[CI] drm/i915/execlists: Prevent GPU death on ELSP[1] promotion to idle context
diff mbox series

Message ID 20200327112653.14362-1-chris@chris-wilson.co.uk
State New
Headers show
Series
  • [CI] drm/i915/execlists: Prevent GPU death on ELSP[1] promotion to idle context
Related show

Commit Message

Chris Wilson March 27, 2020, 11:26 a.m. UTC
In what seems remarkably similar to the w/a required to not reload an
idle context with HEAD==TAIL, it appears we must prevent the HW from
switching to an idle context in ELSP[1], while simultaneously trying to
preempt the HW to run another context and a continuation of the idle
context (which is no longer idle).

  process_csb: vecs0: cs-irq head=0, tail=1
  process_csb: vecs0: csb[1]: status=0x00000882:0x00000020
  trace_ports: vecs0: preempted { 8c0:30!, 0:0 }
  trace_ports: vecs0: promote { 8b2:32!, 8c0:30 }
  trace_ports: vecs0: submit { 8b8:32, 8c0:32 }
  process_csb: vecs0: cs-irq head=1, tail=2
  process_csb: vecs0: csb[2]: status=0x00000814:0x00000040
  trace_ports: vecs0: completed { 8b2:32!, 8c0:30 }
  process_csb: vecs0: cs-irq head=2, tail=5
  process_csb: vecs0: csb[3]: status=0x00000812:0x00000020
  trace_ports: vecs0: preempted { 8c0:30!, 0:0 }
  trace_ports: vecs0: promote { 8b8:32!, 8c0:32 }
  process_csb: vecs0: csb[4]: status=0x00000814:0x00000060
  trace_ports: vecs0: completed { 8b8:32!, 8c0:32 }
  process_csb: vecs0: csb[5]: status=0x00000818:0x00000020
  trace_ports: vecs0: completed { 8c0:32, 0:0 }
  process_csb: vecs0: ring:{start:0x00021000, head:03f8, tail:03f8, ctl:00000000, mode:00000200}
  process_csb: vecs0: rq:{start:00021000, head:03c0, tail:0400, seqno:8c0:32, hwsp:30},
  process_csb: vecs0: ctx:{start:00021000, head:03f8, tail:03f8},
  process_csb: GEM_BUG_ON("context completed before request")

Fortunately, we just so happen to have a semaphore in place to prevent
the ring HEAD from proceeding past the end of a request that we can use
to fix the HEAD in position as we reprogram ELSP.

Closes: https://gitlab.freedesktop.org/drm/intel/issues/1501
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
---
 drivers/gpu/drm/i915/gt/intel_gt_irq.c |  2 +
 drivers/gpu/drm/i915/gt/intel_lrc.c    | 72 +++++++++++++-------------
 2 files changed, 38 insertions(+), 36 deletions(-)

