linux-kernel - Re: [PATCH] drm/scheduler: Fix mem leak when last

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Message-ID: <0bb7b9c428bdefe36afb43272c73da7e04a001ed.camel@mailbox.org>
Date: Tue, 25 Feb 2025 08:23:56 +0100
From: Philipp Stanner <phasta@...lbox.org>
To: Qianyi Liu <liuqianyi125@...il.com>
Cc: airlied@...il.com, ckoenig.leichtzumerken@...il.com, dakr@...nel.org, 
 daniel@...ll.ch, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org,  maarten.lankhorst@...ux.intel.com,
 matthew.brost@...el.com, mripard@...nel.org,  phasta@...nel.org,
 tzimmermann@...e.de
Subject: Re: [PATCH] drm/scheduler: Fix mem leak when last_scheduled signaled

On Tue, 2025-02-25 at 11:12 +0800, Qianyi Liu wrote:
> Hello Philipp,
> 
> Thank you for your patient reply. Let's first clarify the issue and
> send a new
> patch if necessary.
> 
> As soon as it enters the drm_sched_entity_kill function, the entity
> ->last_scheduled reference count is incremented by 1. If there are
> still jobs in
> the current entity, it will enter the while loop, assuming there is
> only one job
> left. If entity->last_scheduled has already been signaled, it will
> enter
> drm_sched_entity_kill_jobs_cb, but because null is passed in, the
> last_scheduled reference count will not be correctly reduced by 1.
> 
> Because the prev pointer has been updated to &s_fence->finished, the
> dma_fence_put in the last line only reduces the reference count of
> s_fence->finished.
> The reference count of entity->last_scheduled was not reduced by
> 1, causing a memory leak.
> 
> We should subtract 1 from the reference count of the prev when
> dma_fence_add_callback
> fails, which is called balance.
> 
> Best Regards.
> QianYi.

OK, thanks for clarification.

I think, next to the other feedback, it would be good to have a brief
version of the above explanation in your commit message, since this
clearly describes the problem and the proposed solution.

Please address the feedback by Matt and myself in a v2.

(and btw., please don't remove the original e-mail content when
answering – that's uncommon on-list. Only when the threads are getting
huge one removes parts not addressed by the answer from the quoted
content ;)


Thanks
P.