Hi, On 15/11/15 13:32, Chris Wilson wrote: > The busywait in __i915_spin_request() does not respect pending signals > and so may consume the entire timeslice for the task instead of > returning to userspace to handle the signal.
Obviously correct to break the spin, but if spending a jiffie to react to signals was the only problem then it is not too severe. Add something to the commit message about how it was found/reported and about the severity of impact, etc? Otherwise, Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com> > Fixes regression from > commit 2def4ad99befa25775dd2f714fdd4d92faec6e34 [v4.2] > Author: Chris Wilson <chris at chris-wilson.co.uk> > Date: Tue Apr 7 16:20:41 2015 +0100 > > drm/i915: Optimistically spin for the request completion > > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk> > Cc: Jens Axboe <axboe at kernel.dk> > Cc; "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin at intel.com> > Cc: Daniel Vetter <daniel.vetter at ffwll.ch> > Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com> > Cc: Eero Tamminen <eero.t.tamminen at intel.com> > Cc: "Rantala, Valtteri" <valtteri.rantala at intel.com> > Cc: stable at kernel.vger.org > --- > drivers/gpu/drm/i915/i915_gem.c | 13 ++++++++----- > 1 file changed, 8 insertions(+), 5 deletions(-) > > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c > index 5cf4a1998273..740530c571d1 100644 > --- a/drivers/gpu/drm/i915/i915_gem.c > +++ b/drivers/gpu/drm/i915/i915_gem.c > @@ -1146,7 +1146,7 @@ static bool missed_irq(struct drm_i915_private > *dev_priv, > return test_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings); > } > > -static int __i915_spin_request(struct drm_i915_gem_request *req) > +static int __i915_spin_request(struct drm_i915_gem_request *req, int state) > { > unsigned long timeout; > > @@ -1158,6 +1158,9 @@ static int __i915_spin_request(struct > drm_i915_gem_request *req) > if (i915_gem_request_completed(req, true)) > return 0; > > + if (signal_pending_state(state, current)) > + break; > + > if (time_after_eq(jiffies, timeout)) > break; > > @@ -1197,6 +1200,7 @@ int __i915_wait_request(struct drm_i915_gem_request > *req, > struct drm_i915_private *dev_priv = dev->dev_private; > const bool irq_test_in_progress = > ACCESS_ONCE(dev_priv->gpu_error.test_irq_rings) & > intel_ring_flag(ring); > + int state = interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE; > DEFINE_WAIT(wait); > unsigned long timeout_expire; > s64 before, now; > @@ -1221,7 +1225,7 @@ int __i915_wait_request(struct drm_i915_gem_request > *req, > before = ktime_get_raw_ns(); > > /* Optimistic spin for the next jiffie before touching IRQs */ > - ret = __i915_spin_request(req); > + ret = __i915_spin_request(req, state); > if (ret == 0) > goto out; > > @@ -1233,8 +1237,7 @@ int __i915_wait_request(struct drm_i915_gem_request > *req, > for (;;) { > struct timer_list timer; > > - prepare_to_wait(&ring->irq_queue, &wait, > - interruptible ? TASK_INTERRUPTIBLE : > TASK_UNINTERRUPTIBLE); > + prepare_to_wait(&ring->irq_queue, &wait, state); > > /* We need to check whether any gpu reset happened in between > * the caller grabbing the seqno and now ... */ > @@ -1252,7 +1255,7 @@ int __i915_wait_request(struct drm_i915_gem_request > *req, > break; > } > > - if (interruptible && signal_pending(current)) { > + if (signal_pending_state(state, current)) { > ret = -ERESTARTSYS; > break; > } >