linux-kernel - Re: [PATCH v1 1/6] drm/lima: fix devfreq refcount imbalance for job timeouts

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Date: Thu, 18 Jan 2024 09:36:34 +0800
From: Qiang Yu <yuq825@...il.com>
To: Erico Nunes <nunes.erico@...il.com>
Cc: dri-devel@...ts.freedesktop.org, lima@...ts.freedesktop.org, 
	anarsoul@...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>, 
	Sumit Semwal <sumit.semwal@...aro.org>, christian.koenig@....com, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 1/6] drm/lima: fix devfreq refcount imbalance for job timeouts

So this is caused by same job trigger both done and timeout handling?
I think a better way to solve this is to make sure only one handler
(done or timeout) process the job instead of just making lima_pm_idle()
unique.

Regards,
Qiang

On Wed, Jan 17, 2024 at 11:12 AM Erico Nunes <nunes.erico@...il.com> wrote:
>
> In case a task manages to complete but it took just long enough to also
> trigger the timeout handler, the current code results in a refcount
> imbalance on lima_pm_idle.
>
> While this can be a rare occurrence, when it happens it may fill user
> logs with stack traces such as:
>
> [10136.669170] WARNING: CPU: 0 PID: 0 at drivers/gpu/drm/lima/lima_devfreq.c:205 lima_devfreq_record_idle+0xa0/0xb0
> ...
> [10136.669459] pc : lima_devfreq_record_idle+0xa0/0xb0
> ...
> [10136.669628] Call trace:
> [10136.669634]  lima_devfreq_record_idle+0xa0/0xb0
> [10136.669646]  lima_sched_pipe_task_done+0x5c/0xb0
> [10136.669656]  lima_gp_irq_handler+0xa8/0x120
> [10136.669666]  __handle_irq_event_percpu+0x48/0x160
> [10136.669679]  handle_irq_event+0x4c/0xc0
>
> The imbalance happens because lima_sched_pipe_task_done() already calls
> lima_pm_idle for this case if there was no error.
> Check the error flag in the timeout handler to ensure we can never run
> into this case.
>
> Signed-off-by: Erico Nunes <nunes.erico@...il.com>
> ---
>  drivers/gpu/drm/lima/lima_sched.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/lima/lima_sched.c b/drivers/gpu/drm/lima/lima_sched.c
> index c3bf8cda8498..66317296d831 100644
> --- a/drivers/gpu/drm/lima/lima_sched.c
> +++ b/drivers/gpu/drm/lima/lima_sched.c
> @@ -427,7 +427,8 @@ static enum drm_gpu_sched_stat lima_sched_timedout_job(struct drm_sched_job *job
>         pipe->current_vm = NULL;
>         pipe->current_task = NULL;
>
> -       lima_pm_idle(ldev);
> +       if (pipe->error)
> +               lima_pm_idle(ldev);
>
>         drm_sched_resubmit_jobs(&pipe->base);
>         drm_sched_start(&pipe->base, true);
> --
> 2.43.0
>