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). This started in commit 3d3d18f086cdda72ee18a454db70ca72c6e3246c and lockdep didn't detect it apparently. 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 Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> --- drivers/gpu/drm/i915/i915_gem.c | 9 +++++++++ drivers/gpu/drm/i915/i915_gem_shrinker.c | 14 ++++++++++---- 2 files changed, 19 insertions(+), 4 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 67b1fc5..3982489 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -4742,6 +4742,13 @@ int i915_gem_freeze(struct drm_i915_private *dev_priv) i915_gem_shrink_all(dev_priv); mutex_unlock(&dev_priv->drm.struct_mutex); + /* + * Cannot call synchronize_rcu() inside the struct_mutex + * because it may block until workqueues complete, and the + * running workqueue may wait on the struct_mutex. + */ + synchronize_rcu(); /* wait for our earlier RCU delayed slab frees */ + intel_runtime_pm_put(dev_priv); return 0; @@ -4781,6 +4788,8 @@ int i915_gem_freeze_late(struct drm_i915_private *dev_priv) } mutex_unlock(&dev_priv->drm.struct_mutex); + synchronize_rcu_expedited(); + return 0; } diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c index d5d2b4c..fea1454 100644 --- a/drivers/gpu/drm/i915/i915_gem_shrinker.c +++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c @@ -235,9 +235,6 @@ i915_gem_shrink(struct drm_i915_private *dev_priv, if (unlock) mutex_unlock(&dev_priv->drm.struct_mutex); - /* expedite the RCU grace period to free some request slabs */ - synchronize_rcu_expedited(); - return count; } @@ -263,7 +260,6 @@ unsigned long i915_gem_shrink_all(struct drm_i915_private *dev_priv) I915_SHRINK_BOUND | I915_SHRINK_UNBOUND | I915_SHRINK_ACTIVE); - synchronize_rcu(); /* wait for our earlier RCU delayed slab frees */ return freed; } @@ -324,6 +320,16 @@ i915_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc) if (unlock) mutex_unlock(&dev->struct_mutex); + if (likely(__mutex_owner(&dev->struct_mutex) != current)) + /* + * If reclaim was invoked by an allocation done while + * holding the struct mutex, we cannot call + * synchronize_rcu_expedited() as it depends on + * workqueues to run but the running workqueue may be + * blocked waiting on us to release struct_mutex. + */ + synchronize_rcu_expedited(); + return freed; } _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