Comments

Tvrtko Ursulin March 27, 2020, 3:59 p.m. UTC | #1
On 27/03/2020 11:26, Chris Wilson wrote:
> In what seems remarkably similar to the w/a required to not reload an
> idle context with HEAD==TAIL, it appears we must prevent the HW from
> switching to an idle context in ELSP[1], while simultaneously trying to
> preempt the HW to run another context and a continuation of the idle
> context (which is no longer idle).
> 
>    process_csb: vecs0: cs-irq head=0, tail=1
>    process_csb: vecs0: csb[1]: status=0x00000882:0x00000020
>    trace_ports: vecs0: preempted { 8c0:30!, 0:0 }
>    trace_ports: vecs0: promote { 8b2:32!, 8c0:30 }
>    trace_ports: vecs0: submit { 8b8:32, 8c0:32 }
>    process_csb: vecs0: cs-irq head=1, tail=2
>    process_csb: vecs0: csb[2]: status=0x00000814:0x00000040
>    trace_ports: vecs0: completed { 8b2:32!, 8c0:30 }
>    process_csb: vecs0: cs-irq head=2, tail=5
>    process_csb: vecs0: csb[3]: status=0x00000812:0x00000020
>    trace_ports: vecs0: preempted { 8c0:30!, 0:0 }
>    trace_ports: vecs0: promote { 8b8:32!, 8c0:32 }
>    process_csb: vecs0: csb[4]: status=0x00000814:0x00000060
>    trace_ports: vecs0: completed { 8b8:32!, 8c0:32 }
>    process_csb: vecs0: csb[5]: status=0x00000818:0x00000020
>    trace_ports: vecs0: completed { 8c0:32, 0:0 }
>    process_csb: vecs0: ring:{start:0x00021000, head:03f8, tail:03f8, ctl:00000000, mode:00000200}
>    process_csb: vecs0: rq:{start:00021000, head:03c0, tail:0400, seqno:8c0:32, hwsp:30},
>    process_csb: vecs0: ctx:{start:00021000, head:03f8, tail:03f8},
>    process_csb: GEM_BUG_ON("context completed before request")
> 
> Fortunately, we just so happen to have a semaphore in place to prevent
> the ring HEAD from proceeding past the end of a request that we can use
> to fix the HEAD in position as we reprogram ELSP.
> 
> Closes: https://gitlab.freedesktop.org/drm/intel/issues/1501
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> ---
>   drivers/gpu/drm/i915/gt/intel_gt_irq.c |  2 +
>   drivers/gpu/drm/i915/gt/intel_lrc.c    | 72 +++++++++++++-------------
>   2 files changed, 38 insertions(+), 36 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_irq.c b/drivers/gpu/drm/i915/gt/intel_gt_irq.c
> index f0e7fd95165a..be3817d99908 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt_irq.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gt_irq.c
> @@ -24,6 +24,8 @@ cs_irq_handler(struct intel_engine_cs *engine, u32 iir)
>   {
>   	bool tasklet = false;
>   
> +	ENGINE_TRACE(engine, "iir: %04x\n", iir);
> +
>   	if (unlikely(iir & GT_CS_MASTER_ERROR_INTERRUPT)) {
>   		u32 eir;
>   
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index b12355048501..53650b452bc9 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -1854,7 +1854,7 @@ static inline void clear_ports(struct i915_request **ports, int count)
>   	memset_p((void **)ports, NULL, count);
>   }
>   
> -static void execlists_dequeue(struct intel_engine_cs *engine)
> +static bool execlists_dequeue(struct intel_engine_cs *engine)
>   {
>   	struct intel_engine_execlists * const execlists = &engine->execlists;
>   	struct i915_request **port = execlists->pending;
> @@ -1928,13 +1928,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>   				     execlists->queue_priority_hint);
>   			record_preemption(execlists);
>   
> -			/*
> -			 * Don't let the RING_HEAD advance past the breadcrumb
> -			 * as we unwind (and until we resubmit) so that we do
> -			 * not accidentally tell it to go backwards.
> -			 */
> -			ring_set_paused(engine, 1);
> -
>   			/*
>   			 * Note that we have not stopped the GPU at this point,
>   			 * so we are unwinding the incomplete requests as they
> @@ -1954,7 +1947,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>   				     last->sched.attr.priority,
>   				     execlists->queue_priority_hint);
>   
> -			ring_set_paused(engine, 1);
>   			defer_active(engine);
>   
>   			/*
> @@ -1988,7 +1980,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>   				 * of timeslices, our queue might be.
>   				 */
>   				start_timeslice(engine);
> -				return;
> +				return false;
>   			}
>   		}
>   	}
> @@ -2021,9 +2013,10 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>   			}
>   
>   			if (last && !can_merge_rq(last, rq)) {
> +				/* leave this for another sibling */
>   				spin_unlock(&ve->base.active.lock);
>   				start_timeslice(engine);
> -				return; /* leave this for another sibling */
> +				return false;
>   			}
>   
>   			ENGINE_TRACE(engine,
> @@ -2193,32 +2186,31 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>   	 * interrupt for secondary ports).
>   	 */
>   	execlists->queue_priority_hint = queue_prio(execlists);
> +	if (!submit)
> +		return false;
>   
> -	if (submit) {
> -		*port = execlists_schedule_in(last, port - execlists->pending);
> -		execlists->switch_priority_hint =
> -			switch_prio(engine, *execlists->pending);
> +	*port = execlists_schedule_in(last, port - execlists->pending);
> +	execlists->switch_priority_hint =
> +		switch_prio(engine, *execlists->pending);
>   
> -		/*
> -		 * Skip if we ended up with exactly the same set of requests,
> -		 * e.g. trying to timeslice a pair of ordered contexts
> -		 */
> -		if (!memcmp(active, execlists->pending,
> -			    (port - execlists->pending + 1) * sizeof(*port))) {
> -			do
> -				execlists_schedule_out(fetch_and_zero(port));
> -			while (port-- != execlists->pending);
> -
> -			goto skip_submit;
> -		}
> -		clear_ports(port + 1, last_port - port);
> +	/*
> +	 * Skip if we ended up with exactly the same set of requests,
> +	 * e.g. trying to timeslice a pair of ordered contexts
> +	 */
> +	if (!memcmp(active, execlists->pending,
> +		    (port - execlists->pending + 1) * sizeof(*port))) {
> +		do
> +			execlists_schedule_out(fetch_and_zero(port));
> +		while (port-- != execlists->pending);
>   
> -		execlists_submit_ports(engine);
> -		set_preempt_timeout(engine, *active);
> -	} else {
> -skip_submit:
> -		ring_set_paused(engine, 0);
> +		return false;
>   	}
> +	clear_ports(port + 1, last_port - port);
> +
> +	execlists_submit_ports(engine);
> +	set_preempt_timeout(engine, *active);
> +	tasklet_hi_schedule(&execlists->tasklet); /* lost interrupt */
> +	return true;
>   }
>   
>   static void
> @@ -2478,7 +2470,16 @@ static void __execlists_submission_tasklet(struct intel_engine_cs *const engine)
>   	lockdep_assert_held(&engine->active.lock);
>   	if (!READ_ONCE(engine->execlists.pending[0])) {
>   		rcu_read_lock(); /* protect peeking at execlists->active */
> -		execlists_dequeue(engine);
> +
> +		/*
> +		 * Don't let the RING_HEAD advance past the breadcrumb
> +		 * as we unwind (and until we resubmit) so that we do
> +		 * not accidentally tell it to go backwards.
> +		 */
> +		ring_set_paused(engine, 1);
> +		if (!execlists_dequeue(engine))
> +			ring_set_paused(engine, 0);
> +
>   		rcu_read_unlock();
>   	}
>   }
> @@ -2816,8 +2817,7 @@ static void execlists_reset(struct intel_engine_cs *engine, const char *msg)
>   	ring_set_paused(engine, 1); /* Freeze the current request in place */
>   	if (execlists_capture(engine))
>   		intel_engine_reset(engine, msg);
> -	else
> -		ring_set_paused(engine, 0);
> +	ring_set_paused(engine, 0);
>   
>   	tasklet_enable(&engine->execlists.tasklet);
>   	clear_and_wake_up_bit(bit, lock);
> 

