- Core:
- The timer_shutdown[_sync]() infrastructure:
Tearing down timers can be tedious when there are circular
dependencies to other things which need to be torn down. A prime
example is timer and workqueue where the timer schedules work and the
work arms the timer.
What needs to prevented is that pending work which is drained via
destroy_workqueue() does not rearm the previously shutdown
timer. Nothing in that shutdown sequence relies on the timer being
functional.
The conclusion was that the semantics of timer_shutdown_sync() should
be:
- timer is not enqueued
- timer callback is not running
- timer cannot be rearmed
Preventing the rearming of shutdown timers is done by discarding rearm
attempts silently. A warning for the case that a rearm attempt of a
shutdown timer is detected would not be really helpful because it's
entirely unclear how it should be acted upon. The only way to address
such a case is to add 'if (in_shutdown)' conditionals all over the
place. This is error prone and in most cases of teardown not required
all.
- The real fix for the bluetooth HCI teardown based on
timer_shutdown_sync().
A larger scale conversion to timer_shutdown_sync() is work in
progress.
- Consolidation of VDSO time namespace helper functions
- Small fixes for timer and timerqueue
- Drivers:
- Prevent integer overflow on the XGene-1 TVAL register which causes
an never ending interrupt storm.
- The usual set of new device tree bindings
- Small fixes and improvements all over the place
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Merge tag 'timers-core-2022-12-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer updates from Thomas Gleixner:
"Updates for timers, timekeeping and drivers:
Core:
- The timer_shutdown[_sync]() infrastructure:
Tearing down timers can be tedious when there are circular
dependencies to other things which need to be torn down. A prime
example is timer and workqueue where the timer schedules work and
the work arms the timer.
What needs to prevented is that pending work which is drained via
destroy_workqueue() does not rearm the previously shutdown timer.
Nothing in that shutdown sequence relies on the timer being
functional.
The conclusion was that the semantics of timer_shutdown_sync()
should be:
- timer is not enqueued
- timer callback is not running
- timer cannot be rearmed
Preventing the rearming of shutdown timers is done by discarding
rearm attempts silently.
A warning for the case that a rearm attempt of a shutdown timer is
detected would not be really helpful because it's entirely unclear
how it should be acted upon. The only way to address such a case is
to add 'if (in_shutdown)' conditionals all over the place. This is
error prone and in most cases of teardown not required all.
- The real fix for the bluetooth HCI teardown based on
timer_shutdown_sync().
A larger scale conversion to timer_shutdown_sync() is work in
progress.
- Consolidation of VDSO time namespace helper functions
- Small fixes for timer and timerqueue
Drivers:
- Prevent integer overflow on the XGene-1 TVAL register which causes
an never ending interrupt storm.
- The usual set of new device tree bindings
- Small fixes and improvements all over the place"
* tag 'timers-core-2022-12-10' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (34 commits)
dt-bindings: timer: renesas,cmt: Add r8a779g0 CMT support
dt-bindings: timer: renesas,tmu: Add r8a779g0 support
clocksource/drivers/arm_arch_timer: Use kstrtobool() instead of strtobool()
clocksource/drivers/timer-ti-dm: Fix missing clk_disable_unprepare in dmtimer_systimer_init_clock()
clocksource/drivers/timer-ti-dm: Clear settings on probe and free
clocksource/drivers/timer-ti-dm: Make timer_get_irq static
clocksource/drivers/timer-ti-dm: Fix warning for omap_timer_match
clocksource/drivers/arm_arch_timer: Fix XGene-1 TVAL register math error
clocksource/drivers/timer-npcm7xx: Enable timer 1 clock before use
dt-bindings: timer: nuvoton,npcm7xx-timer: Allow specifying all clocks
dt-bindings: timer: rockchip: Add rockchip,rk3128-timer
clockevents: Repair kernel-doc for clockevent_delta2ns()
clocksource/drivers/ingenic-ost: Define pm functions properly in platform_driver struct
clocksource/drivers/sh_cmt: Access registers according to spec
vdso/timens: Refactor copy-pasted find_timens_vvar_page() helper into one copy
Bluetooth: hci_qca: Fix the teardown problem for real
timers: Update the documentation to reflect on the new timer_shutdown() API
timers: Provide timer_shutdown[_sync]()
timers: Add shutdown mechanism to the internal functions
timers: Split [try_to_]del_timer[_sync]() to prepare for shutdown mode
...
