From 8f612d055183545070ca1009ac2eb1f2e044cc20 Mon Sep 17 00:00:00 2001 From: Joonas Lahtinen Date: Fri, 7 Apr 2017 13:49:34 +0300 Subject: [PATCH] drm/i915: Don't call synchronize_rcu_expedited under struct_mutex Only call synchronize_rcu_expedited after unlocking struct_mutex to avoid deadlock because the workqueues depend on struct_mutex. >From original patch by Andrea: synchronize_rcu/synchronize_sched/synchronize_rcu_expedited() will hang until its own workqueues are run. The i915 gem workqueues will wait on the struct_mutex to be released. So we cannot wait for a quiescent state using those rcu primitives while holding the struct_mutex or it creates a circular lock dependency resulting in kernel hangs (which is reproducible but goes undetected by lockdep). kswapd0 D 0 700 2 0x00000000 Call Trace: ? __schedule+0x1a5/0x660 ? schedule+0x36/0x80 ? _synchronize_rcu_expedited.constprop.65+0x2ef/0x300 ? wake_up_bit+0x20/0x20 ? rcu_stall_kick_kthreads.part.54+0xc0/0xc0 ? rcu_exp_wait_wake+0x530/0x530 ? i915_gem_shrink+0x34b/0x4b0 ? i915_gem_shrinker_scan+0x7c/0x90 ? i915_gem_shrinker_scan+0x7c/0x90 ? shrink_slab.part.61.constprop.72+0x1c1/0x3a0 ? shrink_zone+0x154/0x160 ? kswapd+0x40a/0x720 ? kthread+0xf4/0x130 ? try_to_free_pages+0x450/0x450 ? kthread_create_on_node+0x40/0x40 ? ret_from_fork+0x23/0x30 plasmashell D 0 4657 4614 0x00000000 Call Trace: ? __schedule+0x1a5/0x660 ? schedule+0x36/0x80 ? schedule_preempt_disabled+0xe/0x10 ? __mutex_lock.isra.4+0x1c9/0x790 ? i915_gem_close_object+0x26/0xc0 ? i915_gem_close_object+0x26/0xc0 ? drm_gem_object_release_handle+0x48/0x90 ? drm_gem_handle_delete+0x50/0x80 ? drm_ioctl+0x1fa/0x420 ? drm_gem_handle_create+0x40/0x40 ? pipe_write+0x391/0x410 ? __vfs_write+0xc6/0x120 ? do_vfs_ioctl+0x8b/0x5d0 ? SyS_ioctl+0x3b/0x70 ? entry_SYSCALL_64_fastpath+0x13/0x94 kworker/0:0 D 0 29186 2 0x00000000 Workqueue: events __i915_gem_free_work Call Trace: ? __schedule+0x1a5/0x660 ? schedule+0x36/0x80 ? schedule_preempt_disabled+0xe/0x10 ? __mutex_lock.isra.4+0x1c9/0x790 ? del_timer_sync+0x44/0x50 ? update_curr+0x57/0x110 ? __i915_gem_free_objects+0x31/0x300 ? __i915_gem_free_objects+0x31/0x300 ? __i915_gem_free_work+0x2d/0x40 ? process_one_work+0x13a/0x3b0 ? worker_thread+0x4a/0x460 ? kthread+0xf4/0x130 ? process_one_work+0x3b0/0x3b0 ? kthread_create_on_node+0x40/0x40 ? ret_from_fork+0x23/0x30 Fixes: 3d3d18f086cd ("drm/i915: Avoid rcu_barrier() from reclaim paths (shrinker)") Reported-by: Andrea Arcangeli Signed-off-by: Joonas Lahtinen Cc: Andrea Arcangeli Cc: Chris Wilson Cc: Daniel Vetter Cc: Jani Nikula Reviewed-by: Chris Wilson --- drivers/gpu/drm/i915/i915_gem_shrinker.c | 26 +++++++++++++++--------- 1 file changed, 16 insertions(+), 10 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c index 2978acdd995e..129ed303a6c4 100644 --- a/drivers/gpu/drm/i915/i915_gem_shrinker.c +++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c @@ -53,6 +53,17 @@ static bool i915_gem_shrinker_lock(struct drm_device *dev, bool *unlock) BUG(); } +static void i915_gem_shrinker_unlock(struct drm_device *dev, bool unlock) +{ + if (!unlock) + return; + + mutex_unlock(&dev->struct_mutex); + + /* expedite the RCU grace period to free some request slabs */ + synchronize_rcu_expedited(); +} + static bool any_vma_pinned(struct drm_i915_gem_object *obj) { struct i915_vma *vma; @@ -232,11 +243,8 @@ i915_gem_shrink(struct drm_i915_private *dev_priv, intel_runtime_pm_put(dev_priv); i915_gem_retire_requests(dev_priv); - if (unlock) - mutex_unlock(&dev_priv->drm.struct_mutex); - /* expedite the RCU grace period to free some request slabs */ - synchronize_rcu_expedited(); + i915_gem_shrinker_unlock(&dev_priv->drm, unlock); return count; } @@ -296,8 +304,7 @@ i915_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc) count += obj->base.size >> PAGE_SHIFT; } - if (unlock) - mutex_unlock(&dev->struct_mutex); + i915_gem_shrinker_unlock(dev, unlock); return count; } @@ -324,8 +331,8 @@ i915_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc) sc->nr_to_scan - freed, I915_SHRINK_BOUND | I915_SHRINK_UNBOUND); - if (unlock) - mutex_unlock(&dev->struct_mutex); + + i915_gem_shrinker_unlock(dev, unlock); return freed; } @@ -367,8 +374,7 @@ i915_gem_shrinker_unlock_uninterruptible(struct drm_i915_private *dev_priv, struct shrinker_lock_uninterruptible *slu) { dev_priv->mm.interruptible = slu->was_interruptible; - if (slu->unlock) - mutex_unlock(&dev_priv->drm.struct_mutex); + i915_gem_shrinker_unlock(&dev_priv->drm, slu->unlock); } static int -- 2.20.1