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko
Chris Wilson March 27, 2020, 4:47 p.m. UTC | #2
Quoting Tvrtko Ursulin (2020-03-27 15:59:45)
> 
> On 27/03/2020 11:26, Chris Wilson wrote:
> > In what seems remarkably similar to the w/a required to not reload an
> > idle context with HEAD==TAIL, it appears we must prevent the HW from
> > switching to an idle context in ELSP[1], while simultaneously trying to
> > preempt the HW to run another context and a continuation of the idle
> > context (which is no longer idle).
> > 
> >    process_csb: vecs0: cs-irq head=0, tail=1
> >    process_csb: vecs0: csb[1]: status=0x00000882:0x00000020
> >    trace_ports: vecs0: preempted { 8c0:30!, 0:0 }
> >    trace_ports: vecs0: promote { 8b2:32!, 8c0:30 }
> >    trace_ports: vecs0: submit { 8b8:32, 8c0:32 }
> >    process_csb: vecs0: cs-irq head=1, tail=2
> >    process_csb: vecs0: csb[2]: status=0x00000814:0x00000040
> >    trace_ports: vecs0: completed { 8b2:32!, 8c0:30 }
> >    process_csb: vecs0: cs-irq head=2, tail=5
> >    process_csb: vecs0: csb[3]: status=0x00000812:0x00000020
> >    trace_ports: vecs0: preempted { 8c0:30!, 0:0 }
> >    trace_ports: vecs0: promote { 8b8:32!, 8c0:32 }
> >    process_csb: vecs0: csb[4]: status=0x00000814:0x00000060
> >    trace_ports: vecs0: completed { 8b8:32!, 8c0:32 }
> >    process_csb: vecs0: csb[5]: status=0x00000818:0x00000020
> >    trace_ports: vecs0: completed { 8c0:32, 0:0 }
> >    process_csb: vecs0: ring:{start:0x00021000, head:03f8, tail:03f8, ctl:00000000, mode:00000200}
> >    process_csb: vecs0: rq:{start:00021000, head:03c0, tail:0400, seqno:8c0:32, hwsp:30},
> >    process_csb: vecs0: ctx:{start:00021000, head:03f8, tail:03f8},
> >    process_csb: GEM_BUG_ON("context completed before request")
> > 
> > Fortunately, we just so happen to have a semaphore in place to prevent
> > the ring HEAD from proceeding past the end of a request that we can use
> > to fix the HEAD in position as we reprogram ELSP.
> > 
> > Closes: https://gitlab.freedesktop.org/drm/intel/issues/1501
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> > Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> > ---
> >   drivers/gpu/drm/i915/gt/intel_gt_irq.c |  2 +
> >   drivers/gpu/drm/i915/gt/intel_lrc.c    | 72 +++++++++++++-------------
> >   2 files changed, 38 insertions(+), 36 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_irq.c b/drivers/gpu/drm/i915/gt/intel_gt_irq.c
> > index f0e7fd95165a..be3817d99908 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_gt_irq.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_gt_irq.c
> > @@ -24,6 +24,8 @@ cs_irq_handler(struct intel_engine_cs *engine, u32 iir)
> >   {
> >       bool tasklet = false;
> >   
> > +     ENGINE_TRACE(engine, "iir: %04x\n", iir);
> > +
> >       if (unlikely(iir & GT_CS_MASTER_ERROR_INTERRUPT)) {
> >               u32 eir;
> >   
> > diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> > index b12355048501..53650b452bc9 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> > @@ -1854,7 +1854,7 @@ static inline void clear_ports(struct i915_request **ports, int count)
> >       memset_p((void **)ports, NULL, count);
> >   }
> >   
> > -static void execlists_dequeue(struct intel_engine_cs *engine)
> > +static bool execlists_dequeue(struct intel_engine_cs *engine)
> >   {
> >       struct intel_engine_execlists * const execlists = &engine->execlists;
> >       struct i915_request **port = execlists->pending;
> > @@ -1928,13 +1928,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> >                                    execlists->queue_priority_hint);
> >                       record_preemption(execlists);
> >   
> > -                     /*
> > -                      * Don't let the RING_HEAD advance past the breadcrumb
> > -                      * as we unwind (and until we resubmit) so that we do
> > -                      * not accidentally tell it to go backwards.
> > -                      */
> > -                     ring_set_paused(engine, 1);
> > -
> >                       /*
> >                        * Note that we have not stopped the GPU at this point,
> >                        * so we are unwinding the incomplete requests as they
> > @@ -1954,7 +1947,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> >                                    last->sched.attr.priority,
> >                                    execlists->queue_priority_hint);
> >   
> > -                     ring_set_paused(engine, 1);
> >                       defer_active(engine);
> >   
> >                       /*
> > @@ -1988,7 +1980,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> >                                * of timeslices, our queue might be.
> >                                */
> >                               start_timeslice(engine);
> > -                             return;
> > +                             return false;
> >                       }
> >               }
> >       }
> > @@ -2021,9 +2013,10 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> >                       }
> >   
> >                       if (last && !can_merge_rq(last, rq)) {
> > +                             /* leave this for another sibling */
> >                               spin_unlock(&ve->base.active.lock);
> >                               start_timeslice(engine);
> > -                             return; /* leave this for another sibling */
> > +                             return false;
> >                       }
> >   
> >                       ENGINE_TRACE(engine,
> > @@ -2193,32 +2186,31 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> >        * interrupt for secondary ports).
> >        */
> >       execlists->queue_priority_hint = queue_prio(execlists);
> > +     if (!submit)
> > +             return false;
> >   
> > -     if (submit) {
> > -             *port = execlists_schedule_in(last, port - execlists->pending);
> > -             execlists->switch_priority_hint =
> > -                     switch_prio(engine, *execlists->pending);
> > +     *port = execlists_schedule_in(last, port - execlists->pending);
> > +     execlists->switch_priority_hint =
> > +             switch_prio(engine, *execlists->pending);
> >   
> > -             /*
> > -              * Skip if we ended up with exactly the same set of requests,
> > -              * e.g. trying to timeslice a pair of ordered contexts
> > -              */
> > -             if (!memcmp(active, execlists->pending,
> > -                         (port - execlists->pending + 1) * sizeof(*port))) {
> > -                     do
> > -                             execlists_schedule_out(fetch_and_zero(port));
> > -                     while (port-- != execlists->pending);
> > -
> > -                     goto skip_submit;
> > -             }
> > -             clear_ports(port + 1, last_port - port);
> > +     /*
> > +      * Skip if we ended up with exactly the same set of requests,
> > +      * e.g. trying to timeslice a pair of ordered contexts
> > +      */
> > +     if (!memcmp(active, execlists->pending,
> > +                 (port - execlists->pending + 1) * sizeof(*port))) {
> > +             do
> > +                     execlists_schedule_out(fetch_and_zero(port));
> > +             while (port-- != execlists->pending);
> >   
> > -             execlists_submit_ports(engine);
> > -             set_preempt_timeout(engine, *active);
> > -     } else {
> > -skip_submit:
> > -             ring_set_paused(engine, 0);
> > +             return false;
> >       }
> > +     clear_ports(port + 1, last_port - port);
> > +
> > +     execlists_submit_ports(engine);
> > +     set_preempt_timeout(engine, *active);
> > +     tasklet_hi_schedule(&execlists->tasklet); /* lost interrupt */
> > +     return true;
> >   }
> >   
> >   static void
> > @@ -2478,7 +2470,16 @@ static void __execlists_submission_tasklet(struct intel_engine_cs *const engine)
> >       lockdep_assert_held(&engine->active.lock);
> >       if (!READ_ONCE(engine->execlists.pending[0])) {
> >               rcu_read_lock(); /* protect peeking at execlists->active */
> > -             execlists_dequeue(engine);
> > +
> > +             /*
> > +              * Don't let the RING_HEAD advance past the breadcrumb
> > +              * as we unwind (and until we resubmit) so that we do
> > +              * not accidentally tell it to go backwards.
> > +              */
> > +             ring_set_paused(engine, 1);
> > +             if (!execlists_dequeue(engine))
> > +                     ring_set_paused(engine, 0);
> > +
> >               rcu_read_unlock();
> >       }
> >   }
> > @@ -2816,8 +2817,7 @@ static void execlists_reset(struct intel_engine_cs *engine, const char *msg)
> >       ring_set_paused(engine, 1); /* Freeze the current request in place */
> >       if (execlists_capture(engine))
> >               intel_engine_reset(engine, msg);
> > -     else
> > -             ring_set_paused(engine, 0);
> > +     ring_set_paused(engine, 0);
> >   
> >       tasklet_enable(&engine->execlists.tasklet);
> >       clear_and_wake_up_bit(bit, lock);
> > 
> 
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

