linux-kernel - Re: [PATCH 2/3] drm/msm: Fix races managing the OOB state for timestamp vs timestamps.

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Message-ID: <CAF6AEGuXeU18cUKGogtJD7O4SPUgFVQZcw3H-MDXNR5HAXcgFw@mail.gmail.com>
Date:   Thu, 28 Jan 2021 12:40:52 -0800
From:   Rob Clark <robdclark@...il.com>
To:     Eric Anholt <eric@...olt.net>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Sean Paul <sean@...rly.run>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH 2/3] drm/msm: Fix races managing the OOB state for
 timestamp vs timestamps.

On Wed, Jan 27, 2021 at 3:39 PM Eric Anholt <eric@...olt.net> wrote:
>
> Now that we're not racing with GPU setup, also fix races of timestamps
> against other timestamps.  In CI, we were seeing this path trigger
> timeouts on setting the GMU bit, especially on the first set of tests
> right after boot (it's probably easier to lose the race than one might
> think, given that we start many tests in parallel, and waiting for NFS
> to page in code probably means that lots of tests hit the same point
> of screen init at the same time).

Could you add the error msg to the commit msg, to make it more easily
searchable?

BR,
-R

> Signed-off-by: Eric Anholt <eric@...olt.net>
> Cc: stable@...r.kernel.org # v5.9
> ---
>  drivers/gpu/drm/msm/adreno/a6xx_gpu.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> index 7424a70b9d35..e8f0b5325a7f 100644
> --- a/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a6xx_gpu.c
> @@ -1175,6 +1175,9 @@ static int a6xx_get_timestamp(struct msm_gpu *gpu, uint64_t *value)
>  {
>         struct adreno_gpu *adreno_gpu = to_adreno_gpu(gpu);
>         struct a6xx_gpu *a6xx_gpu = to_a6xx_gpu(adreno_gpu);
> +       static DEFINE_MUTEX(perfcounter_oob);
> +
> +       mutex_lock(&perfcounter_oob);
>
>         /* Force the GPU power on so we can read this register */
>         a6xx_gmu_set_oob(&a6xx_gpu->gmu, GMU_OOB_PERFCOUNTER_SET);
> @@ -1183,6 +1186,7 @@ static int a6xx_get_timestamp(struct msm_gpu *gpu, uint64_t *value)
>                 REG_A6XX_RBBM_PERFCTR_CP_0_HI);
>
>         a6xx_gmu_clear_oob(&a6xx_gpu->gmu, GMU_OOB_PERFCOUNTER_SET);
> +       mutex_unlock(&perfcounter_oob);
>         return 0;
>  }
>
> --
> 2.30.0
>