linux-kernel - Re: [PATCH V3] drm/sched: Fix fence reference count leak

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Message-ID: <a5f389b1c08847fb658f4120b205521e4a8ea0c1.camel@mailbox.org>
Date: Mon, 10 Mar 2025 10:13:45 +0100
From: Philipp Stanner <phasta@...lbox.org>
To: Qianyi Liu <liuqianyi125@...il.com>, Danilo Krummrich <dakr@...nel.org>,
  Matthew Brost <matthew.brost@...el.com>, Philipp Stanner
 <phasta@...nel.org>, Christian König
 <ckoenig.leichtzumerken@...il.com>, Maarten Lankhorst
 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
 Daniel Vetter <daniel@...ll.ch>
Cc: dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org
Subject: Re: [PATCH V3] drm/sched: Fix fence reference count leak

Sorry for the delay

On Wed, 2025-02-26 at 17:05 +0800, Qianyi Liu wrote:
> From: qianyi liu <liuqianyi125@...il.com>
> 
> The last_scheduled fence leaked when an entity was being killed and
> adding its callback failed.

s/leaked/leaks

s/was being/is being

s/its callback/the cleanup callback

s/failed/fails


> 
> Decrement the reference count of prev when dma_fence_add_callback()
> fails, ensuring proper balance.
> 
> Cc: stable@...r.kernel.org
> Fixes: 2fdb8a8f07c2 ("drm/scheduler: rework entity flush, kill and
> fini")
> Signed-off-by: qianyi liu <liuqianyi125@...il.com>
> ---
> v2 -> v3: Rework commit message (Markus)
> v1 -> v2: Added 'Fixes:' tag and clarified commit message (Philipp
> and Matthew)
> ---
>  drivers/gpu/drm/scheduler/sched_entity.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c
> b/drivers/gpu/drm/scheduler/sched_entity.c
> index 69bcf0e99d57..1c0c14bcf726 100644
> --- a/drivers/gpu/drm/scheduler/sched_entity.c
> +++ b/drivers/gpu/drm/scheduler/sched_entity.c
> @@ -259,9 +259,12 @@ static void drm_sched_entity_kill(struct
> drm_sched_entity *entity)
>  		struct drm_sched_fence *s_fence = job->s_fence;
>  
>  		dma_fence_get(&s_fence->finished);
> -		if (!prev || dma_fence_add_callback(prev, &job-
> >finish_cb,
> -					  
> drm_sched_entity_kill_jobs_cb))
> +		if (!prev ||
> +		    dma_fence_add_callback(prev, &job->finish_cb,
> +					  
> drm_sched_entity_kill_jobs_cb)) {
> +			dma_fence_put(prev);

Please add a little comment about the dma_fence_put()'s purpose. Sth
like "Adding callback above failed. dma_fence_put() checks for NULL."

Then we should be good I think

Thx

>  			drm_sched_entity_kill_jobs_cb(NULL, &job-
> >finish_cb);
> +		}



}


>  
>  		prev = &s_fence->finished;
>  	}