In order to make sure that a timer is not re-armed after it is stopped
before freeing, a new shutdown state is added to the timer code. The API
timer_shutdown_sync() and timer_shutdown() must be called before the
object that holds the timer can be freed.
Update the documentation to reflect this new workflow.
[ tglx: Updated to the new semantics and updated the zh_CN version ]
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Link: https://lore.kernel.org/r/20221110064147.712934793@goodmis.org
Link: https://lore.kernel.org/r/20221123201625.375284489@linutronix.de
Adjust to the new preferred function names.
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Link: https://lore.kernel.org/r/20221123201625.075320635@linutronix.de
This commit updates listRCU.txt to reflect RCU additions and changes
over the past few years.
[ paulmck: Apply kernel test robot feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Although RCU can in theory be used to protect array indexes in a manner
similar to the way it protects pointers, doing so is extremely risky
because of the huge number of optimizations that modern compilers can
apply to integral types.
For but one example, if your code can be configured such that your array
contains only a single element, then indexing that array with any integer
other than zero invokes undefined behavior, which in turn means that
the compiler is within its rights to assume (without checking!) that any
integer used as an index to that array has the value zero. Therefore,
the compiler can index the array with the constant zero, which breaks
any dependencies that might have otherwise existed between the time the
actual value was loaded and the time that the array was indexed.
This commit therefore removes the arrayRCU.rst file that describes how
to go about carrying dependencies through array indexes.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
but a few significant changes even so:
- A complete rewriting of the top-level index.rst file, which mostly
reflects itself in a redone top page in the HTML-rendered docs. The hope
is that the new organization will be a friendlier starting point for
both users and developers.
- Some math-rendering improvements.
- A coding-style.rst update on the use of BUG() and WARN()
- A big maintainer-PHP guide update.
- Some code-of-conduct updates
- More Chinese translation work
Plus the usual pile of typo fixes, corrections, and updates.
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Merge tag 'docs-6.1' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"There's not a huge amount of activity in the docs tree this time
around, but a few significant changes even so:
- A complete rewriting of the top-level index.rst file, which mostly
reflects itself in a redone top page in the HTML-rendered docs. The
hope is that the new organization will be a friendlier starting
point for both users and developers.
- Some math-rendering improvements.
- A coding-style.rst update on the use of BUG() and WARN()
- A big maintainer-PHP guide update.
- Some code-of-conduct updates
- More Chinese translation work
Plus the usual pile of typo fixes, corrections, and updates"
* tag 'docs-6.1' of git://git.lwn.net/linux: (66 commits)
checkpatch: warn on usage of VM_BUG_ON() and other BUG variants
coding-style.rst: document BUG() and WARN() rules ("do not crash the kernel")
Documentation: devres: add missing IO helper
Documentation: devres: update IRQ helper
Documentation/mm: modify page_referenced to folio_referenced
Documentation/CoC: Reflect current CoC interpretation and practices
docs/doc-guide: Add documentation on SPHINX_IMGMATH
docs: process/5.Posting.rst: clarify use of Reported-by: tag
docs, kprobes: Fix the wrong location of Kprobes
docs: add a man-pages link to the front page
docs: put atomic*.txt and memory-barriers.txt into the core-api book
docs: move asm-annotations.rst into core-api
docs: remove some index.rst cruft
docs: reconfigure the HTML left column
docs: Rewrite the front page
docs: promote the title of process/index.rst
Documentation: devres: add missing SPI helper
Documentation: devres: add missing PINCTRL helpers
docs: hugetlbpage.rst: fix a typo of hugepage size
docs/zh_CN: Add new translation of admin-guide/bootconfig.rst
...
This patch adds LWN articles about RCU APIs which were released in 2019.
Also, HTTP URLs are replaced by HTTPS.
Signed-off-by: Shao-Tse Hung <ccs100203@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Because the SLAB_TYPESAFE_BY_RCU code does not zero pages that are
to be broken up into slabs, the memory returned by kmem_cache_alloc()
must be fully initialized, including any spinlocks included in the newly
allocated structure. This means that readers attempting to look up an
SLAB_TYPESAFE_BY_RCU object must use a reference-counting approach.
A spinlock may be acquired only after a reference is obtained, which
prevents that object from being passed to kmem_struct_free(), but only
while that reference continues to be held.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit updates the rcu_access_pointer() advice, noting that its
return value should not be assigned to a local variable, and also noting
that there is little point in using rcu_access_pointer() within an RCU
read-side critical section.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The rcu_access_pointer() macro does not consult lockdep by design because
it is intended to be used outside of RCU read-side critical sections.
