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dma-buf/fence: Fix lock inversion within dma-fence-array

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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
This commit is contained in:
Chris Wilson
2017-11-14 16:27:19 +00:00
committed by Sumit Semwal
parent 70c5f93669
commit 03e4e0a9e0
3 changed files with 16 additions and 2 deletions
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3
include/linux/dma-fence-array.h
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@@ -21,6 +21,7 @@
#define __LINUX_DMA_FENCE_ARRAY_H
#include <linux/dma-fence.h>
#include <linux/irq_work.h>
/**
* struct dma_fence_array_cb - callback helper for fence array
@@ -47,6 +48,8 @@ struct dma_fence_array {
unsigned num_fences;
atomic_t num_pending;
struct dma_fence **fences;
struct irq_work work;
};
extern const struct dma_fence_ops dma_fence_array_ops;