[PATCH 2/2] drm/i915/guc: Don't unblock a banned 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_banned(), which stays set. 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 (AI coding assistant); 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>
---
 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 555ca8f..eb1d010 100644
--- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
+++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
@@ -3182,7 +3182,12 @@ 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.
+	 */
 	return (ce->guc_state.sched_state & SCHED_STATE_NO_UNBLOCK) ||
+		intel_context_is_banned(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