This commit therefore makes a separate list for it in whatisRCU.rst.
Similarly, RCU_LOCKDEP_WARN(), rcu_sleep_check(), and RCU_NONIDLE()
do not do anything with pointer access. This commit therefore creates
a separate utility-API list for them.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The checklist.rst document advises periodic synchronize_rcu() invocations
to prevent callback flooding. However, rcu_barrier() is often a better
choice. This commit therefore adds words to this effect.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The current checklist.rst file correctly notes that RCU callbacks execute
in BH context, and cannot block. This commit adds words advising people
needing callbacks to block to use workqueues, for example, by replacing
call_rcu() with queue_rcu_work().
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit updates checklist.rst to emphasize the need for explicit
markers for RCU read-side critical sections.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Some eqs functions are now only used internally by context tracking, so
their public declarations can be removed.
Also middle functions such as rcu_user_*() and rcu_idle_*()
which now directly call to rcu_eqs_enter() and rcu_eqs_exit() can be
wiped out as well.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Uladzislau Rezki <uladzislau.rezki@sony.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicolas Saenz Julienne <nsaenz@kernel.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Cc: Yu Liao <liaoyu15@huawei.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Paul Gortmaker<paul.gortmaker@windriver.com>
Cc: Alex Belits <abelits@marvell.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Tested-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
The RCU dynticks counter is going to be merged into the context tracking
subsystem. Prepare with moving the NMI extended quiescent states
entrypoints to context tracking. For now those are dumb redirection to
existing RCU calls.
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Uladzislau Rezki <uladzislau.rezki@sony.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicolas Saenz Julienne <nsaenz@kernel.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Cc: Yu Liao <liaoyu15@huawei.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Paul Gortmaker<paul.gortmaker@windriver.com>
Cc: Alex Belits <abelits@marvell.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Tested-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
The RCU dynticks counter is going to be merged into the context tracking
subsystem. Prepare with moving the IRQ extended quiescent states
entrypoints to context tracking. For now those are dumb redirection to
existing RCU calls.
[ paulmck: Apply Stephen Rothwell feedback from -next. ]
[ paulmck: Apply Nathan Chancellor feedback. ]
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Uladzislau Rezki <uladzislau.rezki@sony.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicolas Saenz Julienne <nsaenz@kernel.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Cc: Yu Liao <liaoyu15@huawei.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Paul Gortmaker<paul.gortmaker@windriver.com>
Cc: Alex Belits <abelits@marvell.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Tested-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
The RCU dynticks counter is going to be merged into the context tracking
subsystem. Start with moving the idle extended quiescent states
entrypoints to context tracking. For now those are dumb redirections to
existing RCU calls.
[ paulmck: Apply kernel test robot feedback. ]
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Uladzislau Rezki <uladzislau.rezki@sony.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicolas Saenz Julienne <nsaenz@kernel.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Cc: Yu Liao <liaoyu15@huawei.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Paul Gortmaker<paul.gortmaker@windriver.com>
Cc: Alex Belits <abelits@marvell.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Tested-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Currently both expedited and regular grace period stall warnings use
a single timeout value that with units of seconds. However, recent
Android use cases problem require a sub-100-millisecond expedited RCU CPU
stall warning. Given that expedited RCU grace periods normally complete
in far less than a single millisecond, especially for small systems,
this is not unreasonable.
Therefore introduce the CONFIG_RCU_EXP_CPU_STALL_TIMEOUT kernel
configuration that defaults to 20 msec on Android and remains the same
as that of the non-expedited stall warnings otherwise. It also can be
changed in run-time via: /sys/.../parameters/rcu_exp_cpu_stall_timeout.
[ paulmck: Default of zero to use CONFIG_RCU_STALL_TIMEOUT. ]
Signed-off-by: Uladzislau Rezki <uladzislau.rezki@sony.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The RCU documentation contains old-style cross references which
do not follow the best practices outlined in doc-guide/sphinx.rst.
In addition, some of the cross references use URLs that should be replaced
by pathnames.
Update all of these cross references and adjust the surrounding words.
Summary of changes:
- out-of-date plaintext file names (*.txt) -> *.rst
- references by :ref: tags -> path names of *.rst
* use relative paths to .rst files under the RCU/ subdirectory
* use abs paths of Documentation/xxx for other .rst files
- references by URL under https://www.kernel.org/ -> paths of *.rst
- adjust surrounding words of some of updated references.
