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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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1
drivers/base/Kconfig
View File

@ -244,6 +244,7 @@ config DMA_SHARED_BUFFER
bool
default n
select ANON_INODES
select IRQ_WORK
help
This option enables the framework for buffer-sharing between
multiple drivers. A buffer is associated with a file using driver

14
drivers/dma-buf/dma-fence-array.c
View File

@ -31,6 +31,14 @@ static const char *dma_fence_array_get_timeline_name(struct dma_fence *fence)
return "unbound";
}
static void irq_dma_fence_array_work(struct irq_work *wrk)
{
struct dma_fence_array *array = container_of(wrk, typeof(*array), work);
dma_fence_signal(&array->base);
dma_fence_put(&array->base);
}
static void dma_fence_array_cb_func(struct dma_fence *f,
struct dma_fence_cb *cb)
{
@ -39,8 +47,9 @@ static void dma_fence_array_cb_func(struct dma_fence *f,
struct dma_fence_array *array = array_cb->array;
if (atomic_dec_and_test(&array->num_pending))
dma_fence_signal(&array->base);
dma_fence_put(&array->base);
irq_work_queue(&array->work);
else
dma_fence_put(&array->base);
}
static bool dma_fence_array_enable_signaling(struct dma_fence *fence)
@ -136,6 +145,7 @@ struct dma_fence_array *dma_fence_array_create(int num_fences,
spin_lock_init(&array->lock);
dma_fence_init(&array->base, &dma_fence_array_ops, &array->lock,
context, seqno);
init_irq_work(&array->work, irq_dma_fence_array_work);
array->num_fences = num_fences;
atomic_set(&array->num_pending, signal_on_any ? 1 : num_fences);

3
include/linux/dma-fence-array.h
View File

@ -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;