Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> If the request->wa_tail is 0 (because it landed exactly on the end of
> the ringbuffer), when we reconstruct request->tail following a reset we
> fill in an illegal value (-8 or 0x001ffff8). As a result, RING_HEAD is
> never able to catch up with RING_TAIL and the GPU spins endlessly. If
> the ring contains a couple of breadcrumbs, even our hangcheck is unable
> to catch the busy-looping as the ACTHD and seqno continually advance.
>
> v2: Move the wrap into a common intel_ring_wrap().
>
> Fixes: a3aabe86a340 ("drm/i915/execlists: Reinitialise context image after GPU hang")
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.10+
Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_lrc.c | 4 +++-
> drivers/gpu/drm/i915/intel_ringbuffer.h | 10 ++++++++--
> 2 files changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index b75df70e8e0e..32fb8ad3fd36 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -1278,7 +1278,9 @@ static void reset_common_ring(struct intel_engine_cs *engine,
> GEM_BUG_ON(request->ctx != port[0].request->ctx);
>
> /* Reset WaIdleLiteRestore:bdw,skl as well */
> - request->tail = request->wa_tail - WA_TAIL_DWORDS * sizeof(u32);
> + request->tail =
> + intel_ring_wrap(request->ring,
> + request->wa_tail - WA_TAIL_DWORDS*sizeof(u32));
> GEM_BUG_ON(!IS_ALIGNED(request->tail, 8));
> }
>
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index 166aa1ae65cf..17ac44980d84 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -515,12 +515,18 @@ intel_ring_advance(struct drm_i915_gem_request *req, u32 *cs)
> }
>
> static inline u32
> -intel_ring_offset(struct drm_i915_gem_request *req, void *addr)
> +intel_ring_wrap(const struct intel_ring *ring, u32 pos)
> +{
> + return pos & (ring->size - 1);
> +}
> +
> +static inline u32
> +intel_ring_offset(const struct drm_i915_gem_request *req, void *addr)
> {
> /* Don't write ring->size (equivalent to 0) as that hangs some GPUs. */
> u32 offset = addr - req->ring->vaddr;
> GEM_BUG_ON(offset > req->ring->size);
> - return offset & (req->ring->size - 1);
> + return intel_ring_wrap(req->ring, offset);
> }
>
> void intel_ring_update_space(struct intel_ring *ring);
> --
> 2.11.0
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