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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: References: <20260331103451.1070175-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260331103451.1070175-1-usama.arif@linux.dev> X-Rspamd-Queue-Id: E0E332000B X-Stat-Signature: fko79ik5gtrh3kqyp1jy7ibnxy7ohoap X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1774959408-950269 X-HE-Meta: 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 nagPGTZj PpxQZ6dSOUVs45yQRlHVs1ehQUHYzN0LRxtPFi9NMCpG5Pxl8caYJe+GAFGCFPOrSN5EkgI+34atMvWtfHxfQ1jvkOiuBlFXMEHj/E0+3m8LB7fjX7OdhaFJL5H+cC/XuShw8L8xIcYRlIT7K58iLOob0aXWhGlsPvkvHRuOs7j8W3KmyMWnv5/SEKK186vYRflaf23OyiqACMOMy43An8stXdwusO3/mYi0OdmkLowJaLPdOQUBNUxv3PnWIg/lyyKh9UPNXla5fCdVocE5cPEIzfi+KFioBYbtq7JkGweL4Mj8qdA/8C1iSkTwMA1TEOZaAxU8PVD2n1bYrCJF/sbRUxA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Mar 31, 2026 at 03:34:50AM -0700, Usama Arif wrote: > On Thu, 26 Mar 2026 15:10:02 +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 > > --- > > 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); > > + > > This won't compile? waiter is declared in the if block, so you are using > it outside scope here. > Thanks for the feedback, Usama. waiter is declared at function scope, right on top. It's also assigned before the if block, so it's still in scope at the tracepoint.