. McKenney da873def8d documentation: Call out slow consoles as cause of stall warnings
The Linux kernel outputs copious text during boot, and a slow serial
console can result in stall warnings, particularly when messages are
printed with interrupts disabled.  This commit adds this to the list
of causes of RCU CPU stall warning messages.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2015-10-06 11:22:38 -07:00
Paul E. McKenney 0d43eb34f9 rcu: Invert passed_quiesce and rename to cpu_no_qs
This commit inverts the sense of the rcu_data structure's ->passed_quiesce
field and renames it to ->cpu_no_qs.  This will allow a later commit to
use an "aggregate OR" operation to test expedited as well as normal grace
periods without added overhead.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-09-20 21:16:21 -07:00
Paul E. McKenney 3dbe43f6fb Merge branches 'doc.2015.07.15a' and 'torture.2015.07.15a' into HEAD
doc.2015.07.15a: Documentation updates.
torture.2015.07.15a: Torture-test updates.
2015-08-04 08:42:02 -07:00
Paul E. McKenney 8ff4fbfd69 Merge branches 'fixes.2015.07.22a' and 'initexp.2015.08.04a' into HEAD
fixes.2015.07.22a: Miscellaneous fixes.
initexp.2015.08.04a: Initialization and expedited updates.
	(Single branch due to conflicts.)
2015-08-04 08:40:58 -07:00
Paul E. McKenney f78f5b90c4 rcu: Rename rcu_lockdep_assert() to RCU_LOCKDEP_WARN()
This commit renames rcu_lockdep_assert() to RCU_LOCKDEP_WARN() for
consistency with the WARN() series of macros.  This also requires
inverting the sense of the conditional, which this commit also does.

Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
2015-07-22 15:27:32 -07:00
Paul E. McKenney cdacbe1f91 rcu: Add fastpath bypassing funnel locking
In the common case, there will be only one expedited grace period in
the system at a given time, in which case it is not helpful to use
funnel locking.  This commit therefore adds a fastpath that bypasses
funnel locking when the root ->exp_funnel_mutex is not held.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-07-17 14:59:06 -07:00
Paul E. McKenney 99a930b0d2 documentation: Describe new expedited stall warnings
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-07-17 14:59:03 -07:00
Paul E. McKenney 75c27f119b rcu: Remove CONFIG_RCU_CPU_STALL_INFO
The CONFIG_RCU_CPU_STALL_INFO has been default-y for a couple of
releases with no complaints, so it is time to eliminate this Kconfig
option entirely, so that the long-form RCU CPU stall warnings cannot
be disabled.  This commit does just that.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-07-17 14:58:44 -07:00
Paul E. McKenney 297f739938 documentation: Fix spelling of "operators"
Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-07-15 14:43:10 -07:00
Linus Torvalds 1e467e68e5 Documentation updates for 4.2
The main thing here is Ingo's big subdirectory documenting feature support
 for each architecture.  Beyond that, it's the usual pile of fixes, tweaks,
 and small additions.
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Merge tag 'docs-for-linus' of git://git.lwn.net/linux-2.6

Pull documentation updates from Jonathan Corbet:
 "The main thing here is Ingo's big subdirectory documenting feature
  support for each architecture.  Beyond that, it's the usual pile of
  fixes, tweaks, and small additions"

* tag 'docs-for-linus' of git://git.lwn.net/linux-2.6: (79 commits)
  doc:md: fix typo in md.txt.
  Documentation/mic/mpssd: don't build x86 userspace when cross compiling
  Documentation/prctl: don't build tsc tests when cross compiling
  Documentation/vDSO: don't build tests when cross compiling
  Doc:ABI/testing: Fix typo in sysfs-bus-fcoe
  Doc: Docbook: Change wikipedia's URL from http to https in scsi.tmpl
  Doc: Change wikipedia's URL from http to https
  Documentation/kernel-parameters: add missing pciserial to the earlyprintk
  Doc:pps: Fix typo in pps.txt
  kbuild : Fix documentation of INSTALL_HDR_PATH
  Documentation: filesystems: updated struct file_operations documentation in vfs.txt
  kbuild: edit explanation of clean-files variable
  Doc: ja_JP: Fix typo in HOWTO
  Move freefall program from Documentation/ to tools/
  Documentation: ARM: EXYNOS: Describe boot loaders interface
  Doc:nfc: Fix typo in nfc-hci.txt
  vfs: Minor documentation fix
  Doc: networking: txtimestamp: fix printf format warning
  Documentation, intel_pstate: Improve legacy mode internal governors description
  Documentation: extend use case for EXPORT_SYMBOL_GPL()
  ...
2015-06-24 20:01:36 -07:00
Masanari Iida ae13c65bc7 Doc: Change wikipedia's URL from http to https
Recently wikipedia announced to secure access to the servers.
Now all http access re-route to https.