The problem appears to be that if we lite-restore into a context inside
the semaphore, it doesn't yield an arbitration point and we do not raise
a CSB event.

Out of the frying pan and into the fire.
-Chris
Mika Kuoppala March 27, 2020, 8:19 p.m. UTC | #3
Chris Wilson <chris@chris-wilson.co.uk> writes:

> Quoting Tvrtko Ursulin (2020-03-27 15:59:45)
>> 
>> On 27/03/2020 11:26, Chris Wilson wrote:
>> > In what seems remarkably similar to the w/a required to not reload an
>> > idle context with HEAD==TAIL, it appears we must prevent the HW from
>> > switching to an idle context in ELSP[1], while simultaneously trying to
>> > preempt the HW to run another context and a continuation of the idle
>> > context (which is no longer idle).
>> > 
>> >    process_csb: vecs0: cs-irq head=0, tail=1
>> >    process_csb: vecs0: csb[1]: status=0x00000882:0x00000020
>> >    trace_ports: vecs0: preempted { 8c0:30!, 0:0 }
>> >    trace_ports: vecs0: promote { 8b2:32!, 8c0:30 }
>> >    trace_ports: vecs0: submit { 8b8:32, 8c0:32 }
>> >    process_csb: vecs0: cs-irq head=1, tail=2
>> >    process_csb: vecs0: csb[2]: status=0x00000814:0x00000040
>> >    trace_ports: vecs0: completed { 8b2:32!, 8c0:30 }
>> >    process_csb: vecs0: cs-irq head=2, tail=5
>> >    process_csb: vecs0: csb[3]: status=0x00000812:0x00000020
>> >    trace_ports: vecs0: preempted { 8c0:30!, 0:0 }
>> >    trace_ports: vecs0: promote { 8b8:32!, 8c0:32 }
>> >    process_csb: vecs0: csb[4]: status=0x00000814:0x00000060
>> >    trace_ports: vecs0: completed { 8b8:32!, 8c0:32 }
>> >    process_csb: vecs0: csb[5]: status=0x00000818:0x00000020
>> >    trace_ports: vecs0: completed { 8c0:32, 0:0 }
>> >    process_csb: vecs0: ring:{start:0x00021000, head:03f8, tail:03f8, ctl:00000000, mode:00000200}
>> >    process_csb: vecs0: rq:{start:00021000, head:03c0, tail:0400, seqno:8c0:32, hwsp:30},
>> >    process_csb: vecs0: ctx:{start:00021000, head:03f8, tail:03f8},
>> >    process_csb: GEM_BUG_ON("context completed before request")
>> > 
>> > Fortunately, we just so happen to have a semaphore in place to prevent
>> > the ring HEAD from proceeding past the end of a request that we can use
>> > to fix the HEAD in position as we reprogram ELSP.
>> > 
>> > Closes: https://gitlab.freedesktop.org/drm/intel/issues/1501
>> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>> > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>> > Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
>> > ---
>> >   drivers/gpu/drm/i915/gt/intel_gt_irq.c |  2 +
>> >   drivers/gpu/drm/i915/gt/intel_lrc.c    | 72 +++++++++++++-------------
>> >   2 files changed, 38 insertions(+), 36 deletions(-)
>> > 
>> > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_irq.c b/drivers/gpu/drm/i915/gt/intel_gt_irq.c
>> > index f0e7fd95165a..be3817d99908 100644
>> > --- a/drivers/gpu/drm/i915/gt/intel_gt_irq.c
>> > +++ b/drivers/gpu/drm/i915/gt/intel_gt_irq.c
>> > @@ -24,6 +24,8 @@ cs_irq_handler(struct intel_engine_cs *engine, u32 iir)
>> >   {
>> >       bool tasklet = false;
>> >   
>> > +     ENGINE_TRACE(engine, "iir: %04x\n", iir);
>> > +
>> >       if (unlikely(iir & GT_CS_MASTER_ERROR_INTERRUPT)) {
>> >               u32 eir;
>> >   
>> > diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
>> > index b12355048501..53650b452bc9 100644
>> > --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
>> > +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
>> > @@ -1854,7 +1854,7 @@ static inline void clear_ports(struct i915_request **ports, int count)
>> >       memset_p((void **)ports, NULL, count);
>> >   }
>> >   
>> > -static void execlists_dequeue(struct intel_engine_cs *engine)
>> > +static bool execlists_dequeue(struct intel_engine_cs *engine)
>> >   {
>> >       struct intel_engine_execlists * const execlists = &engine->execlists;
>> >       struct i915_request **port = execlists->pending;
>> > @@ -1928,13 +1928,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>> >                                    execlists->queue_priority_hint);
>> >                       record_preemption(execlists);
>> >   
>> > -                     /*
>> > -                      * Don't let the RING_HEAD advance past the breadcrumb
>> > -                      * as we unwind (and until we resubmit) so that we do
>> > -                      * not accidentally tell it to go backwards.
>> > -                      */
>> > -                     ring_set_paused(engine, 1);
>> > -
>> >                       /*
>> >                        * Note that we have not stopped the GPU at this point,
>> >                        * so we are unwinding the incomplete requests as they
>> > @@ -1954,7 +1947,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>> >                                    last->sched.attr.priority,
>> >                                    execlists->queue_priority_hint);
>> >   
>> > -                     ring_set_paused(engine, 1);
