[PATCH v2 2/2] drm/i915/guc: Don't unblock a non-schedulable context

[Javier MV <javiermv@gmail.com>]

From: Javier MV <javiermv@duck.com>

guc_context_cancel_request() blocks the context, skips the request and
unblocks the context again. If the context gets banned meanwhile (the
blocked request hits a GuC context reset), guc_context_revoke() finds
the schedule disable of the block still pending, so it only sets the
preemption timeout to 1 ms and leaves the cancellation to the schedule
disable done handler. That handler clears SCHED_STATE_BANNED, and then
guc_context_unblock() finds nothing in context_cant_unblock() that
stops it from enabling scheduling again.

GuC then runs a banned context with a 1 ms preemption timeout and
resets it again at the first preemption. Seen on ADL-P: the second
reset notification was ignored, GuC sent G2H messages the driver
rejected (action 0x6000, -EOPNOTSUPP), the rcs0 heartbeat stopped and
the whole GT was reset, which also kills every other client's work.

Also check intel_context_is_schedulable(), whose CONTEXT_BANNED and
CONTEXT_EXITING flags stay set. Exiting contexts need it too: revoke
takes the same SCHED_STATE_BANNED path for them, so the same race can
re-enable a revoked context. The requests the replay put back in the
queue are then completed on resubmission, as for any banned context.

Found and fixed with Claude Code; details in the cover letter.

Fixes: 9888beaaf118 ("drm/i915/guc: Don't enable scheduling on a banned context, guc_id invalid, not registered")
Link: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/15301
Signed-off-by: Javier MV <javiermv@duck.com>
---
v2:
- Check !intel_context_is_schedulable() instead of
  intel_context_is_banned(): revoke takes the same path for exiting
  contexts (Sashiko).

 drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
index b2ffc6b..966c23e 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -3186,7 +3186,12 @@ static bool context_cant_unblock(struct intel_context *ce)
 {
 	lockdep_assert_held(&ce->guc_state.lock);
 
+	/*
+	 * SCHED_STATE_BANNED alone isn't enough: the sched disable done
+	 * handler clears it. Revoke sets it for exiting contexts too.
+	 */
 	return (ce->guc_state.sched_state & SCHED_STATE_NO_UNBLOCK) ||
+		!intel_context_is_schedulable(ce) ||
 		context_guc_id_invalid(ce) ||
 		!ctx_id_mapped(ce_to_guc(ce), ce->guc_id.id) ||
 		!intel_context_is_pinned(ce);
-- 
2.51.1