This is a note to let you know that I've just added the patch titled drm/i915: Fix ref->mutex deadlock in i915_active_wait() to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: drm-i915-fix-ref-mutex-deadlock-in-i915_active_wait.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From sultan@xxxxxxxxxxxxxxx Sat Apr 11 13:39:11 2020 From: Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx> Date: Tue, 7 Apr 2020 13:32:22 -0700 Subject: drm/i915: Fix ref->mutex deadlock in i915_active_wait() To: stable@xxxxxxxxxxxxxxx Cc: Greg KH <greg@xxxxxxxxx>, Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>, Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>, Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>, David Airlie <airlied@xxxxxxxx>, Daniel Vetter <daniel@xxxxxxxx>, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>, intel-gfx@xxxxxxxxxxxxxxxxxxxxx, dri-devel@xxxxxxxxxxxxxxxxxxxxx, Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx> Message-ID: <20200407203222.2493-1-sultan@xxxxxxxxxxxxxxx> From: Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx> The following deadlock exists in i915_active_wait() due to a double lock on ref->mutex (call chain listed in order from top to bottom): i915_active_wait(); mutex_lock_interruptible(&ref->mutex); <-- ref->mutex first acquired i915_active_request_retire(); node_retire(); active_retire(); mutex_lock_nested(&ref->mutex, SINGLE_DEPTH_NESTING); <-- DEADLOCK Fix the deadlock by skipping the second ref->mutex lock when active_retire() is called through i915_active_request_retire(). Note that this bug only affects 5.4 and has since been fixed in 5.5. Normally, a backport of the fix from 5.5 would be in order, but the patch set that fixes this deadlock involves massive changes that are neither feasible nor desirable for backporting [1][2][3]. Therefore, this small patch was made to address the deadlock specifically for 5.4. [1] 274cbf20fd10 ("drm/i915: Push the i915_active.retire into a worker") [2] 093b92287363 ("drm/i915: Split i915_active.mutex into an irq-safe spinlock for the rbtree") [3] 750bde2fd4ff ("drm/i915: Serialise with remote retirement") Fixes: 12c255b5dad1 ("drm/i915: Provide an i915_active.acquire callback") Cc: <stable@xxxxxxxxxxxxxxx> # 5.4.x Signed-off-by: Sultan Alsawaf <sultan@xxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/gpu/drm/i915/i915_active.c | 29 +++++++++++++++++++---------- drivers/gpu/drm/i915/i915_active.h | 4 ++-- 2 files changed, 21 insertions(+), 12 deletions(-) --- a/drivers/gpu/drm/i915/i915_active.c +++ b/drivers/gpu/drm/i915/i915_active.c @@ -121,7 +121,7 @@ static inline void debug_active_assert(s #endif static void -__active_retire(struct i915_active *ref) +__active_retire(struct i915_active *ref, bool lock) { struct active_node *it, *n; struct rb_root root; @@ -138,7 +138,8 @@ __active_retire(struct i915_active *ref) retire = true; } - mutex_unlock(&ref->mutex); + if (likely(lock)) + mutex_unlock(&ref->mutex); if (!retire) return; @@ -153,21 +154,28 @@ __active_retire(struct i915_active *ref) } static void -active_retire(struct i915_active *ref) +active_retire(struct i915_active *ref, bool lock) { GEM_BUG_ON(!atomic_read(&ref->count)); if (atomic_add_unless(&ref->count, -1, 1)) return; /* One active may be flushed from inside the acquire of another */ - mutex_lock_nested(&ref->mutex, SINGLE_DEPTH_NESTING); - __active_retire(ref); + if (likely(lock)) + mutex_lock_nested(&ref->mutex, SINGLE_DEPTH_NESTING); + __active_retire(ref, lock); } static void node_retire(struct i915_active_request *base, struct i915_request *rq) { - active_retire(node_from_active(base)->ref); + active_retire(node_from_active(base)->ref, true); +} + +static void +node_retire_nolock(struct i915_active_request *base, struct i915_request *rq) +{ + active_retire(node_from_active(base)->ref, false); } static struct i915_active_request * @@ -364,7 +372,7 @@ int i915_active_acquire(struct i915_acti void i915_active_release(struct i915_active *ref) { debug_active_assert(ref); - active_retire(ref); + active_retire(ref, true); } static void __active_ungrab(struct i915_active *ref) @@ -391,7 +399,7 @@ void i915_active_ungrab(struct i915_acti { GEM_BUG_ON(!test_bit(I915_ACTIVE_GRAB_BIT, &ref->flags)); - active_retire(ref); + active_retire(ref, true); __active_ungrab(ref); } @@ -421,12 +429,13 @@ int i915_active_wait(struct i915_active break; } - err = i915_active_request_retire(&it->base, BKL(ref)); + err = i915_active_request_retire(&it->base, BKL(ref), + node_retire_nolock); if (err) break; } - __active_retire(ref); + __active_retire(ref, true); if (err) return err; --- a/drivers/gpu/drm/i915/i915_active.h +++ b/drivers/gpu/drm/i915/i915_active.h @@ -309,7 +309,7 @@ i915_active_request_isset(const struct i */ static inline int __must_check i915_active_request_retire(struct i915_active_request *active, - struct mutex *mutex) + struct mutex *mutex, i915_active_retire_fn retire) { struct i915_request *request; long ret; @@ -327,7 +327,7 @@ i915_active_request_retire(struct i915_a list_del_init(&active->link); RCU_INIT_POINTER(active->request, NULL); - active->retire(active, request); + retire(active, request); return 0; } Patches currently in stable-queue which might be from sultan@xxxxxxxxxxxxxxx are queue-5.4/drm-i915-fix-ref-mutex-deadlock-in-i915_active_wait.patch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx