The consolidation of the debug code for mutex waiter intialization sets
waiter::ww_ctx to a poison value unconditionally. For regular mutexes this
is intended to catch the case where waiter_ww_ctx is dereferenced
accidentally.
For ww_mutex the poison value has to be overwritten either with a context
pointer or NULL for ww_mutexes without context.
The rework broke this as it made the store conditional on the context
pointer instead of the argument which signals whether ww_mutex code should
be compiled in or optiized out. As a result waiter::ww_ctx ends up with the
poison pointer for contextless ww_mutexes which causes a later dereference of
the poison pointer because it is != NULL.
Use the build argument instead so for ww_mutex the poison value is always
overwritten.
Fixes: c0afb0ffc0 ("locking/ww_mutex: Gather mutex_waiter initialization")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210819193030.zpwrpvvrmy7xxxiy@linutronix.de
Add the necessary defines, helpers and API functions for replacing struct mutex on
a PREEMPT_RT enabled kernel with an rtmutex based variant.
No functional change when CONFIG_PREEMPT_RT=n
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211305.081517417@linutronix.de
Split the W/W mutex helper functions out into a separate header file, so
they can be shared with a rtmutex based variant later.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.396893399@linutronix.de
Split the ww related part out into a helper function so it can be reused
for a rtmutex based ww_mutex implementation.
[ mingo: Fixed bisection failure. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.340166556@linutronix.de
The wait_lock of mutex is really a low level lock. Convert it to a
raw_spinlock like the wait_lock of rtmutex.
[ mingo: backmerged the test_lockup.c build fix by bigeasy. ]
Co-developed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211304.166863404@linutronix.de
Having two header files which contain just the non-debug and debug variants
is mostly waste of disc space and has no real value. Stick the debug
variants into the common mutex.h file as counterpart to the stubs for the
non-debug case.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20210815211303.995350521@linutronix.de
Yanfei reported that it is possible to loose HANDOFF when we race with
mutex_unlock() and end up setting HANDOFF on an unlocked mutex. At
that point anybody can steal it, losing HANDOFF in the process.
If this happens often enough, we can in fact starve the top waiter.
Solve this by folding the 'set HANDOFF' operation into the trylock
operation, such that either we acquire the lock, or it gets HANDOFF
set. This avoids having HANDOFF set on an unlocked mutex.
Reported-by: Yanfei Xu <yanfei.xu@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Yanfei Xu <yanfei.xu@windriver.com>
Link: https://lore.kernel.org/r/20210630154114.958507900@infradead.org
Yanfei reported that setting HANDOFF should not depend on recomputing
@first, only on @first state. Which would then give:
if (ww_ctx || !first)
first = __mutex_waiter_is_first(lock, &waiter);
if (first)
__mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
But because 'ww_ctx || !first' is basically 'always' and the test for
first is relatively cheap, omit that first branch entirely.
Reported-by: Yanfei Xu <yanfei.xu@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Reviewed-by: Yanfei Xu <yanfei.xu@windriver.com>
Link: https://lore.kernel.org/r/20210630154114.896786297@infradead.org
Change the type and name of task_struct::state. Drop the volatile and
shrink it to an 'unsigned int'. Rename it in order to find all uses
such that we can use READ_ONCE/WRITE_ONCE as appropriate.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20210611082838.550736351@infradead.org
When a interruptible mutex locker is interrupted by a signal
without acquiring this lock and removed from the wait queue.
if the mutex isn't contended enough to have a waiter
put into the wait queue again, the setting of the WAITER
bit will force mutex locker to go into the slowpath to
acquire the lock every time, so if the wait queue is empty,
the WAITER bit need to be clear.
Fixes: 040a0a3710 ("mutex: Add support for wound/wait style locks")
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Zqiang <qiang.zhang@windriver.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210517034005.30828-1-qiang.zhang@windriver.com
The use_ww_ctx flag is passed to mutex_optimistic_spin(), but the
function doesn't use it. The frequent use of the (use_ww_ctx && ww_ctx)
combination is repetitive.
In fact, ww_ctx should not be used at all if !use_ww_ctx. Simplify
ww_mutex code by dropping use_ww_ctx from mutex_optimistic_spin() an
clear ww_ctx if !use_ww_ctx. In this way, we can replace (use_ww_ctx &&
ww_ctx) by just (ww_ctx).
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Davidlohr Bueso <dbueso@suse.de>
Link: https://lore.kernel.org/r/20210316153119.13802-2-longman@redhat.com
There are not users of mutex_trylock_recursive() in tree as of
v5.11-rc7.
