From 0323a5127e7c534cfc88efe0f850a0cb777e938b Mon Sep 17 00:00:00 2001 From: Jesus Narvaez Date: Wed, 28 May 2025 16:05:51 -0700 Subject: [PATCH] drm/i915/guc: Handle race condition where wakeref count drops below 0 There is a rare race condition when preparing for a reset where guc_lrc_desc_unpin() could be in the process of deregistering a context while a different thread is scrubbing outstanding contexts and it alters the context state and does a wakeref put. Then, if there is a failure with deregister_context(), a second wakeref put could occur. As a result the wakeref count could drop below 0 and fail an INTEL_WAKEREF_BUG_ON() check. Therefore if there is a failure with deregister_context(), undo the context state changes and do a wakeref put only if the context was set to be destroyed earlier. v2: Expand comment to better explain change. (Daniele) v3: Removed addition to the original comment. (Daniele) Fixes: 2f2cc53b5fe7 ("drm/i915/guc: Close deregister-context race against CT-loss") Signed-off-by: Jesus Narvaez Cc: Daniele Ceraolo Spurio Cc: Alan Previn Cc: Anshuman Gupta Cc: Mousumi Jana Cc: Rodrigo Vivi Cc: Matt Roper Reviewed-by: Daniele Ceraolo Spurio Signed-off-by: John Harrison Link: https://lore.kernel.org/r/20250528230551.1855177-1-jesus.narvaez@intel.com (cherry picked from commit f36a75aba1c3176d177964bca76f86a075d2943a) Signed-off-by: Joonas Lahtinen --- .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) 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 108331a69995..127316d2c8aa 100644 --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c @@ -3443,18 +3443,29 @@ static inline int guc_lrc_desc_unpin(struct intel_context *ce) * GuC is active, lets destroy this context, but at this point we can still be racing * with suspend, so we undo everything if the H2G fails in deregister_context so * that GuC reset will find this context during clean up. + * + * There is a race condition where the reset code could have altered + * this context's state and done a wakeref put before we try to + * deregister it here. So check if the context is still set to be + * destroyed before undoing earlier changes, to avoid two wakeref puts + * on the same context. */ ret = deregister_context(ce, ce->guc_id.id); if (ret) { + bool pending_destroyed; spin_lock_irqsave(&ce->guc_state.lock, flags); - set_context_registered(ce); - clr_context_destroyed(ce); + pending_destroyed = context_destroyed(ce); + if (pending_destroyed) { + set_context_registered(ce); + clr_context_destroyed(ce); + } spin_unlock_irqrestore(&ce->guc_state.lock, flags); /* * As gt-pm is awake at function entry, intel_wakeref_put_async merely decrements * the wakeref immediately but per function spec usage call this after unlock. */ - intel_wakeref_put_async(>->wakeref); + if (pending_destroyed) + intel_wakeref_put_async(>->wakeref); } return ret; -- 2.25.1