On Fri, Apr 10, 2020 at 07:17:38AM -0700, Sultan Alsawaf wrote:
On Fri, Apr 10, 2020 at 11:08:38AM +0200, Greg KH wrote:
On Tue, Apr 07, 2020 at 12:18:09AM -0700, Sultan Alsawaf wrote:
From: Sultan Alsawaf sultan@kerneltoast.com
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@vger.kernel.org # 5.4.x Signed-off-by: Sultan Alsawaf sultan@kerneltoast.com
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
I'm sorry, I meant the v3 [1]. Apologies for the confusion. The v3 was picked into Ubuntu so that's what we're rolling with.
Ok, thanks, hopefully now I picked upthe right one...
greg k-h