Remove it.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210210085248.219210-2-bigeasy@linutronix.de
This ended up causing some noise in places such as rxrpc running in softirq.
The warning is misleading in this case as the mutex trylock and unlock
operations are done within the same context; and therefore we need not
worry about the PI-boosting issues that comes along with no single-owner
lock guarantees.
While we don't want to support this in mutexes, there is no way out of
this yet; so lets get rid of the WARNs for now, as it is only fair to
code that has historically relied on non-preemptible softirq guarantees.
In addition, changing the lock type is also unviable: exclusive rwsems
have the same issue (just not the WARN_ON) and counting semaphores
would introduce a performance hit as mutexes are a lot more optimized.
This reverts:
a0855d24fc22: ("locking/mutex: Complain upon mutex API misuse in IRQ contexts")
Fixes: a0855d24fc22: ("locking/mutex: Complain upon mutex API misuse in IRQ contexts")
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Tested-by: David Howells <dhowells@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-afs@lists.infradead.org
Cc: linux-fsdevel@vger.kernel.org
Cc: will@kernel.org
Link: https://lkml.kernel.org/r/20191210220523.28540-1-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Add warning checks if mutex_trylock() or mutex_unlock() are used in
IRQ contexts, under CONFIG_DEBUG_MUTEXES=y.
While the mutex rules and semantics are explicitly documented, this allows
to expose any abusers and robustifies the whole thing.
While trylock and unlock are non-blocking, calling from IRQ context
is still forbidden (lock must be within the same context as unlock).
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dave@stgolabs.net
Link: https://lkml.kernel.org/r/20191025033634.3330-1-dave@stgolabs.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The patch moving bits into mutex.c was a little too much; by also
moving struct mutex_waiter a few less common CONFIGs would no longer
build.
Fixes: 5f35d5a66b ("locking/mutex: Make __mutex_owner static to mutex.c")
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
__mutex_owner() should only be used by the mutex api's.
So, to put this restiction let's move the __mutex_owner()
function definition from linux/mutex.h to mutex.c file.
There exist functions that uses __mutex_owner() like
mutex_is_locked() and mutex_trylock_recursive(), So
to keep legacy thing intact move them as well and
export them.
Move mutex_waiter structure also to keep it private to the
file.
Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: mingo@redhat.com
Cc: will@kernel.org
Link: https://lkml.kernel.org/r/1564585504-3543-1-git-send-email-mojha@codeaurora.org
An uninitialized/ zeroed mutex will go unnoticed because there is no
check for it. There is a magic check in the unlock's slowpath path which
might go unnoticed if the unlock happens in the fastpath.
Add a ->magic check early in the mutex_lock() and mutex_trylock() path.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190703092125.lsdf4gpsh2plhavb@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Convert the locking documents to ReST and add them to the
kernel development book where it belongs.
Most of the stuff here is just to make Sphinx to properly
parse the text file, as they're already in good shape,
not requiring massive changes in order to be parsed.
The conversion is actually:
- add blank lines and identation in order to identify paragraphs;
- fix tables markups;
- add some lists markups;
- mark literal blocks;
- adjust title markups.
At its new index.rst, let's add a :orphan: while this is not linked to
the main index.rst file, in order to avoid build warnings.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Federico Vaga <federico.vaga@vaga.pv.it>
Add SPDX license identifiers to all files which:
- Have no license information of any form
- Have EXPORT_.*_SYMBOL_GPL inside which was used in the
initial scan/conversion to ignore the file
These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:
GPL-2.0-only
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This is already done for us internally by the signal machinery.
Link: http://lkml.kernel.org/r/20181116002713.8474-2-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The following commit:
08295b3b5b ("Implement an algorithm choice for Wound-Wait mutexes")
introduced a reference in the documentation to a function that was
removed in an earlier commit.
It also forgot to remove a call to debug_mutex_add_waiter() which is now
unconditionally called by __mutex_add_waiter().
Fix those bugs.
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dri-devel@lists.freedesktop.org
Fixes: 08295b3b5b ("Implement an algorithm choice for Wound-Wait mutexes")
Link: http://lkml.kernel.org/r/20180903140708.2401-1-thellstrom@vmware.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The current Wound-Wait mutex algorithm is actually not Wound-Wait but
Wait-Die. Implement also Wound-Wait as a per-ww-class choice. Wound-Wait
is, contrary to Wait-Die a preemptive algorithm and is known to generate
fewer backoffs. Testing reveals that this is true if the
number of simultaneous contending transactions is small.