Note:
The automarkup.py script interprets references via "*.txt" as if they
were via "*.rst", so the *.txt -> *.rst changes should be regarded as
cleanups rather than bug fixes.
Cc: rcu@vger.kernel.org
Cc: linux-doc@vger.kernel.org
Tested-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit belatedly adds documentation of Tasks Rude RCU and Tasks
Trace RCU to RCU's requirements document.
Tested-by: Bagas Sanjaya <bagasdotme@gmail.com>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
All of the uses of CONFIG_RCU_FAST_NO_HZ=y that I have seen involve
systems with RCU callbacks offloaded. In this situation, all that this
Kconfig option does is slow down idle entry/exit with an additional
allways-taken early exit. If this is the only use case, then this
Kconfig option nothing but an attractive nuisance that needs to go away.
This commit therefore removes the RCU_FAST_NO_HZ Kconfig option.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
On Ubuntu Focal, strings in some of SVG files under
Documentation/RCU/Design can not be rendered properly when
converted to PDF.
Ubuntu releases since Focal and Debian bullseye have trouble
with "Symbol" font-family in SVG files.
As those strings are mostly API names such as "READ_ONCE()",
"WRITE_ONCE(), "rcu_read_lock()", and so on, using a generic
monospace font-family should be a good alternative.
Substitute the font-family name by a simple sed pattern:
's/Symbol/monospace/g'
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The reader-writer-lock analogy is a useful way to think about RCU, but
it is not always applicable. It is useful to have other analogies to
work with, and particularly to emphasise that no single analogy is
perfect.
This patch add a "RCU as reference count" to the "what is RCU" document.
See https://lwn.net/Articles/872559/
[ paulmck: Apply Akira Yokosawa feedback. ]
Reviewed-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Invoking scripts/checkkconfigsymbols.py in the Linux-kernel source tree
located the following issues:
1. TREE_PREEMPT_RCU
Referencing files: arch/sh/configs/sdk7786_defconfig
It should now be CONFIG_PREEMPT_RCU. Except that the CONFIG_PREEMPT=y in
that same file implies CONFIG_PREEMPT_RCU=y. Therefore, delete the
CONFIG_TREE_PREEMPT_RCU=y line.
The reason is as follows:
In kernel/rcu/Kconfig, we have
config PREEMPT_RCU
bool
default y if PREEMPTION
https://www.kernel.org/doc/Documentation/kbuild/kconfig-language.txt says,
"The default value is only assigned to the config symbol if no other value
was set by the user (via the input prompt above)."
there is no prompt in config PREEMPT_RCU entry, so we are guaranteed to
get CONFIG_PREEMPT_RCU=y when CONFIG_PREEMPT is present.
2. RCU_CPU_STALL_INFO
Referencing files: arch/xtensa/configs/nommu_kc705_defconfig
The old Kconfig option RCU_CPU_STALL_INFO was removed by commit
75c27f119b ("rcu: Remove CONFIG_RCU_CPU_STALL_INFO"), and the kernel
now acts as if this Kconfig option was unconditionally enabled.
3. RCU_NOCB_CPU_ALL
Referencing files:
Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst
This is an old snapshot of the code. I update this from the real
rcu_prepare_for_idle() function in kernel/rcu/tree_plugin.h.
This change was tested by invoking "make htmldocs".
4. RCU_TORTURE_TESTS
Referencing files: kernel/rcu/rcutorture.c
Forward-progress checking conflicts with CPU-stall testing, so we should
complain at "modprobe rcutorture" when both are enabled.
Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit adds a bullet item noting that both deficiencies and surpluses
of calls to rcu_*_enter() and rcu_*_exit() can result in RCU CPU stall
warnings.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit calls out the possibility of self-detected stalls, adds new
messages, and calls out the use for stack traces.
Reported-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Add some missing critical pieces of explanation to understand the need
for full memory barriers throughout the whole grace period state machine,
thanks to Paul's explanations.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Neeraj Upadhyay <neeraju@codeaurora.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
[ paulmck: Adjust code block per Akira Yokosawa. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
To avoid the ``foo`` markup inside the `bar`__ hyperlink marker,
use the "replace" directive [1].
This should restore the intended appearance of the link.
Tested with sphinx versions 1.7.9 and 2.4.4.
[1]: https://docutils.sourceforge.io/docs/ref/rst/directives.html#replace
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
"-foo-" does not work as emphasis in ReST markdown.
