[PATCH 4.15 033/128] dma-buf/fence: Fix lock inversion within dma-fence-array

Greg Kroah-Hartman
2018-03-16T15:22:54Z

From: Chris Wilson <chris@chris-wilson.co.uk>

[ 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>
---
drivers/base/Kconfig | 1 +
drivers/dma-buf/dma-fence-array.c | 14 ++++++++++++--
include/linux/dma-fence-array.h | 3 +++
3 files changed, 16 insertions(+), 2 deletions(-)

--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -249,6 +249,7 @@ 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
--- a/drivers/dma-buf/dma-fence-array.c
+++ b/drivers/dma-buf/dma-fence-array.c
@@ -31,6 +31,14 @@ static const char *dma_fence_array_get_t
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(stru
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_
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);
--- a/include/linux/dma-fence-array.h
+++ b/include/linux/dma-fence-array.h
@@ -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;