As the number of simultaneous contending threads increases, Wait-Wound
becomes inferior to Wait-Die in terms of elapsed time.
Possibly due to the larger number of held locks of sleeping transactions.
Update documentation and callers.
Timings using git://people.freedesktop.org/~thomash/ww_mutex_test
tag patch-18-06-15
Each thread runs 100000 batches of lock / unlock 800 ww mutexes randomly
chosen out of 100000. Four core Intel x86_64:
Algorithm #threads Rollbacks time
Wound-Wait 4 ~100 ~17s.
Wait-Die 4 ~150000 ~19s.
Wound-Wait 16 ~360000 ~109s.
Wait-Die 16 ~450000 ~82s.
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Co-authored-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
Make the WW mutex code more readable by adding comments, splitting up
functions and pointing out that we're actually using the Wait-Die
algorithm.
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Co-authored-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
On Wed, Mar 14, 2018 at 01:56:31PM -0700, Andrew Morton wrote:
> My memory is weak and our documentation is awful. What does
> mutex_lock_killable() actually do and how does it differ from
> mutex_lock_interruptible()?
Add kernel-doc for mutex_lock_killable() and mutex_lock_io(). Reword the
kernel-doc for mutex_lock_interruptible().
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: cl@linux.com
Cc: tj@kernel.org
Link: http://lkml.kernel.org/r/20180315115812.GA9949@bombadil.infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
There are a few issues on some kernel-doc markups that was
causing troubles with kernel-doc output on ReST format:
./kernel/futex.c:492: WARNING: Inline emphasis start-string without end-string.
./kernel/futex.c:1264: WARNING: Block quote ends without a blank line; unexpected unindent.
./kernel/futex.c:1721: WARNING: Block quote ends without a blank line; unexpected unindent.
./kernel/futex.c:2338: WARNING: Block quote ends without a blank line; unexpected unindent.
./kernel/futex.c:2426: WARNING: Block quote ends without a blank line; unexpected unindent.
./kernel/futex.c:2899: WARNING: Block quote ends without a blank line; unexpected unindent.
./kernel/futex.c:2972: WARNING: Block quote ends without a blank line; unexpected unindent.
Fix them.
No functional changes.
Acked-by: Darren Hart (VMware) <dvhart@infradead.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
We are going to split <linux/sched/debug.h> out of <linux/sched.h>, which
will have to be picked up from other headers and a couple of .c files.
Create a trivial placeholder <linux/sched/debug.h> file that just
maps to <linux/sched.h> to make this patch obviously correct and
bisectable.
Include the new header in the files that are going to need it.
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Fix up affected files that include this signal functionality via sched.h.
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
We are going to split <linux/sched/wake_q.h> out of <linux/sched.h>, which
will have to be picked up from other headers and a couple of .c files.
Create a trivial placeholder <linux/sched/wake_q.h> file that just
maps to <linux/sched.h> to make this patch obviously correct and
bisectable.
Include the new header in the files that are going to need it.
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Pull locking updates from Ingo Molnar:
"The main changes in this cycle were:
- Implement wraparound-safe refcount_t and kref_t types based on
generic atomic primitives (Peter Zijlstra)
- Improve and fix the ww_mutex code (Nicolai Hähnle)
- Add self-tests to the ww_mutex code (Chris Wilson)
- Optimize percpu-rwsems with the 'rcuwait' mechanism (Davidlohr
Bueso)
- Micro-optimize the current-task logic all around the core kernel
(Davidlohr Bueso)
- Tidy up after recent optimizations: remove stale code and APIs,
clean up the code (Waiman Long)
- ... plus misc fixes, updates and cleanups"
* 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (50 commits)
fork: Fix task_struct alignment
locking/spinlock/debug: Remove spinlock lockup detection code
lockdep: Fix incorrect condition to print bug msgs for MAX_LOCKDEP_CHAIN_HLOCKS
lkdtm: Convert to refcount_t testing
kref: Implement 'struct kref' using refcount_t
refcount_t: Introduce a special purpose refcount type
sched/wake_q: Clarify queue reinit comment
sched/wait, rcuwait: Fix typo in comment
locking/mutex: Fix lockdep_assert_held() fail
locking/rtmutex: Flip unlikely() branch to likely() in __rt_mutex_slowlock()
locking/rwsem: Reinit wake_q after use
locking/rwsem: Remove unnecessary atomic_long_t casts
jump_labels: Move header guard #endif down where it belongs
locking/atomic, kref: Implement kref_put_lock()
locking/ww_mutex: Turn off __must_check for now
locking/atomic, kref: Avoid more abuse
locking/atomic, kref: Use kref_get_unless_zero() more
locking/atomic, kref: Kill kref_sub()
locking/atomic, kref: Add kref_read()
locking/atomic, kref: Add KREF_INIT()
...