>> >                       defer_active(engine);
>> >   
>> >                       /*
>> > @@ -1988,7 +1980,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>> >                                * of timeslices, our queue might be.
>> >                                */
>> >                               start_timeslice(engine);
>> > -                             return;
>> > +                             return false;
>> >                       }
>> >               }
>> >       }
>> > @@ -2021,9 +2013,10 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>> >                       }
>> >   
>> >                       if (last && !can_merge_rq(last, rq)) {
>> > +                             /* leave this for another sibling */
>> >                               spin_unlock(&ve->base.active.lock);
>> >                               start_timeslice(engine);
>> > -                             return; /* leave this for another sibling */
>> > +                             return false;
>> >                       }
>> >   
>> >                       ENGINE_TRACE(engine,
>> > @@ -2193,32 +2186,31 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
>> >        * interrupt for secondary ports).
>> >        */
>> >       execlists->queue_priority_hint = queue_prio(execlists);
>> > +     if (!submit)
>> > +             return false;
>> >   
>> > -     if (submit) {
>> > -             *port = execlists_schedule_in(last, port - execlists->pending);
>> > -             execlists->switch_priority_hint =
>> > -                     switch_prio(engine, *execlists->pending);
>> > +     *port = execlists_schedule_in(last, port - execlists->pending);
>> > +     execlists->switch_priority_hint =
>> > +             switch_prio(engine, *execlists->pending);
>> >   
>> > -             /*
>> > -              * Skip if we ended up with exactly the same set of requests,
>> > -              * e.g. trying to timeslice a pair of ordered contexts
>> > -              */
>> > -             if (!memcmp(active, execlists->pending,
>> > -                         (port - execlists->pending + 1) * sizeof(*port))) {
>> > -                     do
>> > -                             execlists_schedule_out(fetch_and_zero(port));
>> > -                     while (port-- != execlists->pending);
>> > -
>> > -                     goto skip_submit;
>> > -             }
>> > -             clear_ports(port + 1, last_port - port);
>> > +     /*
>> > +      * Skip if we ended up with exactly the same set of requests,
>> > +      * e.g. trying to timeslice a pair of ordered contexts
>> > +      */
>> > +     if (!memcmp(active, execlists->pending,
>> > +                 (port - execlists->pending + 1) * sizeof(*port))) {
>> > +             do
>> > +                     execlists_schedule_out(fetch_and_zero(port));
>> > +             while (port-- != execlists->pending);
>> >   
>> > -             execlists_submit_ports(engine);
>> > -             set_preempt_timeout(engine, *active);
>> > -     } else {
>> > -skip_submit:
>> > -             ring_set_paused(engine, 0);
>> > +             return false;
>> >       }
>> > +     clear_ports(port + 1, last_port - port);
>> > +
>> > +     execlists_submit_ports(engine);
>> > +     set_preempt_timeout(engine, *active);
>> > +     tasklet_hi_schedule(&execlists->tasklet); /* lost interrupt */
>> > +     return true;
>> >   }
>> >   
>> >   static void
>> > @@ -2478,7 +2470,16 @@ static void __execlists_submission_tasklet(struct intel_engine_cs *const engine)
>> >       lockdep_assert_held(&engine->active.lock);
>> >       if (!READ_ONCE(engine->execlists.pending[0])) {
>> >               rcu_read_lock(); /* protect peeking at execlists->active */
>> > -             execlists_dequeue(engine);
>> > +
>> > +             /*
>> > +              * Don't let the RING_HEAD advance past the breadcrumb
>> > +              * as we unwind (and until we resubmit) so that we do
>> > +              * not accidentally tell it to go backwards.
>> > +              */
>> > +             ring_set_paused(engine, 1);
>> > +             if (!execlists_dequeue(engine))
>> > +                     ring_set_paused(engine, 0);
>> > +
>> >               rcu_read_unlock();
>> >       }
>> >   }
>> > @@ -2816,8 +2817,7 @@ static void execlists_reset(struct intel_engine_cs *engine, const char *msg)
>> >       ring_set_paused(engine, 1); /* Freeze the current request in place */
>> >       if (execlists_capture(engine))
>> >               intel_engine_reset(engine, msg);
>> > -     else
>> > -             ring_set_paused(engine, 0);
>> > +     ring_set_paused(engine, 0);
>> >   
>> >       tasklet_enable(&engine->execlists.tasklet);
>> >       clear_and_wake_up_bit(bit, lock);
>> > 
>> 
>> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>
> The problem appears to be that if we lite-restore into a context inside
> the semaphore, it doesn't yield an arbitration point and we do not raise
> a CSB event.

