[PATCH v4] drm/i915/gt: Retry RING_HEAD reset until it get sticks

[Gote, Nitin R]

Hi Matt,

> -----Original Message-----
> From: Roper, Matthew D <matthew.d.roper at intel.com>
> Sent: Wednesday, October 16, 2024 5:23 AM
> To: Gote, Nitin R <nitin.r.gote at intel.com>
> Cc: intel-gfx at lists.freedesktop.org; Shyti, Andi <andi.shyti at intel.com>; Wilson,
> Chris P <chris.p.wilson at intel.com>; Das, Nirmoy <nirmoy.das at intel.com>;
> Chris Wilson <chris.p.wilson at linux.intel.com>
> Subject: Re: [PATCH v4] drm/i915/gt: Retry RING_HEAD reset until it get sticks
> 
> On Tue, Oct 15, 2024 at 08:27:10PM +0530, Nitin Gote wrote:
> > we see an issue where resets fails because the engine resumes from an
> > incorrect RING_HEAD. Since the RING_HEAD doesn't point to the
> > remaining requests to re-run, but may instead point into the
> > uninitialised portion of the ring, the GPU may be then fed invalid
> > instructions from a privileged context, oft pushing the GPU into an
> > unrecoverable hang.
> >
> > If at first the write doesn't succeed, try, try again.
> >
> > v2: Avoid unnecessary timeout macro (Andi)
> >
> > v3: Correct comment format (Andi)
> >
> > v4: Make it generic for all platform as it won't impact (Chris)
> >
> > Link: https://gitlab.freedesktop.org/drm/intel/-/issues/5432
> > Testcase: igt/i915_selftest/hangcheck
> 
> The referenced HSW-specific gitlab issue was closed in 2022 and hadn't been
> active for a while before that.  This patch from Chris was originally posted as an
> attachment on that gitlab issue asking if it helped, but nobody responded that it
> did/didn't improve the situation so it may or may not have been relevant to
> what was originally reported in that ticket.
> 
> Looking in cibuglog, the most similar failures I see today are the ones getting
> associated with issue #12310.  I.e.,
> 
>   <3> [220.415493] i915 0000:00:02.0: [drm] *ERROR* failed to set rcs0
>   head to zero ctl 00000000 head 00001db8 tail 00000000 start 7fffa000
> 
> Are you trying to solve that CI issue or is there a different user-submitted report
> somewhere that this patch is trying to address?
> 
> 
> Matt
> 

Yes. This patch is for https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/12310
I will update the link.

- Nitin

> 
> > Signed-off-by: Chris Wilson <chris.p.wilson at linux.intel.com>
> > Signed-off-by: Nitin Gote <nitin.r.gote at intel.com>
> > ---
> >  .../gpu/drm/i915/gt/intel_ring_submission.c   | 31 ++++++++++++++++---
> >  1 file changed, 27 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> > b/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> > index 72277bc8322e..b6b25fe22cb8 100644
> > --- a/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> > +++ b/drivers/gpu/drm/i915/gt/intel_ring_submission.c
> > @@ -192,6 +192,7 @@ static bool stop_ring(struct intel_engine_cs
> > *engine)  static int xcs_resume(struct intel_engine_cs *engine)  {
> >  	struct intel_ring *ring = engine->legacy.ring;
> > +	ktime_t kt;
> >
> >  	ENGINE_TRACE(engine, "ring:{HEAD:%04x, TAIL:%04x}\n",
> >  		     ring->head, ring->tail);
> > @@ -230,9 +231,27 @@ static int xcs_resume(struct intel_engine_cs
> *engine)
> >  	set_pp_dir(engine);
> >
> >  	/* First wake the ring up to an empty/idle ring */
> > -	ENGINE_WRITE_FW(engine, RING_HEAD, ring->head);
> > +	for ((kt) = ktime_get() + (2 * NSEC_PER_MSEC);
> > +			ktime_before(ktime_get(), (kt)); cpu_relax()) {
> > +		/*
> > +		 * In case of resets fails because engine resumes from
> > +		 * incorrect RING_HEAD and then GPU may be then fed
> > +		 * to invalid instrcutions, which may lead to unrecoverable
> > +		 * hang. So at first write doesn't succeed then try again.
> > +		 */
> > +		ENGINE_WRITE_FW(engine, RING_HEAD, ring->head);
> > +		if (ENGINE_READ_FW(engine, RING_HEAD) == ring->head)
> > +			break;
> > +	}
> > +
> >  	ENGINE_WRITE_FW(engine, RING_TAIL, ring->head);
> > -	ENGINE_POSTING_READ(engine, RING_TAIL);
> > +	if (ENGINE_READ_FW(engine, RING_HEAD) !=
> ENGINE_READ_FW(engine, RING_TAIL)) {
> > +		ENGINE_TRACE(engine, "failed to reset empty ring: [%x, %x]:
> %x\n",
> > +			     ENGINE_READ_FW(engine, RING_HEAD),
> > +			     ENGINE_READ_FW(engine, RING_TAIL),
> > +			     ring->head);
> > +		goto err;
> > +	}
> >
> >  	ENGINE_WRITE_FW(engine, RING_CTL,
> >  			RING_CTL_SIZE(ring->size) | RING_VALID); @@ -241,12
> +260,16 @@
> > static int xcs_resume(struct intel_engine_cs *engine)
> >  	if (__intel_wait_for_register_fw(engine->uncore,
> >  					 RING_CTL(engine->mmio_base),
> >  					 RING_VALID, RING_VALID,
> > -					 5000, 0, NULL))
> > +					 5000, 0, NULL)) {
> > +		ENGINE_TRACE(engine, "failed to restart\n");
> >  		goto err;
> > +	}
> >
> > -	if (GRAPHICS_VER(engine->i915) > 2)
> > +	if (GRAPHICS_VER(engine->i915) > 2) {
> >  		ENGINE_WRITE_FW(engine,
> >  				RING_MI_MODE,
> _MASKED_BIT_DISABLE(STOP_RING));
> > +		ENGINE_POSTING_READ(engine, RING_MI_MODE);
> > +	}
> >
> >  	/* Now awake, let it get started */
> >  	if (ring->tail != ring->head) {
> > --
> > 2.25.1
> >
> 
> --
> Matt Roper
> Graphics Software Engineer
> Linux GPU Platform Enablement
> Intel Corporation