In commit:
659cf9f582 ("locking/ww_mutex: Optimize ww-mutexes by waking at most one waiter for backoff when acquiring the lock")
I replaced a comment with a lockdep_assert_held(). However it turns out
we hide that lock from lockdep for hysterical raisins, which results
in the assertion always firing.
Remove the old debug code as lockdep will easily spot the abuse it was
meant to catch, which will make the lock visible to lockdep and make
the assertion work as intended.
Reported-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicolai Haehnle <Nicolai.Haehnle@amd.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 659cf9f582 ("locking/ww_mutex: Optimize ww-mutexes by waking at most one waiter for backoff when acquiring the lock")
Link: http://lkml.kernel.org/r/20170117150609.GB32474@worktop
Signed-off-by: Ingo Molnar <mingo@kernel.org>
We sometimes end up propagating IO blocking through mutexes; however,
because there currently is no way of annotating mutex sleeps as
iowait, there are cases where iowait and /proc/stat:procs_blocked
report misleading numbers obscuring the actual state of the system.
This patch adds mutex_lock_io() so that mutex sleeps can be marked as
iowait in those cases.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: adilger.kernel@dilger.ca
Cc: jack@suse.com
Cc: kernel-team@fb.com
Cc: mingbo@fb.com
Cc: tytso@mit.edu
Link: http://lkml.kernel.org/r/1477673892-28940-4-git-send-email-tj@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Help catch cases where mutex_lock is used directly on w/w mutexes, which
otherwise result in the w/w tasks reading uninitialized data.
Signed-off-by: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maarten Lankhorst <dev@mblankhorst.nl>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dri-devel@lists.freedesktop.org
Link: http://lkml.kernel.org/r/1482346000-9927-12-git-send-email-nhaehnle@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Lock stealing is less beneficial for w/w mutexes since we may just end up
backing off if we stole from a thread with an earlier acquire stamp that
already holds another w/w mutex that we also need. So don't spin
optimistically unless we are sure that there is no other waiter that might
cause us to back off.
Median timings taken of a contention-heavy GPU workload:
Before:
real 0m52.946s
user 0m7.272s
sys 1m55.964s
After:
real 0m53.086s
user 0m7.360s
sys 1m46.204s
This particular workload still spends 20%-25% of CPU in mutex_spin_on_owner
according to perf, but my attempts to further reduce this spinning based on
various heuristics all lead to an increase in measured wall time despite
the decrease in sys time.
Signed-off-by: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maarten Lankhorst <dev@mblankhorst.nl>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dri-devel@lists.freedesktop.org
Link: http://lkml.kernel.org/r/1482346000-9927-11-git-send-email-nhaehnle@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
In the following scenario, thread #1 should back off its attempt to lock
ww1 and unlock ww2 (assuming the acquire context stamps are ordered
accordingly).
Thread #0 Thread #1
--------- ---------
successfully lock ww2
set ww1->base.owner
attempt to lock ww1
confirm ww1->ctx == NULL
enter mutex_spin_on_owner
set ww1->ctx
What was likely to happen previously is:
attempt to lock ww2
refuse to spin because
ww2->ctx != NULL
schedule()
detect thread #0 is off CPU
stop optimistic spin
return -EDEADLK
unlock ww2
wakeup thread #0
lock ww2
Now, we are more likely to see:
detect ww1->ctx != NULL
stop optimistic spin
return -EDEADLK
unlock ww2
successfully lock ww2
... because thread #1 will stop its optimistic spin as soon as possible.
The whole scenario is quite unlikely, since it requires thread #1 to get
between thread #0 setting the owner and setting the ctx. But since we're
idling here anyway, the additional check is basically free.
Found by inspection.
Signed-off-by: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maarten Lankhorst <dev@mblankhorst.nl>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dri-devel@lists.freedesktop.org
Link: http://lkml.kernel.org/r/1482346000-9927-10-git-send-email-nhaehnle@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Instead of inlining __mutex_lock_common() 5 times, once for each
{state,ww} variant. Reduce this to two, ww and !ww.
