linux-kernel - Re: [PATCH -rt] rtmutex: enable deadlock detection in the ww_mutex

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Date:	Tue, 27 Jan 2015 07:49:24 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Gustavo Bittencourt <gbitten@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH -rt] rtmutex: enable deadlock detection in the
 ww_mutex_lock functions

You should probably CC -rt maintainers when submitting a -rt patch.

On Tue, 2015-01-27 at 03:53 -0200, Gustavo Bittencourt wrote: 
> According the ww-mutex-design.txt documentation,  the ww_mutex_lock_interruptible and ww_mutex_lock functions should return -EDEADLK when faced with a deadlock. To do so, the flag detect_deadlock in the rt_mutex_slowlock calls should be enabled. This patch corrects potential deadlocks when running PREEMPT_RT with nouveau driver.
> 
> Kernel v3.14-rt
> 
> Signed-off-by: Gustavo Bittencourt<gbitten@...il.com>
> ---
>   kernel/locking/rtmutex.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
> index 6c40660..3f6ef91 100644
> --- a/kernel/locking/rtmutex.c
> +++ b/kernel/locking/rtmutex.c
> @@ -1965,7 +1965,7 @@ __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ww_c
>   	might_sleep();
>   
>   	mutex_acquire(&lock->base.dep_map, 0, 0,_RET_IP_);
> -	ret = rt_mutex_slowlock(&lock->base.lock, TASK_INTERRUPTIBLE, NULL, 0, ww_ctx);
> +	ret = rt_mutex_slowlock(&lock->base.lock, TASK_INTERRUPTIBLE, NULL, 1, ww_ctx);
>   	if (ret)
>   		mutex_release(&lock->base.dep_map, 1,_RET_IP_);
>   	else if (!ret && ww_ctx->acquired > 1)
> @@ -1984,7 +1984,7 @@ __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ww_ctx)
>   
>   	mutex_acquire_nest(&lock->base.dep_map, 0, 0, &ww_ctx->dep_map,
>   			_RET_IP_);
> -	ret = rt_mutex_slowlock(&lock->base.lock, TASK_UNINTERRUPTIBLE, NULL, 0, ww_ctx);
> +	ret = rt_mutex_slowlock(&lock->base.lock, TASK_UNINTERRUPTIBLE, NULL, 1, ww_ctx);
>   	if (ret)
>   		mutex_release(&lock->base.dep_map, 1,_RET_IP_);
>   	else if (!ret && ww_ctx->acquired > 1)
> -- 1.9.1
> 
> --
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