linux-kernel - [tip: locking/core] locking/rwsem: Add __always_inline annotation to __down_write

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Message-ID: <172052528498.2215.9206229756576396995.tip-bot2@tip-bot2>
Date: Tue, 09 Jul 2024 11:41:24 -0000
From: "tip-bot2 for John Stultz" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Tim Murray <timmurray@...gle.com>, John Stultz <jstultz@...gle.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>,
 Waiman Long <longman@...hat.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: locking/core] locking/rwsem: Add __always_inline annotation to
 __down_write_common() and inlined callers

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     e81859fe64ad42dccefe134d1696e0635f78d763
Gitweb:        https://git.kernel.org/tip/e81859fe64ad42dccefe134d1696e0635f78d763
Author:        John Stultz <jstultz@...gle.com>
AuthorDate:    Mon, 08 Jul 2024 23:08:27 -07:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 09 Jul 2024 13:26:26 +02:00

locking/rwsem: Add __always_inline annotation to __down_write_common() and inlined callers

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

So add __always_inline annotation to the common function (as
well as the inlined helper callers) to force it to be inlined
so a more useful blocking function will be listed (via wchan).

This mirrors commit 92cc5d00a431 ("locking/rwsem: Add
__always_inline annotation to __down_read_common() and inlined
callers") which did the same for __down_read_common.

I sort of worry that I'm playing wack-a-mole here, and talking
with compiler people, they tell me inline means nothing, which
makes me want to cry a little. So I'm wondering if we need to
replace all the inlines with __always_inline, or remove them
because either we mean something by it, or not.

Fixes: c995e638ccbb ("locking/rwsem: Fold __down_{read,write}*()")
Reported-by: Tim Murray <timmurray@...gle.com>
Signed-off-by: John Stultz <jstultz@...gle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Waiman Long <longman@...hat.com>
Link: https://lkml.kernel.org/r/20240709060831.495366-1-jstultz@google.com
---
 kernel/locking/rwsem.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
index c6d17ae..33cac79 100644
--- a/kernel/locking/rwsem.c
+++ b/kernel/locking/rwsem.c
@@ -1297,7 +1297,7 @@ static inline int __down_read_trylock(struct rw_semaphore *sem)
 /*
  * lock for writing
  */
-static inline int __down_write_common(struct rw_semaphore *sem, int state)
+static __always_inline int __down_write_common(struct rw_semaphore *sem, int state)
 {
 	int ret = 0;
 
@@ -1310,12 +1310,12 @@ static inline int __down_write_common(struct rw_semaphore *sem, int state)
 	return ret;
 }
 
-static inline void __down_write(struct rw_semaphore *sem)
+static __always_inline void __down_write(struct rw_semaphore *sem)
 {
 	__down_write_common(sem, TASK_UNINTERRUPTIBLE);
 }
 
-static inline int __down_write_killable(struct rw_semaphore *sem)
+static __always_inline int __down_write_killable(struct rw_semaphore *sem)
 {
 	return __down_write_common(sem, TASK_KILLABLE);
 }