On Mon, Aug 14, 2023 at 06:12:09PM -0700, Alan Previn wrote:
> If we are at the end of suspend or very early in resume
> its possible an async fence signal could lead us to the
> execution of the context destruction worker (after the
> prior worker flush).
>
> Even if checking that the CT is enabled before calling
> destroyed_worker_func, guc_lrc_desc_unpin may still fail
> because in corner cases, as we traverse the GuC's
> context-destroy list, the CT could get disabled in the mid
> of it right before calling the 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 unpin 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. That 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
>
> Doing this unroll and keeping the context in the GuC's
> destroy-list will allow the context to get picked up on
> the next destroy worker invocation or purged as part of a
> major GuC sanitization or reset flow.
>
> Signed-off-by: Alan Previn <alan.previn.teres.alexis@xxxxxxxxx>
> ---
> .../gpu/drm/i915/gt/uc/intel_guc_submission.c | 40 +++++++++++++++++--
> 1 file changed, 36 insertions(+), 4 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 050572bb8dbe..ddb4ee4c4e51 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -235,6 +235,13 @@ 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;
> @@ -3175,7 +3182,7 @@ 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);
> @@ -3199,10 +3206,20 @@ static inline void guc_lrc_desc_unpin(struct intel_context *ce)
> if (unlikely(disabled)) {
> release_guc_id(guc, ce);
> __guc_context_destroy(ce);
> - return;
> + return 0;
> + }
> +
> + if (deregister_context(ce, ce->guc_id.id)) {
> + /* Seal race with concurrent suspend by unrolling */
> + spin_lock_irqsave(&ce->guc_state.lock, flags);
> + set_context_registered(ce);
> + clr_context_destroyed(ce);
> + intel_gt_pm_put(gt);
how sure we are this is not calling unbalanced puts?
could we wrap this in some existent function to make this clear?
> + spin_unlock_irqrestore(&ce->guc_state.lock, flags);
> + return -ENODEV;
> }
>
> - deregister_context(ce, ce->guc_id.id);
> + return 0;
> }
>
> static void __guc_context_destroy(struct intel_context *ce)
> @@ -3270,7 +3287,22 @@ 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;
> + }
> +
> }
> }
>
> --
> 2.39.0
>