Use "*foo*" instead.
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Pull RCU updates from Paul McKenney:
- Bitmap parsing support for "all" as an alias for all bits
- Documentation updates
- Miscellaneous fixes, including some that overlap into mm and lockdep
- kvfree_rcu() updates
- mem_dump_obj() updates, with acks from one of the slab-allocator
maintainers
- RCU NOCB CPU updates, including limited deoffloading
- SRCU updates
- Tasks-RCU updates
- Torture-test updates
* 'core-rcu-2021.07.04' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (78 commits)
tasks-rcu: Make show_rcu_tasks_gp_kthreads() be static inline
rcu-tasks: Make ksoftirqd provide RCU Tasks quiescent states
rcu: Add missing __releases() annotation
rcu: Remove obsolete rcu_read_unlock() deadlock commentary
rcu: Improve comments describing RCU read-side critical sections
rcu: Create an unrcu_pointer() to remove __rcu from a pointer
srcu: Early test SRCU polling start
rcu: Fix various typos in comments
rcu/nocb: Unify timers
rcu/nocb: Prepare for fine-grained deferred wakeup
rcu/nocb: Only cancel nocb timer if not polling
rcu/nocb: Delete bypass_timer upon nocb_gp wakeup
rcu/nocb: Cancel nocb_timer upon nocb_gp wakeup
rcu/nocb: Allow de-offloading rdp leader
rcu/nocb: Directly call __wake_nocb_gp() from bypass timer
rcu: Don't penalize priority boosting when there is nothing to boost
rcu: Point to documentation of ordering guarantees
rcu: Make rcu_gp_cleanup() be noinline for tracing
rcu: Restrict RCU_STRICT_GRACE_PERIOD to at most four CPUs
rcu: Make show_rcu_gp_kthreads() dump rcu_node structures blocking GP
...
This commit gives an example of non-obvious RCU reader/updater pairing
in the guise of the XDP feature in networking, which calls BPF programs
from network-driver NAPI (softirq) context.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210624160609.292325-4-toke@redhat.com
This commit clarifies which primitives readers can use given that the
corresponding updaters have made a specific choice. This commit also adds
this information for the various RCU Tasks flavors. While in the area, it
removes a paragraph that no longer applies in any straightforward manner.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210624160609.292325-3-toke@redhat.com
The three diagrams describing rcu_gp_init() all spuriously refer to
the same figure, probably due to a copy/paste issue. This commit fixes
these references.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The sentence defining the relationship of accesses before a grace
period to read-side accesses following that same grace period was
missing a small word: "not". This commit therefore adds it.
Reported-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit replaces "Steve" with the his real name, which is "Stephen".
Reported-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
- As promised, the minimum Sphinx version to build the docs is now 1.7,
and we have dropped support for Python 2 entirely. That allowed the
removal of a bunch of compatibility code.
- A set of treewide warning fixups from Mauro that I applied after it
became clear nobody else was going to deal with them.
- The automarkup mechanism can now create cross-references from relative
paths to RST files.
- More translations, typo fixes, and warning fixes.
No conflicts with any other tree as far as I know.
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Merge tag 'docs-5.12' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"It has been a relatively quiet cycle in docsland.
- As promised, the minimum Sphinx version to build the docs is now
1.7, and we have dropped support for Python 2 entirely. That
allowed the removal of a bunch of compatibility code.
- A set of treewide warning fixups from Mauro that I applied after it
became clear nobody else was going to deal with them.
- The automarkup mechanism can now create cross-references from
relative paths to RST files.
- More translations, typo fixes, and warning fixes"
* tag 'docs-5.12' of git://git.lwn.net/linux: (75 commits)
docs: kernel-hacking: be more civil
docs: Remove the Microsoft rhetoric
Documentation/admin-guide: kernel-parameters: Update nohlt section
doc/admin-guide: fix spelling mistake: "perfomance" -> "performance"
docs: Document cross-referencing using relative path
docs: Enable usage of relative paths to docs on automarkup
docs: thermal: fix spelling mistakes
Documentation: admin-guide: Update kvm/xen config option
docs: Make syscalls' helpers naming consistent
coding-style.rst: Avoid comma statements
Documentation: /proc/loadavg: add 3 more field descriptions
Documentation/submitting-patches: Add blurb about backtraces in commit messages
Docs: drop Python 2 support
Move our minimum Sphinx version to 1.7
Documentation: input: define ABS_PRESSURE/ABS_MT_PRESSURE resolution as grams
scripts/kernel-doc: add internal hyperlink to DOC: sections
Update Documentation/admin-guide/sysctl/fs.rst
docs: Update DTB format references
docs: zh_CN: add iio index.rst translation
docs/zh_CN: add iio ep93xx_adc.rst translation
...
