linux-kernel - Re: [PATCH v1] drm/scheduler: Don't kill jobs in interrupt context

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Message-ID: <7f0d7ade-1d59-2c43-c1b2-1fa847eb741a@collabora.com>
Date:   Wed, 13 Apr 2022 09:05:46 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Erico Nunes <nunes.erico@...il.com>,
        Andrey Grodzovsky <andrey.grodzovsky@....com>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Steven Price <steven.price@....com>,
        Rob Herring <robh@...nel.org>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        Rob Clark <robdclark@...il.com>,
        Dmitry Osipenko <digetx@...il.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Qiang Yu <yuq825@...il.com>
Subject: Re: [PATCH v1] drm/scheduler: Don't kill jobs in interrupt context

On 4/13/22 01:59, Erico Nunes wrote:
> On Tue, Apr 12, 2022 at 9:41 PM Andrey Grodzovsky
> <andrey.grodzovsky@....com> wrote:
>>
>>
>> On 2022-04-12 14:20, Dmitry Osipenko wrote:
>>> On 4/12/22 19:51, Andrey Grodzovsky wrote:
>>>> On 2022-04-11 18:15, Dmitry Osipenko wrote:
>>>>> Interrupt context can't sleep. Drivers like Panfrost and MSM are taking
>>>>> mutex when job is released, and thus, that code can sleep. This results
>>>>> into "BUG: scheduling while atomic" if locks are contented while job is
>>>>> freed. There is no good reason for releasing scheduler's jobs in IRQ
>>>>> context, hence use normal context to fix the trouble.
>>>>
>>>> I am not sure this is the beast Idea to leave job's sw fence signalling
>>>> to be
>>>> executed in system_wq context which is prone to delays of executing
>>>> various work items from around the system. Seems better to me to leave the
>>>> fence signaling within the IRQ context and offload only the job freeing or,
>>>> maybe handle rescheduling to thread context within drivers implemention
>>>> of .free_job cb. Not really sure which is the better.
>>> We're talking here about killing jobs when driver destroys context,
>>> which doesn't feel like it needs to be a fast path. I could move the
>>> signalling into drm_sched_entity_kill_jobs_cb() and use unbound wq, but
>>> do we really need this for a slow path?
>>
>>
>> You can't move the signaling back to drm_sched_entity_kill_jobs_cb
>> since this will bring back the lockdep splat that 'drm/sched: Avoid
>> lockdep spalt on killing a processes'
>> was fixing.
>>
>> I see your point and i guess we can go this way too. Another way would
>> be to add to
>> panfrost and msm job a  work_item and reschedule to thread context from
>> within their
>> .free_job callbacks but that probably to cumbersome to be justified here.
> 
> FWIW since this mentioned individual drivers, commit 'drm/sched: Avoid
> lockdep spalt on killing a processes' also introduced problems for
> lima.
> There were some occurrences in our CI
> https://gitlab.freedesktop.org/mesa/mesa/-/jobs/20980982/raw .
> Later I found it also reproducible on normal usage when just closing
> applications, so it may be affecting users too.
> 
> I tested this patch and looks like it fixes things for lima.

This patch indeed should fix that lima bug. Feel free to give yours
tested-by :)