Quoting Mika Kuoppala (2018-03-02 15:50:53)
> Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
>
> > During reset/wedging, we have to clean up the requests on the timeline
> > and flush the pending interrupt state. Currently, we are abusing the irq
> > disabling of the timeline spinlock to protect the irq state in
> > conjunction to the engine's timeline requests, but this is accidental
> > and conflates the spinlock with the irq state. A baffling state of
> > affairs for the reader.
> >
> > Instead, explicitly disable irqs over the critical section, and separate
> > modifying the irq state from the timeline's requests.
> >
> > Suggested-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> > Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> > Cc: Michel Thierry <michel.thierry@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/intel_lrc.c | 21 +++++++++++++++------
> > 1 file changed, 15 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> > index 0482e54c94f0..7d1109aceabb 100644
> > --- a/drivers/gpu/drm/i915/intel_lrc.c
> > +++ b/drivers/gpu/drm/i915/intel_lrc.c
> > @@ -689,11 +689,13 @@ static void execlists_cancel_requests(struct intel_engine_cs *engine)
> >
> > GEM_TRACE("%s\n", engine->name);
> >
> > - spin_lock_irqsave(&engine->timeline->lock, flags);
> > + local_irq_save(flags);
>
> Chris explained in irc that this is for lockdep only. It was a bit
> confusing as we already are guaranteed exclusive access to
> state by tasklet being killed and dead at this point.
>
> I think this warrants a comment that this is to soothe lockdep.
/*
* Before we call engine->cancel_requests(), we should have exclusive
* access to the submission state. This is arranged for us by the caller
* disabling the interrupt generation, the tasklet and other threads
* that may then access the same state, giving us a free hand to
* reset state. However, we still need to let lockdep be aware that
* we know this state may be accessed in hardirq context, so we
* disable the irq around this manipulation and we want to keep
* the spinlock focused on its duties and not accidentally conflate
* coverage to the submission's irq state. (Similarly, although we
* shouldn't need to disable irq around the manipulation of the
* submission's irq state, we also wish to remind ourselves that
* it is irq state.)
*/
> >
> > /* Cancel the requests on the HW and clear the ELSP tracker. */
> > execlists_cancel_port_requests(execlists);
> >
> > + spin_lock(&engine->timeline->lock);
> > @@ -1618,10 +1622,11 @@ static void reset_common_ring(struct intel_engine_cs *engine,
> > GEM_TRACE("%s seqno=%x\n",
> > engine->name, request ? request->global_seqno : 0);
> >
> > - spin_lock_irqsave(&engine->timeline->lock, flags);
/* See execlists_cancel_requests() for the irq/spinlock split. */
> > + local_irq_save(flags);
Good?
-Chris
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