- Documentation updates.
- Miscellaneous fixes.
- kfree_rcu() updates: Addition of mem_dump_obj() to provide allocator return
addresses to more easily locate bugs. This has a couple of RCU-related commits,
but is mostly MM. Was pulled in with akpm's agreement.
- Per-callback-batch tracking of numbers of callbacks,
which enables better debugging information and smarter
reactions to large numbers of callbacks.
- The first round of changes to allow CPUs to be runtime switched from and to
callback-offloaded state.
- CONFIG_PREEMPT_RT-related changes.
- RCU CPU stall warning updates.
- Addition of polling grace-period APIs for SRCU.
- Torture-test and torture-test scripting updates, including a "torture everything"
script that runs rcutorture, locktorture, scftorture, rcuscale, and refscale.
Plus does an allmodconfig build.
- nolibc fixes for the torture tests
Signed-off-by: Ingo Molnar <mingo@kernel.org>
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Merge tag 'core-rcu-2021-02-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull RCU updates from Ingo Molnar:
"These are the latest RCU updates for v5.12:
- Documentation updates.
- Miscellaneous fixes.
- kfree_rcu() updates: Addition of mem_dump_obj() to provide
allocator return addresses to more easily locate bugs. This has a
couple of RCU-related commits, but is mostly MM. Was pulled in with
akpm's agreement.
- Per-callback-batch tracking of numbers of callbacks, which enables
better debugging information and smarter reactions to large numbers
of callbacks.
- The first round of changes to allow CPUs to be runtime switched
from and to callback-offloaded state.
- CONFIG_PREEMPT_RT-related changes.
- RCU CPU stall warning updates.
- Addition of polling grace-period APIs for SRCU.
- Torture-test and torture-test scripting updates, including a
"torture everything" script that runs rcutorture, locktorture,
scftorture, rcuscale, and refscale. Plus does an allmodconfig
build.
- nolibc fixes for the torture tests"
* tag 'core-rcu-2021-02-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (130 commits)
percpu_ref: Dump mem_dump_obj() info upon reference-count underflow
rcu: Make call_rcu() print mem_dump_obj() info for double-freed callback
mm: Make mem_obj_dump() vmalloc() dumps include start and length
mm: Make mem_dump_obj() handle vmalloc() memory
mm: Make mem_dump_obj() handle NULL and zero-sized pointers
mm: Add mem_dump_obj() to print source of memory block
tools/rcutorture: Fix position of -lgcc in mkinitrd.sh
tools/nolibc: Fix position of -lgcc in the documented example
tools/nolibc: Emit detailed error for missing alternate syscall number definitions
tools/nolibc: Remove incorrect definitions of __ARCH_WANT_*
tools/nolibc: Get timeval, timespec and timezone from linux/time.h
tools/nolibc: Implement poll() based on ppoll()
tools/nolibc: Implement fork() based on clone()
tools/nolibc: Make getpgrp() fall back to getpgid(0)
tools/nolibc: Make dup2() rely on dup3() when available
tools/nolibc: Add the definition for dup()
rcutorture: Add rcutree.use_softirq=0 to RUDE01 and TASKS01
torture: Maintain torture-specific set of CPUs-online books
torture: Clean up after torture-test CPU hotplugging
rcutorture: Make object_debug also double call_rcu() heap object
...
Pull RCU updates from Paul E. McKenney:
- Documentation updates.
- Miscellaneous fixes.
- kfree_rcu() updates: Addition of mem_dump_obj() to provide allocator return
addresses to more easily locate bugs. This has a couple of RCU-related commits,
but is mostly MM. Was pulled in with akpm's agreement.
- Per-callback-batch tracking of numbers of callbacks,
which enables better debugging information and smarter
reactions to large numbers of callbacks.
- The first round of changes to allow CPUs to be runtime switched from and to
callback-offloaded state.
- CONFIG_PREEMPT_RT-related changes.
- RCU CPU stall warning updates.
- Addition of polling grace-period APIs for SRCU.
- Torture-test and torture-test scripting updates, including a "torture everything"
script that runs rcutorture, locktorture, scftorture, rcuscale, and refscale.
Plus does an allmodconfig build.
