Chris Wilson <ch...@chris-wilson.co.uk> writes:
> If a semaphore is waiting on another ring, which in turn happens to be
> waiting on the first ring, but that second semaphore has been signalled,
> we will be able to kick the second ring and so can treat the first ring
> as a valid WAIT and not as HUNG.
>
> v2: Be paranoid and cap the potential recursion depth whilst visiting
> the semaphore signallers. (Mika)
>
> References: https://bugs.freedesktop.org/show_bug.cgi?id=54226
> References: https://bugs.freedesktop.org/show_bug.cgi?id=75502
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuopp...@linux.intel.com>
> Cc: sta...@vger.kernel.org
> ---
Reviewed-by: Mika Kuoppala <mika.kuopp...@intel.com>
> drivers/gpu/drm/i915/i915_irq.c | 18 ++++++++++++++----
> drivers/gpu/drm/i915/intel_ringbuffer.h | 2 +-
> 2 files changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index a702303eab08..2974698f8f27 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -2831,10 +2831,14 @@ static int semaphore_passed(struct intel_engine_cs
> *ring)
> struct intel_engine_cs *signaller;
> u32 seqno, ctl;
>
> - ring->hangcheck.deadlock = true;
> + ring->hangcheck.deadlock++;
>
> signaller = semaphore_waits_for(ring, &seqno);
> - if (signaller == NULL || signaller->hangcheck.deadlock)
> + if (signaller == NULL)
> + return -1;
> +
> + /* Prevent pathological recursion due to driver bugs */
> + if (signaller->hangcheck.deadlock >= I915_NUM_RINGS)
> return -1;
>
> /* cursory check for an unkickable deadlock */
> @@ -2842,7 +2846,13 @@ static int semaphore_passed(struct intel_engine_cs
> *ring)
> if (ctl & RING_WAIT_SEMAPHORE && semaphore_passed(signaller) < 0)
> return -1;
>
> - return i915_seqno_passed(signaller->get_seqno(signaller, false), seqno);
> + if (i915_seqno_passed(signaller->get_seqno(signaller, false), seqno))
> + return 1;
> +
> + if (signaller->hangcheck.deadlock)
> + return -1;
> +
> + return 0;
> }
>
> static void semaphore_clear_deadlocks(struct drm_i915_private *dev_priv)
> @@ -2851,7 +2861,7 @@ static void semaphore_clear_deadlocks(struct
> drm_i915_private *dev_priv)
> int i;
>
> for_each_ring(ring, dev_priv, i)
> - ring->hangcheck.deadlock = false;
> + ring->hangcheck.deadlock = 0;
> }
>
> static enum intel_ring_hangcheck_action
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h
> b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index 24357c597b54..31c2aab8ad2c 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -55,7 +55,7 @@ struct intel_ring_hangcheck {
> u32 seqno;
> int score;
> enum intel_ring_hangcheck_action action;
> - bool deadlock;
> + int deadlock;
> };
>
> struct intel_ringbuffer {
> --
> 2.0.0
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