Trying to make senses of it all...

we do not raise == the hardware does not raise?

So if it is about lite restoring, we can't workaround by always making
sure elsp[1] head != tail?

-Mika


>
> Out of the frying pan and into the fire.
> -Chris
> _______________________________________________
> Intel-gfx mailing list
> Intel-gfx@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/intel-gfx
Chris Wilson March 27, 2020, 8:32 p.m. UTC | #4
Quoting Mika Kuoppala (2020-03-27 20:19:15)
> Chris Wilson <chris@chris-wilson.co.uk> writes:
> 
> > Quoting Tvrtko Ursulin (2020-03-27 15:59:45)
> >> 
> >> On 27/03/2020 11:26, Chris Wilson wrote:
> >> > In what seems remarkably similar to the w/a required to not reload an
> >> > idle context with HEAD==TAIL, it appears we must prevent the HW from
> >> > switching to an idle context in ELSP[1], while simultaneously trying to
> >> > preempt the HW to run another context and a continuation of the idle
> >> > context (which is no longer idle).
> >> > 
> >> >    process_csb: vecs0: cs-irq head=0, tail=1
> >> >    process_csb: vecs0: csb[1]: status=0x00000882:0x00000020
> >> >    trace_ports: vecs0: preempted { 8c0:30!, 0:0 }
> >> >    trace_ports: vecs0: promote { 8b2:32!, 8c0:30 }
> >> >    trace_ports: vecs0: submit { 8b8:32, 8c0:32 }
> >> >    process_csb: vecs0: cs-irq head=1, tail=2
> >> >    process_csb: vecs0: csb[2]: status=0x00000814:0x00000040
> >> >    trace_ports: vecs0: completed { 8b2:32!, 8c0:30 }
> >> >    process_csb: vecs0: cs-irq head=2, tail=5
> >> >    process_csb: vecs0: csb[3]: status=0x00000812:0x00000020
> >> >    trace_ports: vecs0: preempted { 8c0:30!, 0:0 }
> >> >    trace_ports: vecs0: promote { 8b8:32!, 8c0:32 }
> >> >    process_csb: vecs0: csb[4]: status=0x00000814:0x00000060
> >> >    trace_ports: vecs0: completed { 8b8:32!, 8c0:32 }
> >> >    process_csb: vecs0: csb[5]: status=0x00000818:0x00000020
> >> >    trace_ports: vecs0: completed { 8c0:32, 0:0 }
> >> >    process_csb: vecs0: ring:{start:0x00021000, head:03f8, tail:03f8, ctl:00000000, mode:00000200}
> >> >    process_csb: vecs0: rq:{start:00021000, head:03c0, tail:0400, seqno:8c0:32, hwsp:30},
> >> >    process_csb: vecs0: ctx:{start:00021000, head:03f8, tail:03f8},
> >> >    process_csb: GEM_BUG_ON("context completed before request")
> >> > 
> >> > Fortunately, we just so happen to have a semaphore in place to prevent
> >> > the ring HEAD from proceeding past the end of a request that we can use
> >> > to fix the HEAD in position as we reprogram ELSP.
> >> > 
> >> > Closes: https://gitlab.freedesktop.org/drm/intel/issues/1501
> >> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> >> > Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> >> > Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
> >> > ---
> >> >   drivers/gpu/drm/i915/gt/intel_gt_irq.c |  2 +
> >> >   drivers/gpu/drm/i915/gt/intel_lrc.c    | 72 +++++++++++++-------------
> >> >   2 files changed, 38 insertions(+), 36 deletions(-)
> >> > 
> >> > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_irq.c b/drivers/gpu/drm/i915/gt/intel_gt_irq.c
> >> > index f0e7fd95165a..be3817d99908 100644
> >> > --- a/drivers/gpu/drm/i915/gt/intel_gt_irq.c
> >> > +++ b/drivers/gpu/drm/i915/gt/intel_gt_irq.c
> >> > @@ -24,6 +24,8 @@ cs_irq_handler(struct intel_engine_cs *engine, u32 iir)
> >> >   {
> >> >       bool tasklet = false;
> >> >   
> >> > +     ENGINE_TRACE(engine, "iir: %04x\n", iir);
> >> > +
> >> >       if (unlikely(iir & GT_CS_MASTER_ERROR_INTERRUPT)) {
> >> >               u32 eir;
> >> >   
> >> > diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> >> > index b12355048501..53650b452bc9 100644
> >> > --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> >> > +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> >> > @@ -1854,7 +1854,7 @@ static inline void clear_ports(struct i915_request **ports, int count)
> >> >       memset_p((void **)ports, NULL, count);
> >> >   }
> >> >   
> >> > -static void execlists_dequeue(struct intel_engine_cs *engine)
> >> > +static bool execlists_dequeue(struct intel_engine_cs *engine)
> >> >   {
> >> >       struct intel_engine_execlists * const execlists = &engine->execlists;
> >> >       struct i915_request **port = execlists->pending;
> >> > @@ -1928,13 +1928,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> >> >                                    execlists->queue_priority_hint);
> >> >                       record_preemption(execlists);
> >> >   
> >> > -                     /*
> >> > -                      * Don't let the RING_HEAD advance past the breadcrumb
> >> > -                      * as we unwind (and until we resubmit) so that we do
> >> > -                      * not accidentally tell it to go backwards.
> >> > -                      */
> >> > -                     ring_set_paused(engine, 1);
> >> > -
> >> >                       /*
> >> >                        * Note that we have not stopped the GPU at this point,
> >> >                        * so we are unwinding the incomplete requests as they
> >> > @@ -1954,7 +1947,6 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> >> >                                    last->sched.attr.priority,
> >> >                                    execlists->queue_priority_hint);
> >> >   
> >> > -                     ring_set_paused(engine, 1);
