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linux-next/include/linux/dma-fence-array.h
Chris Wilson 03e4e0a9e0 dma-buf/fence: Fix lock inversion within dma-fence-array
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
2017-11-21 22:37:05 +05:30

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2.5 KiB
C

/*
* fence-array: aggregates fence to be waited together
*
* Copyright (C) 2016 Collabora Ltd
* Copyright (C) 2016 Advanced Micro Devices, Inc.
* Authors:
* Gustavo Padovan <gustavo@padovan.org>
* Christian König <christian.koenig@amd.com>
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 as published by
* the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
* more details.
*/
#ifndef __LINUX_DMA_FENCE_ARRAY_H
#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
* @cb: fence callback structure for signaling
* @array: reference to the parent fence array object
*/
struct dma_fence_array_cb {
struct dma_fence_cb cb;
struct dma_fence_array *array;
};
/**
* struct dma_fence_array - fence to represent an array of fences
* @base: fence base class
* @lock: spinlock for fence handling
* @num_fences: number of fences in the array
* @num_pending: fences in the array still pending
* @fences: array of the fences
*/
struct dma_fence_array {
struct dma_fence base;
spinlock_t lock;
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;
/**
* dma_fence_is_array - check if a fence is from the array subsclass
* @fence: fence to test
*
* Return true if it is a dma_fence_array and false otherwise.
*/
static inline bool dma_fence_is_array(struct dma_fence *fence)
{
return fence->ops == &dma_fence_array_ops;
}
/**
* to_dma_fence_array - cast a fence to a dma_fence_array
* @fence: fence to cast to a dma_fence_array
*
* Returns NULL if the fence is not a dma_fence_array,
* or the dma_fence_array otherwise.
*/
static inline struct dma_fence_array *
to_dma_fence_array(struct dma_fence *fence)
{
if (fence->ops != &dma_fence_array_ops)
return NULL;
return container_of(fence, struct dma_fence_array, base);
}
struct dma_fence_array *dma_fence_array_create(int num_fences,
struct dma_fence **fences,
u64 context, unsigned seqno,
bool signal_on_any);
bool dma_fence_match_context(struct dma_fence *fence, u64 context);
#endif /* __LINUX_DMA_FENCE_ARRAY_H */