On Fri, Oct 23, 2015 at 09:42:27AM +0100, Tvrtko Ursulin wrote:
>
> On 19/10/15 16:32, Tomas Elf wrote:
> >Grab execlist lock when cleaning up execlist queues after GPU reset to avoid
> >concurrency problems between the context event interrupt handler and the reset
> >path immediately following a GPU reset.
> >
> >* v2 (Chris Wilson):
> >Do execlist check and use simpler form of spinlock functions.
> >
> >Signed-off-by: Tomas Elf <tomas.elf@xxxxxxxxx>
> >---
> > drivers/gpu/drm/i915/i915_gem.c | 23 ++++++++++++++---------
> > 1 file changed, 14 insertions(+), 9 deletions(-)
> >
> >diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> >index e57061a..2c7a0b7 100644
> >--- a/drivers/gpu/drm/i915/i915_gem.c
> >+++ b/drivers/gpu/drm/i915/i915_gem.c
> >@@ -2753,18 +2753,23 @@ static void i915_gem_reset_ring_cleanup(struct drm_i915_private *dev_priv,
> > * are the ones that keep the context and ringbuffer backing objects
> > * pinned in place.
> > */
> >- while (!list_empty(&ring->execlist_queue)) {
> >- struct drm_i915_gem_request *submit_req;
> >
> >- submit_req = list_first_entry(&ring->execlist_queue,
> >- struct drm_i915_gem_request,
> >- execlist_link);
> >- list_del(&submit_req->execlist_link);
> >+ if (i915.enable_execlists) {
> >+ spin_lock_irq(&ring->execlist_lock);
> >+ while (!list_empty(&ring->execlist_queue)) {
> >+ struct drm_i915_gem_request *submit_req;
> >
> >- if (submit_req->ctx != ring->default_context)
> >- intel_lr_context_unpin(submit_req);
> >+ submit_req = list_first_entry(&ring->execlist_queue,
> >+ struct drm_i915_gem_request,
> >+ execlist_link);
> >+ list_del(&submit_req->execlist_link);
> >
> >- i915_gem_request_unreference(submit_req);
> >+ if (submit_req->ctx != ring->default_context)
> >+ intel_lr_context_unpin(submit_req);
> >+
> >+ i915_gem_request_unreference(submit_req);
> >+ }
> >+ spin_unlock_irq(&ring->execlist_lock);
>
> Can't this, in theory at least, end up calling drm_gem_object_unreference in
> a couple of code paths, which can sleep, while holding a spinlock?
>
> If this cannot happen in practice for some reason it would probably be good
> to put a comment explaining it.
>
> Or I am missing something?
It can indeed I think. Tvrtko, since I'm off to KS next week and you have
push access, can you pls push the revert if this checks out?
Thanks, Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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