From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D3B9B26F293; Tue, 14 Apr 2026 23:09:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776208170; cv=none; b=qvPa0Dmd2Aosq44PtFhYfkhmeKDB1i7pL+qKmOurkMu88ThrBipmh+XHmfpAFnld662UsH36aamgzktyApczJAG0VGnBX31uRmvtGkTsMDXRYZZG99PWSc0o+xSRM+n7dTicQIkbG8eIXCNDVgb1L15Cwjne41DYIOnDgBiHDxs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776208170; c=relaxed/simple; bh=m0W/Ernt03ORrUvvuWlaV+yJl5KaCu8uMNwKRgnc1JU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=OdqAxGJ/15T2adqQiMymz/Kn0o4o174jffktMJw8yi3qRMCdlKfIS3xglpz1ve9MJfL0W4tx590wsa2fj/wAm7kraLeJbiQPP1+zRUd8szWA/UcpjKAI2HWtMhGYdwo2Dwsf4MKqmeiOJ+BIimk9o3yG4tVhX/Xj19YYbxd2KTY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=qBelCepT; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="qBelCepT" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6918DC19425; Tue, 14 Apr 2026 23:09:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776208170; bh=m0W/Ernt03ORrUvvuWlaV+yJl5KaCu8uMNwKRgnc1JU=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=qBelCepTc9lFdVUgh+o5h1aXWx6734PGrt1TsMYUW8hNHRDFGGvbQBnbL7dkpco6k FOWMq2sxkQ//wmRKXPFKM2vXXv6BS3Sv3GEPKQgc9sNlUbSKK0Z3Ea5TZwC/uq1yAx XmarXC3/Ng/MOmZpZtC2AlgJFzmvc9Ns3XgKRXeNVliCghDA1lZzITubKE4U5WMow4 aLNVnwqvUSMw7gjHi2mEqYtiDu3lfqxpFZHxsZI966VlBMLNFolgMJDx3pPmVkSeKs jkTzJ9lwTV80UFCo9VCmOvVlg94JahYcn8tZKQTzVofGTAOdvXmkjGvWtz5BmsTKPW 7sluvHMU/cwXg== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 0224ECE13BF; Tue, 14 Apr 2026 16:09:29 -0700 (PDT) Date: Tue, 14 Apr 2026 16:09:29 -0700 From: "Paul E. McKenney" To: Dmitry Ilvokhin Cc: Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng , Waiman Long , Thomas Bogendoerfer , Juergen Gross , Ajay Kaher , Alexey Makhalov , Broadcom internal kernel review list , Thomas Gleixner , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Arnd Bergmann , Dennis Zhou , Tejun Heo , Christoph Lameter , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, virtualization@lists.linux.dev, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH v4 3/5] locking: Add contended_release tracepoint to sleepable locks Message-ID: <2d2a6584-2b75-44e9-953e-e6244ff2abc9@paulmck-laptop> Reply-To: paulmck@kernel.org References: Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Mar 26, 2026 at 03:10:02PM +0000, Dmitry Ilvokhin wrote: > 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() 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 Looks plausible: Acked-by: Paul E. McKenney > --- > include/trace/events/lock.h | 17 +++++++++++++++++ > kernel/locking/mutex.c | 4 ++++ > kernel/locking/percpu-rwsem.c | 11 +++++++++++ > kernel/locking/rtmutex.c | 1 + > kernel/locking/rwbase_rt.c | 6 ++++++ > kernel/locking/rwsem.c | 10 ++++++++-- > kernel/locking/semaphore.c | 4 ++++ > 7 files changed, 51 insertions(+), 2 deletions(-) > > diff --git a/include/trace/events/lock.h b/include/trace/events/lock.h > index da978f2afb45..1ded869cd619 100644 > --- a/include/trace/events/lock.h > +++ b/include/trace/events/lock.h > @@ -137,6 +137,23 @@ TRACE_EVENT(contention_end, > TP_printk("%p (ret=%d)", __entry->lock_addr, __entry->ret) > ); > > +TRACE_EVENT(contended_release, > + > + TP_PROTO(void *lock), > + > + TP_ARGS(lock), > + > + TP_STRUCT__entry( > + __field(void *, lock_addr) > + ), > + > + TP_fast_assign( > + __entry->lock_addr = lock; > + ), > + > + TP_printk("%p", __entry->lock_addr) > +); > + > #endif /* _TRACE_LOCK_H */ > > /* This part must be outside protection */ > diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c > index 427187ff02db..6c2c9312eb8f 100644 > --- a/kernel/locking/mutex.c > +++ b/kernel/locking/mutex.c > @@ -997,6 +997,9 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne > wake_q_add(&wake_q, next); > } > > + if (trace_contended_release_enabled() && waiter) > + trace_contended_release(lock); > + > if (owner & MUTEX_FLAG_HANDOFF) > __mutex_handoff(lock, next); > > @@ -1194,6 +1197,7 @@ EXPORT_SYMBOL(ww_mutex_lock_interruptible); > > EXPORT_TRACEPOINT_SYMBOL_GPL(contention_begin); > EXPORT_TRACEPOINT_SYMBOL_GPL(contention_end); > +EXPORT_TRACEPOINT_SYMBOL_GPL(contended_release); > > /** > * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0 > diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c > index f3ee7a0d6047..46b5903989b8 100644 > --- a/kernel/locking/percpu-rwsem.c > +++ b/kernel/locking/percpu-rwsem.c > @@ -263,6 +263,9 @@ void percpu_up_write(struct