linux.git/kernel/locking/rwbase_rt.c, branch v7.2-rc1

locking: Add contended_release tracepoint to sleepable locks

2026-06-11T11:41:25+00:00

Add the contended_release trace event. This tracepoint fires on the
holder side when a contended lock is released, complementing the
existing contention_begin/contention_end tracepoints which fire on the
waiter side.

This enables correlating lock hold time under contention with waiter
events by lock address.

Add trace_contended_release()/trace_call__contended_release() calls to
the slowpath unlock paths of sleepable locks: mutex, rtmutex, semaphore,
rwsem, percpu-rwsem, and RT-specific rwbase locks.

Where possible, trace_contended_release() fires before the lock is
released and before the waiter is woken. For some lock types, the
tracepoint fires after the release but before the wake. Making the
placement consistent across all lock types is not worth the added
complexity.

For reader/writer locks, the tracepoint fires for every reader releasing
while a writer is waiting, not only for the last reader.

Signed-off-by: Dmitry Ilvokhin 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Paul E. McKenney 
Acked-by: Usama Arif 
Link: https://patch.msgid.link/02f4f6c5ce6761e7f6587cf0ff2289d962ecddd4.1780506267.git.d@ilvokhin.com

locking/rwsem: Add context analysis

2026-03-08T10:06:53+00:00

Add compiler context analysis annotations.

Signed-off-by: Peter Zijlstra (Intel) 
Link: https://patch.msgid.link/20260306101417.GT1282955@noisy.programming.kicks-ass.net

locking/mutex: Remove wakeups from under mutex::wait_lock

2024-10-14T10:52:40+00:00

In preparation to nest mutex::wait_lock under rq::lock we need
to remove wakeups from under it.

Do this by utilizing wake_qs to defer the wakeup until after the
lock is dropped.

[Heavily changed after 55f036ca7e74 ("locking: WW mutex cleanup") and
08295b3b5bee ("locking: Implement an algorithm choice for Wound-Wait
mutexes")]
[jstultz: rebased to mainline, added extra wake_up_q & init
 to avoid hangs, similar to Connor's rework of this patch]

Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Juri Lelli 
Signed-off-by: John Stultz 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Metin Kaya 
Acked-by: Davidlohr Bueso 
Tested-by: K Prateek Nayak 
Tested-by: Metin Kaya 
Link: https://lore.kernel.org/r/20241009235352.1614323-2-jstultz@google.com

locking/rtmutex: Add a lockdep assert to catch potential nested blocking

2023-09-20T07:31:14+00:00

There used to be a BUG_ON(current->pi_blocked_on) in the lock acquisition
functions, but that vanished in one of the rtmutex overhauls.

Bring it back in form of a lockdep assert to catch code paths which take
rtmutex based locks with current::pi_blocked_on != NULL.

Reported-by: Crystal Wood 
Signed-off-by: Thomas Gleixner 
Signed-off-by: "Peter Zijlstra (Intel)" 
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20230908162254.999499-7-bigeasy@linutronix.de

locking/rtmutex: Use rt_mutex specific scheduler helpers

2023-09-20T07:31:13+00:00

Have rt_mutex use the rt_mutex specific scheduler helpers to avoid
recursion vs rtlock on the PI state.

[[ peterz: adapted to new names ]]

Reported-by: Crystal Wood 
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20230908162254.999499-6-bigeasy@linutronix.de

locking/rwbase: Mitigate indefinite writer starvation

2023-04-29T07:08:52+00:00

On PREEMPT_RT, rw_semaphore and rwlock_t locks are unfair to writers.
Readers can indefinitely acquire the lock unless the writer fully acquired
the lock, which might never happen if there is always a reader in the
critical section owning the lock.

Mel Gorman reported that since LTP-20220121 the dio_truncate test case
went from having 1 reader to having 16 readers and that number of readers
is sufficient to prevent the down_write ever succeeding while readers
exist. Eventually the test is killed after 30 minutes as a failure.

Mel proposed a timeout to limit how long a writer can be blocked until
the reader is forced into the slowpath.

Thomas argued that there is no added value by providing this timeout.  From
a PREEMPT_RT point of view, there are no critical rw_semaphore or rwlock_t
locks left where the reader must be preferred.

Mitigate indefinite writer starvation by forcing the READER into the
slowpath once the WRITER attempts to acquire the lock.

Reported-by: Mel Gorman 
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Thomas Gleixner 
Signed-off-by: Ingo Molnar 
Acked-by: Mel Gorman 
Link: https://lore.kernel.org/877cwbq4cq.ffs@tglx
Link: https://lore.kernel.org/r/20230321161140.HMcQEhHb@linutronix.de
Cc: Linus Torvalds

locking: Apply contention tracepoints in the slow path

2022-04-05T08:24:35+00:00

Adding the lock contention tracepoints in various lock function slow
paths.  Note that each arch can define spinlock differently, I only
added it only to the generic qspinlock for now.

Signed-off-by: Namhyung Kim 
Signed-off-by: Peter Zijlstra (Intel) 
Tested-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Link: https://lkml.kernel.org/r/20220322185709.141236-3-namhyung@kernel.org

locking/rwbase: Optimize rwbase_read_trylock

2021-10-07T11:51:07+00:00

Instead of a full barrier around the Rmw insn, micro-optimize
for weakly ordered archs such that we only provide the required
ACQUIRE semantics when taking the read lock.

Signed-off-by: Davidlohr Bueso 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Waiman Long 
Link: https://lkml.kernel.org/r/20210920052031.54220-2-dave@stgolabs.net

Merge branch 'tip/locking/urgent'

2021-10-07T11:51:06+00:00

Pull in dependencies.

rtmutex: Wake up the waiters lockless while dropping the read lock.

2021-10-01T11:57:52+00:00

The rw_semaphore and rwlock_t implementation both wake the waiter while
holding the rt_mutex_base::wait_lock acquired.
This can be optimized by waking the waiter lockless outside of the
locked section to avoid a needless contention on the
rt_mutex_base::wait_lock lock.

Extend rt_mutex_wake_q_add() to also accept task and state and use it in
__rwbase_read_unlock().

Suggested-by: Davidlohr Bueso 
Signed-off-by: Thomas Gleixner 
Signed-off-by: Sebastian Andrzej Siewior 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20210928150006.597310-3-bigeasy@linutronix.de