> >> >                       defer_active(engine);
> >> >   
> >> >                       /*
> >> > @@ -1988,7 +1980,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> >> >                                * of timeslices, our queue might be.
> >> >                                */
> >> >                               start_timeslice(engine);
> >> > -                             return;
> >> > +                             return false;
> >> >                       }
> >> >               }
> >> >       }
> >> > @@ -2021,9 +2013,10 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> >> >                       }
> >> >   
> >> >                       if (last && !can_merge_rq(last, rq)) {
> >> > +                             /* leave this for another sibling */
> >> >                               spin_unlock(&ve->base.active.lock);
> >> >                               start_timeslice(engine);
> >> > -                             return; /* leave this for another sibling */
> >> > +                             return false;
> >> >                       }
> >> >   
> >> >                       ENGINE_TRACE(engine,
> >> > @@ -2193,32 +2186,31 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> >> >        * interrupt for secondary ports).
> >> >        */
> >> >       execlists->queue_priority_hint = queue_prio(execlists);
> >> > +     if (!submit)
> >> > +             return false;
> >> >   
> >> > -     if (submit) {
> >> > -             *port = execlists_schedule_in(last, port - execlists->pending);
> >> > -             execlists->switch_priority_hint =
> >> > -                     switch_prio(engine, *execlists->pending);
> >> > +     *port = execlists_schedule_in(last, port - execlists->pending);
> >> > +     execlists->switch_priority_hint =
> >> > +             switch_prio(engine, *execlists->pending);
> >> >   
> >> > -             /*
> >> > -              * Skip if we ended up with exactly the same set of requests,
> >> > -              * e.g. trying to timeslice a pair of ordered contexts
> >> > -              */
> >> > -             if (!memcmp(active, execlists->pending,
> >> > -                         (port - execlists->pending + 1) * sizeof(*port))) {
> >> > -                     do
> >> > -                             execlists_schedule_out(fetch_and_zero(port));
> >> > -                     while (port-- != execlists->pending);
> >> > -
> >> > -                     goto skip_submit;
> >> > -             }
> >> > -             clear_ports(port + 1, last_port - port);
> >> > +     /*
> >> > +      * Skip if we ended up with exactly the same set of requests,
> >> > +      * e.g. trying to timeslice a pair of ordered contexts
> >> > +      */
> >> > +     if (!memcmp(active, execlists->pending,
> >> > +                 (port - execlists->pending + 1) * sizeof(*port))) {
> >> > +             do
> >> > +                     execlists_schedule_out(fetch_and_zero(port));
> >> > +             while (port-- != execlists->pending);
> >> >   
> >> > -             execlists_submit_ports(engine);
> >> > -             set_preempt_timeout(engine, *active);
> >> > -     } else {
> >> > -skip_submit:
> >> > -             ring_set_paused(engine, 0);
> >> > +             return false;
> >> >       }
> >> > +     clear_ports(port + 1, last_port - port);
> >> > +
> >> > +     execlists_submit_ports(engine);
> >> > +     set_preempt_timeout(engine, *active);
> >> > +     tasklet_hi_schedule(&execlists->tasklet); /* lost interrupt */
> >> > +     return true;
> >> >   }
> >> >   
> >> >   static void
> >> > @@ -2478,7 +2470,16 @@ static void __execlists_submission_tasklet(struct intel_engine_cs *const engine)
> >> >       lockdep_assert_held(&engine->active.lock);
> >> >       if (!READ_ONCE(engine->execlists.pending[0])) {
> >> >               rcu_read_lock(); /* protect peeking at execlists->active */
> >> > -             execlists_dequeue(engine);
> >> > +
> >> > +             /*
> >> > +              * Don't let the RING_HEAD advance past the breadcrumb
> >> > +              * as we unwind (and until we resubmit) so that we do
> >> > +              * not accidentally tell it to go backwards.
> >> > +              */
> >> > +             ring_set_paused(engine, 1);
> >> > +             if (!execlists_dequeue(engine))
> >> > +                     ring_set_paused(engine, 0);
> >> > +
> >> >               rcu_read_unlock();
> >> >       }
> >> >   }
> >> > @@ -2816,8 +2817,7 @@ static void execlists_reset(struct intel_engine_cs *engine, const char *msg)
> >> >       ring_set_paused(engine, 1); /* Freeze the current request in place */
> >> >       if (execlists_capture(engine))
> >> >               intel_engine_reset(engine, msg);
> >> > -     else
> >> > -             ring_set_paused(engine, 0);
> >> > +     ring_set_paused(engine, 0);
> >> >   
> >> >       tasklet_enable(&engine->execlists.tasklet);
> >> >       clear_and_wake_up_bit(bit, lock);
> >> > 
> >> 
> >> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> >
> > The problem appears to be that if we lite-restore into a context inside
> > the semaphore, it doesn't yield an arbitration point and we do not raise
> > a CSB event.
> 
> Trying to make senses of it all...
> 
> we do not raise == the hardware does not raise?

HW.
 
> So if it is about lite restoring, we can't workaround by always making
> sure elsp[1] head != tail?

