If we attempt to wake up a waiter, who is currently checking the seqno it will be in the TASK_INTERRUPTIBLE state and ttwu will report success. However, it is actually awake and functioning -- so delay reporting the actual wake up until it sleeps.
v2: Defend against !CONFIG_SMP References: https://bugs.freedesktop.org/show_bug.cgi?id=100007 Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk> Cc: Tvrtko Ursulin <tvrtko.ursu...@intel.com> Cc: Joonas Lahtinen <joonas.lahti...@linux.intel.com> --- drivers/gpu/drm/i915/intel_breadcrumbs.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c index 9ccbf26124c6..4fdf7868e2f1 100644 --- a/drivers/gpu/drm/i915/intel_breadcrumbs.c +++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c @@ -27,6 +27,23 @@ #include "i915_drv.h" +#ifdef CONFIG_SMP +#define task_asleep(tsk) (!(tsk)->on_cpu) +#else +#define task_asleep(tsk) ((tsk) != current) +#endif + +static inline bool __wake_up_sleeper(struct task_struct *tsk) +{ + /* Be careful not to report a successful wakeup if the waiter is + * currently processing the seqno, where it will have already + * called set_task_state(TASK_INTERRUPTIBLE). We first check whether + * the task is currently asleep before calling ttwu, and then we + * only report success if we were the ones to then trigger the wakeup. + */ + return task_asleep(tsk) && wake_up_process(tsk); +} + static unsigned int __intel_breadcrumbs_wakeup(struct intel_breadcrumbs *b) { struct intel_wait *wait; @@ -37,7 +54,7 @@ static unsigned int __intel_breadcrumbs_wakeup(struct intel_breadcrumbs *b) wait = b->irq_wait; if (wait) { result = ENGINE_WAKEUP_WAITER; - if (wake_up_process(wait->tsk)) + if (__wake_up_sleeper(wait->tsk)) result |= ENGINE_WAKEUP_ASLEEP; } @@ -198,7 +215,7 @@ void intel_engine_disarm_breadcrumbs(struct intel_engine_cs *engine) rbtree_postorder_for_each_entry_safe(wait, n, &b->waiters, node) { RB_CLEAR_NODE(&wait->node); - if (wake_up_process(wait->tsk) && wait == first) + if (__wake_up_sleeper(wait->tsk) && wait == first) missed_breadcrumb(engine); } b->waiters = RB_ROOT; -- 2.11.0 _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
