linux-kernel - [PATCH v2] locking/rwsem: Add __always_inline annotation to __down_read

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Message-ID: <20230412035905.3184199-1-jstultz@google.com>
Date:   Wed, 12 Apr 2023 03:59:05 +0000
From:   John Stultz <jstultz@...gle.com>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     John Stultz <jstultz@...gle.com>, Minchan Kim <minchan@...nel.org>,
        Tim Murray <timmurray@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>, kernel-team@...roid.com,
        stable@...r.kernel.org
Subject: [PATCH v2] locking/rwsem: Add __always_inline annotation to __down_read_common()

Apparently despite it being marked inline, the compiler
may not inline __down_read_common() which makes it difficult
to identify the cause of lock contention, as the blocked
function will always be listed as __down_read_common().

So this patch adds __always_inline annotation to the
function to force it to be inlines so the calling function
will be listed.

Cc: Minchan Kim <minchan@...nel.org>
Cc: Tim Murray <timmurray@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Will Deacon <will@...nel.org>
Cc: Waiman Long <longman@...hat.com>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: kernel-team@...roid.com
Cc: stable@...r.kernel.org
Fixes: c995e638ccbb ("locking/rwsem: Fold __down_{read,write}*()")
Reported-by: Tim Murray <timmurray@...gle.com>
Signed-off-by: John Stultz <jstultz@...gle.com>
---
v2: Reworked to use __always_inline instead of __sched as
    suggested by Waiman Long
---
 kernel/locking/rwsem.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index acb5a50309a1..e99eef8ea552 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -1240,7 +1240,7 @@ static struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem)
 /*
  * lock for reading
  */
-static inline int __down_read_common(struct rw_semaphore *sem, int state)
+static __always_inline int __down_read_common(struct rw_semaphore *sem, int state)
 {
 	int ret = 0;
 	long count;
-- 
2.40.0.577.gac1e443424-goog