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
2015-06-22 10:14:05 -06:00
Paul E. McKenney 0868aa2216 Merge branches 'array.2015.05.27a', 'doc.2015.05.27a', 'fixes.2015.05.27a', 'hotplug.2015.05.27a', 'init.2015.05.27a', 'tiny.2015.05.27a' and 'torture.2015.05.27a' into HEAD
array.2015.05.27a:  Remove all uses of RCU-protected array indexes.
doc.2015.05.27a:  Docuemntation updates.
fixes.2015.05.27a:  Miscellaneous fixes.
hotplug.2015.05.27a:  CPU-hotplug updates.
init.2015.05.27a:  Initialization/Kconfig updates.
tiny.2015.05.27a:  Updates to Tiny RCU.
torture.2015.05.27a:  Torture-testing updates.
2015-05-27 13:00:49 -07:00
Milos Vyletel ed38446424 documentation: State that rcu_dereference() reloads pointer
Make a note stating that repeated calls of rcu_dereference() may not
return the same pointer if update happens while in critical section.

Reported-by: Jeff Haran <jeff.haran@citrix.com>
Signed-off-by: Milos Vyletel <milos@redhat.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-05-27 12:57:28 -07:00
Paul E. McKenney ee7c29be36 documentation: Update rcu_dereference.txt based on WG21 discussions
This commit provides another caveat for the care and feeding of pointers
returned by rcu_dereference() that was pointed out in discussions within
the C++ standards committee.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
2015-05-27 12:57:28 -07:00
Paul E. McKenney cf9fbf8017 documentation: RCU-protected array indexes no longer supported
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-05-27 12:56:17 -07:00
Paul E. McKenney 78e691f4ae Merge branches 'doc.2015.01.07a', 'fixes.2015.01.15a', 'preempt.2015.01.06a', 'srcu.2015.01.06a', 'stall.2015.01.16a' and 'torture.2015.01.11a' into HEAD
doc.2015.01.07a: Documentation updates.
fixes.2015.01.15a: Miscellaneous fixes.
preempt.2015.01.06a: Changes to handling of lists of preempted tasks.
srcu.2015.01.06a: SRCU updates.
stall.2015.01.16a: RCU CPU stall-warning updates and fixes.
torture.2015.01.11a: RCU torture-test updates and fixes.
2015-01-15 23:34:34 -08:00
Paul E. McKenney fb81a44b88 rcu: Add GP-kthread-starvation checks to CPU stall warnings
This commit adds a message that is printed if the relevant grace-period
kthread has not been able to run for the two seconds preceding the
stall warning.  (The two seconds is double the maximum interval between
successive bouts of quiescent-state forcing.)

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2015-01-15 23:33:15 -08:00
Paul E. McKenney 5cd37193ce rcu: Make cond_resched_rcu_qs() apply to normal RCU flavors
Although cond_resched_rcu_qs() only applies to TASKS_RCU, it is used
in places where it would be useful for it to apply to the normal RCU
flavors, rcu_preempt, rcu_sched, and rcu_bh.  This is especially the
case for workloads that aggressively overload the system, particularly
those that generate large numbers of RCU updates on systems running
NO_HZ_FULL CPUs.  This commit therefore communicates quiescent states
from cond_resched_rcu_qs() to the normal RCU flavors.

Note that it is unfortunately necessary to leave the old ->passed_quiesce
mechanism in place to allow quiescent states that apply to only one
flavor to be recorded.  (Yes, we could decrement ->rcu_qs_ctr_snap in
that case, but that is not so good for debugging of RCU internals.)
In addition, if one of the RCU flavor's grace period has stalled, this
will invoke rcu_momentary_dyntick_idle(), resulting in a heavy-weight
quiescent state visible from other CPUs.

Reported-by: Sasha Levin <sasha.levin@oracle.com>
Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Merge commit from Sasha Levin fixing a bug where __this_cpu()
  was used in preemptible code. ]
2015-01-15 23:33:14 -08:00