Re: [PATCH] mutex: fix deadlock injection

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Jul 30, 2013 at 10:13:41AM +0200, Maarten Lankhorst wrote:
> The check needs to be for > 1, because ctx->acquired is already incremented.
> This will prevent ww_mutex_lock_slow from returning -EDEADLK and not locking
> the mutex. It caused a lot of false gpu lockups on radeon with
> CONFIG_DEBUG_WW_MUTEX_SLOWPATH=y because a function that shouldn't be able
> to return -EDEADLK did.
> 
> Cc: Alex Deucher <alexander.deucher@amd.com>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>

Oops, thanks for catching this.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
> diff --git a/kernel/mutex.c b/kernel/mutex.c
> index ff05f4b..a52ee7bb 100644
> --- a/kernel/mutex.c
> +++ b/kernel/mutex.c
> @@ -686,7 +686,7 @@ __ww_mutex_lock(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
>  	might_sleep();
>  	ret =  __mutex_lock_common(&lock->base, TASK_UNINTERRUPTIBLE,
>  				   0, &ctx->dep_map, _RET_IP_, ctx);
> -	if (!ret && ctx->acquired > 0)
> +	if (!ret && ctx->acquired > 1)
>  		return ww_mutex_deadlock_injection(lock, ctx);
>  
>  	return ret;
> @@ -702,7 +702,7 @@ __ww_mutex_lock_interruptible(struct ww_mutex *lock, struct ww_acquire_ctx *ctx)
>  	ret = __mutex_lock_common(&lock->base, TASK_INTERRUPTIBLE,
>  				  0, &ctx->dep_map, _RET_IP_, ctx);
>  
> -	if (!ret && ctx->acquired > 0)
> +	if (!ret && ctx->acquired > 1)
>  		return ww_mutex_deadlock_injection(lock, ctx);
>  
>  	return ret;
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch