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

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Message-ID: <21a944a054790c0a5b542183b7d5fa54483232be.camel@mailbox.org>
Date: Mon, 24 Feb 2025 10:57:26 +0100
From: Philipp Stanner <phasta@...lbox.org>
To: phasta@...nel.org, qianyi liu <liuqianyi125@...il.com>, Danilo Krummrich
 <dakr@...nel.org>, Matthew Brost <matthew.brost@...el.com>, 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
Subject: Re: [PATCH] drm/scheduler: Fix mem leak when last_scheduled signaled

On Mon, 2025-02-24 at 10:52 +0100, Philipp Stanner wrote:
> Hello,
> 
> subject line: please write "drm/sched" instead of "drm/scheduler". It
> has become the norm
> 
> On Fri, 2025-02-21 at 14:27 +0800, qianyi liu wrote:
> > Problem: If prev(last_scheduled) was already signaled I encountred
> > a
> 
> prev(last_scheduled) almost reads like a function call. Maybe write
> "prev / last_scheduled"?
> 
> > memory leak in drm_sched_entity_fini. This is because the
> > prev(last_scheduled) fence is not free properly.
> 
> s/free/freed
> 
> > 
> > Fix: Balance the prev(last_scheduled) fence refcnt when
> > dma_fence_add_callback failed.
> > 
> > Signed-off-by: qianyi liu <liuqianyi125@...il.com>
> > ---
> >  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);
> 
> But now the fence will also be put when prev == NULL. Is that
> intentional? It doesn't seem correct to me from looking at the commit
> message, which states "Balance […] refcnt when dma_fence_add_callback
> failed"
> 
> It didn't get clear to me immediately which dma_fence_get() your new
> dma_fence_put() balances. Can you ellaborate on that or maybe write a
> comment?
> 
> But also be handy of could share the kmemleak trace.

Argh.

-> "It would also be handy if you could share the kmemleak trace"

I should drink less…

P.


> 
> 
> Thanks
> P.
> 
> >  			drm_sched_entity_kill_jobs_cb(NULL, &job-
> > > finish_cb);
> > +		}
> >  
> >  		prev = &s_fence->finished;
> >  	}
>