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The "oprofile" user-space tools don't use the kernel OPROFILE support
any more, and haven't in a long time. User-space has been converted to
the perf interfaces.
Remove kernel's old oprofile support.
Suggested-by: Christoph Hellwig <hch@infradead.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Robert Richter <rric@kernel.org>
Acked-by: Paul E. McKenney <paulmck@kernel.org> #RCU
Acked-by: William Cohen <wcohen@redhat.com>
Acked-by: Al Viro <viro@zeniv.linux.org.uk>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Replace the lkml.org links with lore to better use a single source
that's more likely to stay available long-term.
Done by bash script:
cvt_lkml_to_lore ()
{
tmpfile=$(mktemp ./.cvt_links.XXXXXXX)
header=$(echo $1 | sed 's@/lkml/@/lkml/headers/@')
wget -qO - $header > $tmpfile
if [[ $? == 0 ]] ; then
link=$(grep -i '^Message-Id:' $tmpfile | head -1 | \
sed -r -e 's/^\s*Message-Id:\s*<\s*//' -e 's/\s*>\s*$//' -e 's@^@https://lore.kernel.org/r/@')
# echo "testlink: $link"
if [ -n "$link" ] ; then
wget -qO - $link > /dev/null
if [[ $? == 0 ]] ; then
echo $link
fi
fi
fi
rm -f $tmpfile
}
git grep -P -o "\bhttps?://(?:www.)?lkml.org/lkml[\/\w]+" $@ |
while read line ; do
echo $line
file=$(echo $line | cut -f1 -d':')
link=$(echo $line | cut -f2- -d':')
newlink=$(cvt_lkml_to_lore $link)
if [[ -n "$newlink" ]] ; then
sed -i -e "s#\b$link\b#$newlink#" $file
fi
done
Link: https://lore.kernel.org/patchwork/patch/1265849/#1462688
Signed-off-by: Joe Perches <joe@perches.com>
Link: https://lore.kernel.org/r/77cdb7f32cfb087955bfc3600b86c40bed5d4104.camel@perches.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
For a new grace period request, the RCU GP kthread transitions through
following states:
a. [RCU_GP_WAIT_GPS] -> [RCU_GP_DONE_GPS]
The RCU_GP_WAIT_GPS state is where the GP kthread waits for a request
for a new GP. Once it receives a request (for example, when a new RCU
callback is queued), the GP kthread transitions to RCU_GP_DONE_GPS.
b. [RCU_GP_DONE_GPS] -> [RCU_GP_ONOFF]
Grace period initialization starts in rcu_gp_init(), which records the
start of new GP in rcu_state.gp_seq and transitions to RCU_GP_ONOFF.
c. [RCU_GP_ONOFF] -> [RCU_GP_INIT]
The purpose of the RCU_GP_ONOFF state is to apply the online/offline
information that was buffered for any CPUs that recently came online or
went offline. This state is maintained in per-leaf rcu_node bitmasks,
with the buffered state in ->qsmaskinitnext and the state for the upcoming
GP in ->qsmaskinit. At the end of this RCU_GP_ONOFF state, each bit in
->qsmaskinit will correspond to a CPU that must pass through a quiescent
state before the upcoming grace period is allowed to complete.
However, a leaf rcu_node structure with an all-zeroes ->qsmaskinit
cannot necessarily be ignored. In preemptible RCU, there might well be
tasks still in RCU read-side critical sections that were first preempted
while running on one of the CPUs managed by this structure. Such tasks
will be queued on this structure's ->blkd_tasks list. Only after this
list fully drains can this leaf rcu_node structure be ignored, and even
then only if none of its CPUs have come back online in the meantime.
Once that happens, the ->qsmaskinit masks further up the tree will be
updated to exclude this leaf rcu_node structure.
Once the ->qsmaskinitnext and ->qsmaskinit fields have been updated
as needed, the GP kthread transitions to RCU_GP_INIT.
d. [RCU_GP_INIT] -> [RCU_GP_WAIT_FQS]
The purpose of the RCU_GP_INIT state is to copy each ->qsmaskinit to
the ->qsmask field within each rcu_node structure. This copying is done
breadth-first from the root to the leaves. Why not just copy directly
from ->qsmaskinitnext to ->qsmask? Because the ->qsmaskinitnext masks
can change in the meantime as additional CPUs come online or go offline.
