[PATCH v9 2/2] drm/i915/guc: Close deregister-context race against CT-loss
Alan Previn
alan.previn.teres.alexis at intel.com
Thu Dec 28 04:55:58 UTC 2023
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 <alan.previn.teres.alexis at intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta at intel.com>
Tested-by: Mousumi Jana <mousumi.jana at intel.com>
Acked-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>
---
drivers/gpu/drm/i915/gem/i915_gem_pm.c | 10 +++
.../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);
}
--
2.39.0
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