linux-kernel - Re: [PATCH v5 3/4] drm/vc4: Check for the binner bo before handling OOM interrupt

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Message-ID: <87v9zf806m.fsf@anholt.net>
Date:   Mon, 15 Apr 2019 13:48:17 -0700
From:   Eric Anholt <eric@...olt.net>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Eben Upton <eben@...pberrypi.org>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Subject: Re: [PATCH v5 3/4] drm/vc4: Check for the binner bo before handling OOM interrupt

Paul Kocialkowski <paul.kocialkowski@...tlin.com> writes:

> Since the OOM interrupt directly deals with the binner bo, it doesn't
> make sense to try and handle it without a binner buffer registered.
>
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> ---
>  drivers/gpu/drm/vc4/vc4_irq.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_irq.c b/drivers/gpu/drm/vc4/vc4_irq.c
> index ffd0a4388752..723dc86b4511 100644
> --- a/drivers/gpu/drm/vc4/vc4_irq.c
> +++ b/drivers/gpu/drm/vc4/vc4_irq.c
> @@ -64,6 +64,9 @@ vc4_overflow_mem_work(struct work_struct *work)
>  	struct vc4_exec_info *exec;
>  	unsigned long irqflags;
>  
> +	if (!bo)
> +		return;
> +
>  	bin_bo_slot = vc4_v3d_get_bin_slot(vc4);
>  	if (bin_bo_slot < 0) {
>  		DRM_ERROR("Couldn't allocate binner overflow mem\n");
> -- 
> 2.21.0

I don't think this is going to be race-free.  You're checking outside of
a lock, then proceeding to use it even if (in patch 4) the bin BO was in
the process of being freed during the file close path.  Can we put all
of the overflow process here under the same lock as freeing?

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