Such changes would result in inconsistencies in the ->qsmask fields up and
down the tree, which could in turn result in too-short grace periods or
grace-period hangs. These issues are avoided by snapshotting the leaf
rcu_node structures' ->qsmaskinitnext fields into their ->qsmaskinit
counterparts, generating a consistent set of ->qsmaskinit fields
throughout the tree, and only then copying these consistent ->qsmaskinit
fields to their ->qsmask counterparts.
Once this initialization step is complete, the GP kthread transitions
to RCU_GP_WAIT_FQS, where it waits to do a force-quiescent-state scan
on the one hand or for the end of the grace period on the other.
e. [RCU_GP_WAIT_FQS] -> [RCU_GP_DOING_FQS]
The RCU_GP_WAIT_FQS state waits for one of three things: (1) An
explicit request to do a force-quiescent-state scan, (2) The end of
the grace period, or (3) A short interval of time, after which it
will do a force-quiescent-state (FQS) scan. The explicit request can
come from rcutorture or from any CPU that has too many RCU callbacks
queued (see the qhimark kernel parameter and the RCU_GP_FLAG_OVLD
flag). The aforementioned "short period of time" is specified by the
jiffies_till_first_fqs boot parameter for a given grace period's first
FQS scan and by the jiffies_till_next_fqs for later FQS scans.
Either way, once the wait is over, the GP kthread transitions to
RCU_GP_DOING_FQS.
f. [RCU_GP_DOING_FQS] -> [RCU_GP_CLEANUP]
The RCU_GP_DOING_FQS state performs an FQS scan. Each such scan carries
out two functions for any CPU whose bit is still set in its leaf rcu_node
structure's ->qsmask field, that is, for any CPU that has not yet reported
a quiescent state for the current grace period:
i. Report quiescent states on behalf of CPUs that have been observed
to be idle (from an RCU perspective) since the beginning of the
grace period.
ii. If the current grace period is too old, take various actions to
encourage holdout CPUs to pass through quiescent states, including
enlisting the aid of any calls to cond_resched() and might_sleep(),
and even including IPIing the holdout CPUs.
These checks are skipped for any leaf rcu_node structure with a all-zero
->qsmask field, however such structures are subject to RCU priority
boosting if there are tasks on a given structure blocking the current
grace period. The end of the grace period is detected when the root
rcu_node structure's ->qsmask is zero and when there are no longer any
preempted tasks blocking the current grace period. (No, this last check
is not redundant. To see this, consider an rcu_node tree having exactly
one structure that serves as both root and leaf.)
Once the end of the grace period is detected, the GP kthread transitions
to RCU_GP_CLEANUP.
g. [RCU_GP_CLEANUP] -> [RCU_GP_CLEANED]
The RCU_GP_CLEANUP state marks the end of grace period by updating the
rcu_state structure's ->gp_seq field and also all rcu_node structures'
->gp_seq field. As before, the rcu_node tree is traversed in breadth
first order. Once this update is complete, the GP kthread transitions
to the RCU_GP_CLEANED state.
i. [RCU_GP_CLEANED] -> [RCU_GP_INIT]
Once in the RCU_GP_CLEANED state, the GP kthread immediately transitions
into the RCU_GP_INIT state.
j. The role of timers.
If there is at least one idle CPU, and if timers are not firing, the
transition from RCU_GP_DOING_FQS to RCU_GP_CLEANUP will never happen.
Timers can fail to fire for a number of reasons, including issues in
timer configuration, issues in the timer framework, and failure to handle
softirqs (for example, when there is a storm of interrupts). Whatever the
reason, if the timers fail to fire, the GP kthread will never be awakened,
resulting in RCU CPU stall warnings and eventually in OOM.
However, an RCU CPU stall warning has a large number of potential causes,
as documented in Documentation/RCU/stallwarn.rst. This commit therefore
adds analysis to the RCU CPU stall-warning code to emit an additional
message if the cause of the stall is likely to be timer failure.
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
CONFIG_PREEMPTION is selected by CONFIG_PREEMPT and by CONFIG_PREEMPT_RT.
Both PREEMPT and PREEMPT_RT require the same functionality which today
depends on CONFIG_PREEMPT.
Update the documents and mention CONFIG_PREEMPTION. Spell out
CONFIG_PREEMPT_RT (instead PREEMPT_RT) since it is an option now.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
The PREEMPT_RT wiki moved from kernel.org to the Linux Foundation wiki.
The kernel.org wiki is read only.
This commit therefore updates the URL of the active PREEMPT_RT wiki.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Linus Torvalds