Re: [PATCH v2] locking/ww_mutex: Initialize waiter.ww_ctx properly

From: Guenter Roeck <linux@roeck-us.net>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@kernel.org>,
	Juri Lelli <juri.lelli@redhat.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	Will Deacon <will@kernel.org>, Waiman Long <longman@redhat.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Mike Galbraith <efault@gmx.de>
Subject: Re: [PATCH v2] locking/ww_mutex: Initialize waiter.ww_ctx properly
Date: Thu, 19 Aug 2021 21:40:15 -0700	[thread overview]
Message-ID: <20210820044015.GA2751666@roeck-us.net> (raw)

On Thu, Aug 19, 2021 at 09:30:30PM +0200, Sebastian Andrzej Siewior wrote:
> 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@roeck-us.net>
> Suggested-by: Peter Zijlstra <peterz@infradead.org>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Tested-by: Guenter Roeck <linux@roeck-us.net>

> ---
> 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
>