From 2f2cc53b5fe7022f3ae602eb24573d52f8740959 Mon Sep 17 00:00:00 2001 From: Alan Previn Date: Fri, 29 Dec 2023 13:51:43 -0800 Subject: drm/i915/guc: Close deregister-context race against CT-loss If we are at the end of suspend or very early in resume its possible an async fence signal (via rcu_call) is triggered to free_engines which could lead us to the execution of the context destruction worker (after a prior worker flush). Thus, when suspending, insert rcu_barriers at the start of i915_gem_suspend (part of driver's suspend prepare) and again in i915_gem_suspend_late so that all such cases have completed and context destruction list isn't missing anything. In destroyed_worker_func, close the race against CT-loss by checking that CT is enabled before calling into deregister_destroyed_contexts. Based on testing, guc_lrc_desc_unpin may still race and fail as we traverse the GuC's context-destroy list because the CT could be disabled right before calling GuC's CT send function. We've witnessed this race condition once every ~6000-8000 suspend-resume cycles while ensuring workloads that render something onscreen is continuously started just before we suspend (and the workload is small enough to complete and trigger the queued engine/context free-up either very late in suspend or very early in resume). In such a case, we need to unroll the entire process because guc-lrc-unpin takes a gt wakeref which only gets released in the G2H IRQ reply that never comes through in this corner case. Without the unroll, the taken wakeref is leaked and will cascade into a kernel hang later at the tail end of suspend in this function: intel_wakeref_wait_for_idle(>->wakeref) (called by) - intel_gt_pm_wait_for_idle (called by) - wait_for_suspend Thus, do an unroll in guc_lrc_desc_unpin and deregister_destroyed_- contexts if guc_lrc_desc_unpin fails due to CT send falure. When unrolling, keep the context in the GuC's destroy-list so it can get picked up on the next destroy worker invocation (if suspend aborted) or get fully purged as part of a GuC sanitization (end of suspend) or a reset flow. Signed-off-by: Alan Previn Signed-off-by: Anshuman Gupta Tested-by: Mousumi Jana Acked-by: Daniele Ceraolo Spurio Reviewed-by: Rodrigo Vivi Signed-off-by: Matt Roper Link: https://patchwork.freedesktop.org/patch/msgid/20231229215143.581619-1-alan.previn.teres.alexis@intel.com --- drivers/gpu/drm/i915/gem/i915_gem_pm.c | 10 ++++ drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 73 +++++++++++++++++++++-- 2 files changed, 78 insertions(+), 5 deletions(-) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pm.c b/drivers/gpu/drm/i915/gem/i915_gem_pm.c index 0d812f4d787d..3b27218aabe2 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_pm.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_pm.c @@ -28,6 +28,13 @@ void i915_gem_suspend(struct drm_i915_private *i915) GEM_TRACE("%s\n", dev_name(i915->drm.dev)); intel_wakeref_auto(&i915->runtime_pm.userfault_wakeref, 0); + /* + * On rare occasions, we've observed the fence completion triggers + * free_engines asynchronously via rcu_call. Ensure those are done. + * This path is only called on suspend, so it's an acceptable cost. + */ + rcu_barrier(); + flush_workqueue(i915->wq); /* @@ -160,6 +167,9 @@ void i915_gem_suspend_late(struct drm_i915_private *i915) * machine in an unusable condition. */ + /* Like i915_gem_suspend, flush tasks staged from fence triggers */ + rcu_barrier(); + for_each_gt(gt, i915, i) intel_gt_suspend_late(gt); 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 9c64ae0766cc..cae637fc3ead 100644 --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c @@ -236,6 +236,13 @@ set_context_destroyed(struct intel_context *ce) ce->guc_state.sched_state |= SCHED_STATE_DESTROYED; } +static inline void +clr_context_destroyed(struct intel_context *ce) +{ + lockdep_assert_held(&ce->guc_state.lock); + ce->guc_state.sched_state &= ~SCHED_STATE_DESTROYED; +} + static inline bool context_pending_disable(struct intel_context *ce) { return ce->guc_state.sched_state & SCHED_STATE_PENDING_DISABLE; @@ -613,6 +620,8 @@ static int guc_submission_send_busy_loop(struct intel_guc *guc, u32 g2h_len_dw, bool loop) { + int ret; + /* * We always loop when a send requires a reply (i.e. g2h_len_dw > 0), * so we don't handle the case where we don't get a reply because we @@ -623,7 +632,11 @@ static int guc_submission_send_busy_loop(struct intel_guc *guc, if (g2h_len_dw) atomic_inc(&guc->outstanding_submission_g2h); - return intel_guc_send_busy_loop(guc, action, len, g2h_len_dw, loop); + ret = intel_guc_send_busy_loop(guc, action, len, g2h_len_dw, loop); + if (ret) + atomic_dec(&guc->outstanding_submission_g2h); + + return ret; } int intel_guc_wait_for_pending_msg(struct intel_guc *guc, @@ -3288,12 +3301,13 @@ static void guc_context_close(struct intel_context *ce) spin_unlock_irqrestore(&ce->guc_state.lock, flags); } -static inline void guc_lrc_desc_unpin(struct intel_context *ce) +static inline int guc_lrc_desc_unpin(struct intel_context *ce) { struct intel_guc *guc = ce_to_guc(ce); struct intel_gt *gt = guc_to_gt(guc); unsigned long flags; bool disabled; + int ret; GEM_BUG_ON(!intel_gt_pm_is_awake(gt)); GEM_BUG_ON(!ctx_id_mapped(guc, ce->guc_id.id)); @@ -3304,18 +3318,41 @@ static inline void guc_lrc_desc_unpin(struct intel_context *ce) spin_lock_irqsave(&ce->guc_state.lock, flags); disabled = submission_disabled(guc); if (likely(!disabled)) { + /* + * Take a gt-pm ref and change context state to be destroyed. + * NOTE: a G2H IRQ that comes after will put this gt-pm ref back + */ __intel_gt_pm_get(gt); set_context_destroyed(ce); clr_context_registered(ce); } spin_unlock_irqrestore(&ce->guc_state.lock, flags); + if (unlikely(disabled)) { release_guc_id(guc, ce); __guc_context_destroy(ce); - return; + return 0; } - deregister_context(ce, ce->guc_id.id); + /* + * 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. + */ + ret = deregister_context(ce, ce->guc_id.id); + if (ret) { + spin_lock(&ce->guc_state.lock); + set_context_registered(ce); + clr_context_destroyed(ce); + spin_unlock(&ce->guc_state.lock); + /* + * 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); + } + + return ret; } static void __guc_context_destroy(struct intel_context *ce) @@ -3383,7 +3420,22 @@ static void deregister_destroyed_contexts(struct intel_guc *guc) if (!ce) break; - guc_lrc_desc_unpin(ce); + if (guc_lrc_desc_unpin(ce)) { + /* + * This means GuC's CT link severed mid-way which could happen + * in suspend-resume corner cases. In this case, put the + * context back into the destroyed_contexts list which will + * get picked up on the next context deregistration event or + * purged in a GuC sanitization event (reset/unload/wedged/...). + */ + spin_lock_irqsave(&guc->submission_state.lock, flags); + list_add_tail(&ce->destroyed_link, + &guc->submission_state.destroyed_contexts); + spin_unlock_irqrestore(&guc->submission_state.lock, flags); + /* Bail now since the list might never be emptied if h2gs fail */ + break; + } + } } @@ -3394,6 +3446,17 @@ static void destroyed_worker_func(struct work_struct *w) struct intel_gt *gt = guc_to_gt(guc); intel_wakeref_t wakeref; + /* + * In rare cases we can get here via async context-free fence-signals that + * come very late in suspend flow or very early in resume flows. In these + * cases, GuC won't be ready but just skipping it here is fine as these + * pending-destroy-contexts get destroyed totally at GuC reset time at the + * end of suspend.. OR.. this worker can be picked up later on the next + * context destruction trigger after resume-completes + */ + if (!intel_guc_is_ready(guc)) + return; + with_intel_gt_pm(gt, wakeref) deregister_destroyed_contexts(guc); } -- cgit