Then add __always_inline to mutex_optimistic_spin(), so that that will
get inlined all 4 remaining times, for all {waiter,ww} variants.
text data bss dec hex filename
6301 0 0 6301 189d defconfig-build/kernel/locking/mutex.o
4053 0 0 4053 fd5 defconfig-build/kernel/locking/mutex.o
4257 0 0 4257 10a1 defconfig-build/kernel/locking/mutex.o
This reduces total text size and better separates the ww and !ww mutex
code generation.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The wait list is sorted by stamp order, and the only waiting task that may
have to back off is the first waiter with a context.
The regular slow path does not have to wake any other tasks at all, since
all other waiters that would have to back off were either woken up when
the waiter was added to the list, or detected the condition before they
added themselves.
Median timings taken of a contention-heavy GPU workload:
Without this series:
real 0m59.900s
user 0m7.516s
sys 2m16.076s
With changes up to and including this patch:
real 0m52.946s
user 0m7.272s
sys 1m55.964s
Signed-off-by: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maarten Lankhorst <dev@mblankhorst.nl>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dri-devel@lists.freedesktop.org
Link: http://lkml.kernel.org/r/1482346000-9927-9-git-send-email-nhaehnle@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
While adding our task as a waiter, detect if another task should back off
because of us.
With this patch, we establish the invariant that the wait list contains
at most one (sleeping) waiter with ww_ctx->acquired > 0, and this waiter
will be the first waiter with a context.
Since only waiters with ww_ctx->acquired > 0 have to back off, this allows
us to be much more economical with wakeups.
Signed-off-by: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maarten Lankhorst <dev@mblankhorst.nl>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dri-devel@lists.freedesktop.org
Link: http://lkml.kernel.org/r/1482346000-9927-8-git-send-email-nhaehnle@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Add regular waiters in stamp order. Keep adding waiters that have no
context in FIFO order and take care not to starve them.
While adding our task as a waiter, back off if we detect that there is
a waiter with a lower stamp in front of us.
Make sure to call lock_contended even when we back off early.
For w/w mutexes, being first in the wait list is only stable when
taking the lock without a context. Therefore, the purpose of the first
flag is split into two: 'first' remains to indicate whether we want to
spin optimistically, while 'handoff' indicates that we should be
prepared to accept a handoff.
For w/w locking with a context, we always accept handoffs after the
first schedule(), to handle the following sequence of events:
1. Task #0 unlocks and hands off to Task #2 which is first in line
2. Task #1 adds itself in front of Task #2
3. Task #2 wakes up and must accept the handoff even though it is no
longer first in line
Signed-off-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: =?UTF-8?q?Nicolai=20H=C3=A4hnle?= <Nicolai.Haehnle@amd.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maarten Lankhorst <dev@mblankhorst.nl>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dri-devel@lists.freedesktop.org
Link: http://lkml.kernel.org/r/1482346000-9927-7-git-send-email-nhaehnle@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Keep the documentation in the header file since there is no good place
for it in mutex.c: there are two rather different implementations with
different EXPORT_SYMBOLs for each function.
Signed-off-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: =?UTF-8?q?Nicolai=20H=C3=A4hnle?= <Nicolai.Haehnle@amd.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maarten Lankhorst <dev@mblankhorst.nl>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dri-devel@lists.freedesktop.org
Link: http://lkml.kernel.org/r/1482346000-9927-6-git-send-email-nhaehnle@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
We will add a new field to struct mutex_waiter. This field must be
initialized for all waiters if any waiter uses the ww_use_ctx path.
So there is a trade-off: Keep ww_mutex locking without a context on
the faster non-use_ww_ctx path, at the cost of adding the
initialization to all mutex locks (including non-ww_mutexes), or avoid
the additional cost for non-ww_mutex locks, at the cost of adding
additional checks to the use_ww_ctx path.
We take the latter choice. It may be worth eliminating the users of
ww_mutex_lock(lock, NULL), but there are a lot of them.
Signed-off-by: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maarten Lankhorst <dev@mblankhorst.nl>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dri-devel@lists.freedesktop.org
Link: http://lkml.kernel.org/r/1482346000-9927-5-git-send-email-nhaehnle@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
The function will be re-used in subsequent patches.
Signed-off-by: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maarten Lankhorst <dev@mblankhorst.nl>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dri-devel@lists.freedesktop.org
Link: http://lkml.kernel.org/r/1482346000-9927-4-git-send-email-nhaehnle@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Sebastian Andrzej Siewior