linux-kernel - [PATCH v2] locking/ww_mutex: Initialize waiter.ww

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Date:   Thu, 19 Aug 2021 21:30:30 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Mike Galbraith <efault@....de>,
        Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH v2] locking/ww_mutex: Initialize waiter.ww_ctx properly

The gathering of the debug code for the ww-mutex initialized moved the
POISON initialiation into one spot and only set waiter.ww_ctx if the
ww_ctx was non-NULL thus keeping the POISON value in ww-mutex case.

For ww-mutex without a context it is expected to set the context to
NULL, the poison value was intended only for the regular mutex.

Always initialized waiter.ww_ctx to ww_ctx in the ww-mutex case.

Fixes: c0afb0ffc06e6 ("locking/ww_mutex: Gather mutex_waiter initialization")
Reported-by: Guenter Roeck <linux@...ck-us.net>
Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
v1…v2: Use PeterZ' approach.

 kernel/locking/mutex.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index 05b68931622d1..2c70213934cd4 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -614,7 +614,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 
 	debug_mutex_lock_common(lock, &waiter);
 	waiter.task = current;
-	if (ww_ctx)
+	if (use_ww_ctx)
 		waiter.ww_ctx = ww_ctx;
 
 	lock_contended(&lock->dep_map, ip);
-- 
2.33.0