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[ Upstream commit 03e4e0a9e02cf703da331ff6cfd57d0be9bf5692 ] Ages ago Rob Clark noted, "Currently with fence-array, we have a potential deadlock situation. If we fence_add_callback() on an array-fence, the array-fence's lock is acquired first, and in it's ->enable_signaling() callback, it will install cbs on it's array-member fences, so the array-member's lock is acquired second. But in the signal path, the array-member's lock is acquired first, and the array-fence's lock acquired second." Rob proposed either extensive changes to dma-fence to unnest the fence-array signaling, or to defer the signaling onto a workqueue. This is a more refined version of the later, that should keep the latency of the fence signaling to a minimum by using an irq-work, which is executed asap. Reported-by: Rob Clark <robdclark@gmail.com> Suggested-by: Rob Clark <robdclark@gmail.com> References: 1476635975-21981-1-git-send-email-robdclark@gmail.com Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Cc: Rob Clark <robdclark@gmail.com> Cc: Gustavo Padovan <gustavo.padovan@collabora.co.uk> Cc: Sumit Semwal <sumit.semwal@linaro.org> Cc: Christian König <christian.koenig@amd.com> Reviewed-by: Christian König <christian.koenig@amd.com> Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org> Link: https://patchwork.freedesktop.org/patch/msgid/20171114162719.30958-1-chris@chris-wilson.co.uk Signed-off-by: Sasha Levin <alexander.levin@microsoft.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>