No. The context we enter into ELSP[1] is still executing on the GPU and
hits HEAD==TAIL after we write the register, but before the GPU
processes the register.
-Chris

Patch
diff mbox series

diff --git a/drivers/gpu/drm/i915/gt/intel_gt_irq.c b/drivers/gpu/drm/i915/gt/intel_gt_irq.c
index f0e7fd95165a..be3817d99908 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_irq.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt_irq.c
@@ -24,6 +24,8 @@  cs_irq_handler(struct intel_engine_cs *engine, u32 iir)
 {
 	bool tasklet = false;
 
+	ENGINE_TRACE(engine, "iir: %04x\n", iir);
+
 	if (unlikely(iir & GT_CS_MASTER_ERROR_INTERRUPT)) {
 		u32 eir;
 
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
index b12355048501..53650b452bc9 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -1854,7 +1854,7 @@  static inline void clear_ports(struct i915_request **ports, int count)
 	memset_p((void **)ports, NULL, count);
 }
 
-static void execlists_dequeue(struct intel_engine_cs *engine)
+static bool execlists_dequeue(struct intel_engine_cs *engine)
 {
 	struct intel_engine_execlists * const execlists = &engine->execlists;
 	struct i915_request **port = execlists->pending;
@@ -1928,13 +1928,6 @@  static void execlists_dequeue(struct intel_engine_cs *engine)
 				     execlists->queue_priority_hint);
 			record_preemption(execlists);
 
-			/*
-			 * Don't let the RING_HEAD advance past the breadcrumb
-			 * as we unwind (and until we resubmit) so that we do
-			 * not accidentally tell it to go backwards.
-			 */
-			ring_set_paused(engine, 1);
-
 			/*
 			 * Note that we have not stopped the GPU at this point,
 			 * so we are unwinding the incomplete requests as they
@@ -1954,7 +1947,6 @@  static void execlists_dequeue(struct intel_engine_cs *engine)
 				     last->sched.attr.priority,
 				     execlists->queue_priority_hint);
 
-			ring_set_paused(engine, 1);
 			defer_active(engine);
 
 			/*
@@ -1988,7 +1980,7 @@  static void execlists_dequeue(struct intel_engine_cs *engine)
 				 * of timeslices, our queue might be.
 				 */
 				start_timeslice(engine);
-				return;
+				return false;
 			}
 		}
 	}
@@ -2021,9 +2013,10 @@  static void execlists_dequeue(struct intel_engine_cs *engine)
 			}
 
 			if (last && !can_merge_rq(last, rq)) {
+				/* leave this for another sibling */
 				spin_unlock(&ve->base.active.lock);
 				start_timeslice(engine);
-				return; /* leave this for another sibling */
+				return false;
 			}
 
 			ENGINE_TRACE(engine,
@@ -2193,32 +2186,31 @@  static void execlists_dequeue(struct intel_engine_cs *engine)
 	 * interrupt for secondary ports).
 	 */
 	execlists->queue_priority_hint = queue_prio(execlists);
+	if (!submit)
+		return false;
 
-	if (submit) {
-		*port = execlists_schedule_in(last, port - execlists->pending);
-		execlists->switch_priority_hint =
-			switch_prio(engine, *execlists->pending);
+	*port = execlists_schedule_in(last, port - execlists->pending);
+	execlists->switch_priority_hint =
+		switch_prio(engine, *execlists->pending);
 
-		/*
-		 * Skip if we ended up with exactly the same set of requests,
-		 * e.g. trying to timeslice a pair of ordered contexts
-		 */
-		if (!memcmp(active, execlists->pending,
-			    (port - execlists->pending + 1) * sizeof(*port))) {
-			do
-				execlists_schedule_out(fetch_and_zero(port));
-			while (port-- != execlists->pending);
-
-			goto skip_submit;
-		}
-		clear_ports(port + 1, last_port - port);
+	/*
+	 * Skip if we ended up with exactly the same set of requests,
+	 * e.g. trying to timeslice a pair of ordered contexts
+	 */
+	if (!memcmp(active, execlists->pending,
+		    (port - execlists->pending + 1) * sizeof(*port))) {
+		do
+			execlists_schedule_out(fetch_and_zero(port));
+		while (port-- != execlists->pending);
 
-		execlists_submit_ports(engine);
-		set_preempt_timeout(engine, *active);
-	} else {
-skip_submit:
-		ring_set_paused(engine, 0);
+		return false;
 	}
+	clear_ports(port + 1, last_port - port);
+
+	execlists_submit_ports(engine);
+	set_preempt_timeout(engine, *active);
+	tasklet_hi_schedule(&execlists->tasklet); /* lost interrupt */
+	return true;
 }
 
 static void
@@ -2478,7 +2470,16 @@  static void __execlists_submission_tasklet(struct intel_engine_cs *const engine)
 	lockdep_assert_held(&engine->active.lock);
 	if (!READ_ONCE(engine->execlists.pending[0])) {
 		rcu_read_lock(); /* protect peeking at execlists->active */
-		execlists_dequeue(engine);
+
+		/*
+		 * Don't let the RING_HEAD advance past the breadcrumb
+		 * as we unwind (and until we resubmit) so that we do
+		 * not accidentally tell it to go backwards.
+		 */
+		ring_set_paused(engine, 1);
+		if (!execlists_dequeue(engine))
+			ring_set_paused(engine, 0);
+
 		rcu_read_unlock();
 	}
 }
@@ -2816,8 +2817,7 @@  static void execlists_reset(struct intel_engine_cs *engine, const char *msg)
 	ring_set_paused(engine, 1); /* Freeze the current request in place */
 	if (execlists_capture(engine))
 		intel_engine_reset(engine, msg);
-	else
-		ring_set_paused(engine, 0);
+	ring_set_paused(engine, 0);
 
 	tasklet_enable(&engine->execlists.tasklet);
 	clear_and_wake_up_bit(bit, lock);