percpu_rw_semaphore *sem) > { > rwsem_release(&sem->dep_map, _RET_IP_); > > + if (trace_contended_release_enabled() && wq_has_sleeper(&sem->waiters)) > + trace_contended_release(sem); > + > /* > * Signal the writer is done, no fast path yet. > * > @@ -292,6 +295,14 @@ EXPORT_SYMBOL_GPL(percpu_up_write); > void __percpu_up_read(struct percpu_rw_semaphore *sem) > { > lockdep_assert_preemption_disabled(); > + /* > + * After percpu_up_write() completes, rcu_sync_is_idle() can still > + * return false during the grace period, forcing readers into this > + * slowpath. Only trace when a writer is actually waiting for > + * readers to drain. > + */ > + if (trace_contended_release_enabled() && rcuwait_active(&sem->writer)) > + trace_contended_release(sem); > /* > * slowpath; reader will only ever wake a single blocked > * writer. > diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c > index ccaba6148b61..3db8a840b4e8 100644 > --- a/kernel/locking/rtmutex.c > +++ b/kernel/locking/rtmutex.c > @@ -1466,6 +1466,7 @@ static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock) > raw_spin_lock_irqsave(&lock->wait_lock, flags); > } > > + trace_contended_release(lock); > /* > * The wakeup next waiter path does not suffer from the above > * race. See the comments there. > diff --git a/kernel/locking/rwbase_rt.c b/kernel/locking/rwbase_rt.c > index 82e078c0665a..74da5601018f 100644 > --- a/kernel/locking/rwbase_rt.c > +++ b/kernel/locking/rwbase_rt.c > @@ -174,6 +174,8 @@ static void __sched __rwbase_read_unlock(struct rwbase_rt *rwb, > static __always_inline void rwbase_read_unlock(struct rwbase_rt *rwb, > unsigned int state) > { > + if (trace_contended_release_enabled() && rt_mutex_owner(&rwb->rtmutex)) > + trace_contended_release(rwb); > /* > * rwb->readers can only hit 0 when a writer is waiting for the > * active readers to leave the critical section. > @@ -205,6 +207,8 @@ static inline void rwbase_write_unlock(struct rwbase_rt *rwb) > unsigned long flags; > > raw_spin_lock_irqsave(&rtm->wait_lock, flags); > + if (trace_contended_release_enabled() && rt_mutex_has_waiters(rtm)) > + trace_contended_release(rwb); > __rwbase_write_unlock(rwb, WRITER_BIAS, flags); > } > > @@ -214,6 +218,8 @@ static inline void rwbase_write_downgrade(struct rwbase_rt *rwb) > unsigned long flags; > > raw_spin_lock_irqsave(&rtm->wait_lock, flags); > + if (trace_contended_release_enabled() && rt_mutex_has_waiters(rtm)) > + trace_contended_release(rwb); > /* Release it and account current as reader */ > __rwbase_write_unlock(rwb, WRITER_BIAS - 1, flags); > } > diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c > index bf647097369c..602d5fd3c91a 100644 > --- a/kernel/locking/rwsem.c > +++ b/kernel/locking/rwsem.c > @@ -1387,6 +1387,8 @@ static inline void __up_read(struct rw_semaphore *sem) > rwsem_clear_reader_owned(sem); > tmp = atomic_long_add_return_release(-RWSEM_READER_BIAS, &sem->count); > DEBUG_RWSEMS_WARN_ON(tmp < 0, sem); > + if (trace_contended_release_enabled() && (tmp & RWSEM_FLAG_WAITERS)) > + trace_contended_release(sem); > if (unlikely((tmp & (RWSEM_LOCK_MASK|RWSEM_FLAG_WAITERS)) == > RWSEM_FLAG_WAITERS)) { > clear_nonspinnable(sem); > @@ -1413,8 +1415,10 @@ static inline void __up_write(struct rw_semaphore *sem) > preempt_disable(); > rwsem_clear_owner(sem); > tmp = atomic_long_fetch_add_release(-RWSEM_WRITER_LOCKED, &sem->count); > - if (unlikely(tmp & RWSEM_FLAG_WAITERS)) > + if (unlikely(tmp & RWSEM_FLAG_WAITERS)) { > + trace_contended_release(sem); > rwsem_wake(sem); > + } > preempt_enable(); > } > > @@ -1437,8 +1441,10 @@ static inline void __downgrade_write(struct rw_semaphore *sem) > tmp = atomic_long_fetch_add_release( > -RWSEM_WRITER_LOCKED+RWSEM_READER_BIAS, &sem->count); > rwsem_set_reader_owned(sem); > - if (tmp & RWSEM_FLAG_WAITERS) > + if (tmp & RWSEM_FLAG_WAITERS) { > + trace_contended_release(sem); > rwsem_downgrade_wake(sem); > + } > preempt_enable(); > } > > diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c > index 74d41433ba13..35ac3498dca5 100644 > --- a/kernel/locking/semaphore.c > +++ b/kernel/locking/semaphore.c > @@ -230,6 +230,10 @@ void __sched up(struct semaphore *sem) > sem->count++; > else > __up(sem, &wake_q); > + > + if (trace_contended_release_enabled() && !wake_q_empty(&wake_q)) > + trace_contended_release(sem); > + > raw_spin_unlock_irqrestore(&sem->lock, flags); > if (!wake_q_empty(&wake_q)) > wake_up_q(&wake_q); > -- > 2.52.0 >