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    Subject[PATCH 5.3 126/197] drm/panfrost: Handle resetting on timeout better
    Date
    From: Steven Price <steven.price@arm.com>

    commit 5b3ec8134f5f9fa1ed0a538441a495521078bbee upstream.

    Panfrost uses multiple schedulers (one for each slot, so 2 in reality),
    and on a timeout has to stop all the schedulers to safely perform a
    reset. However more than one scheduler can trigger a timeout at the same
    time. This race condition results in jobs being freed while they are
    still in use.

    When stopping other slots use cancel_delayed_work_sync() to ensure that
    any timeout started for that slot has completed. Also use
    mutex_trylock() to obtain reset_lock. This means that only one thread
    attempts the reset, the other threads will simply complete without doing
    anything (the first thread will wait for this in the call to
    cancel_delayed_work_sync()).

    While we're here and since the function is already dependent on
    sched_job not being NULL, let's remove the unnecessary checks.

    Fixes: aa20236784ab ("drm/panfrost: Prevent concurrent resets")
    Tested-by: Neil Armstrong <narmstrong@baylibre.com>
    Signed-off-by: Steven Price <steven.price@arm.com>
    Cc: stable@vger.kernel.org
    Signed-off-by: Rob Herring <robh@kernel.org>
    Link: https://patchwork.freedesktop.org/patch/msgid/20191009094456.9704-1-steven.price@arm.com
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/gpu/drm/panfrost/panfrost_job.c | 16 +++++++++++-----
    1 file changed, 11 insertions(+), 5 deletions(-)

    --- a/drivers/gpu/drm/panfrost/panfrost_job.c
    +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
    @@ -384,13 +384,19 @@ static void panfrost_job_timedout(struct
    job_read(pfdev, JS_TAIL_LO(js)),
    sched_job);

    - mutex_lock(&pfdev->reset_lock);
    + if (!mutex_trylock(&pfdev->reset_lock))
    + return;

    - for (i = 0; i < NUM_JOB_SLOTS; i++)
    - drm_sched_stop(&pfdev->js->queue[i].sched, sched_job);
    + for (i = 0; i < NUM_JOB_SLOTS; i++) {
    + struct drm_gpu_scheduler *sched = &pfdev->js->queue[i].sched;

    - if (sched_job)
    - drm_sched_increase_karma(sched_job);
    + drm_sched_stop(sched, sched_job);
    + if (js != i)
    + /* Ensure any timeouts on other slots have finished */
    + cancel_delayed_work_sync(&sched->work_tdr);
    + }
    +
    + drm_sched_increase_karma(sched_job);

    /* panfrost_core_dump(pfdev); */


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