On Tue, Apr 07, 2020 at 12:18:09AM -0700, Sultan Alsawaf wrote: > 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> > --- > drivers/gpu/drm/i915/i915_active.c | 27 +++++++++++++++++++++++---- > drivers/gpu/drm/i915/i915_active.h | 4 ++-- > 2 files changed, 25 insertions(+), 6 deletions(-) Now queued up, thanks. greg k-h _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel