linux/drivers/dma-buf/dma-fence-array.c
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

183 lines
5.4 KiB
C

/*
* dma-fence-array: aggregate fences 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.
*/
#include <linux/export.h>
#include <linux/slab.h>
#include <linux/dma-fence-array.h>
static const char *dma_fence_array_get_driver_name(struct dma_fence *fence)
{
return "dma_fence_array";
}
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)
{
struct dma_fence_array_cb *array_cb =
container_of(cb, struct dma_fence_array_cb, cb);
struct dma_fence_array *array = array_cb->array;
if (atomic_dec_and_test(&array->num_pending))
irq_work_queue(&array->work);
else
dma_fence_put(&array->base);
}
static bool dma_fence_array_enable_signaling(struct dma_fence *fence)
{
struct dma_fence_array *array = to_dma_fence_array(fence);
struct dma_fence_array_cb *cb = (void *)(&array[1]);
unsigned i;
for (i = 0; i < array->num_fences; ++i) {
cb[i].array = array;
/*
* As we may report that the fence is signaled before all
* callbacks are complete, we need to take an additional
* reference count on the array so that we do not free it too
* early. The core fence handling will only hold the reference
* until we signal the array as complete (but that is now
* insufficient).
*/
dma_fence_get(&array->base);
if (dma_fence_add_callback(array->fences[i], &cb[i].cb,
dma_fence_array_cb_func)) {
dma_fence_put(&array->base);
if (atomic_dec_and_test(&array->num_pending))
return false;
}
}
return true;
}
static bool dma_fence_array_signaled(struct dma_fence *fence)
{
struct dma_fence_array *array = to_dma_fence_array(fence);
return atomic_read(&array->num_pending) <= 0;
}
static void dma_fence_array_release(struct dma_fence *fence)
{
struct dma_fence_array *array = to_dma_fence_array(fence);
unsigned i;
for (i = 0; i < array->num_fences; ++i)
dma_fence_put(array->fences[i]);
kfree(array->fences);
dma_fence_free(fence);
}
const struct dma_fence_ops dma_fence_array_ops = {
.get_driver_name = dma_fence_array_get_driver_name,
.get_timeline_name = dma_fence_array_get_timeline_name,
.enable_signaling = dma_fence_array_enable_signaling,
.signaled = dma_fence_array_signaled,
.wait = dma_fence_default_wait,
.release = dma_fence_array_release,
};
EXPORT_SYMBOL(dma_fence_array_ops);
/**
* dma_fence_array_create - Create a custom fence array
* @num_fences: [in] number of fences to add in the array
* @fences: [in] array containing the fences
* @context: [in] fence context to use
* @seqno: [in] sequence number to use
* @signal_on_any: [in] signal on any fence in the array
*
* Allocate a dma_fence_array object and initialize the base fence with
* dma_fence_init().
* In case of error it returns NULL.
*
* The caller should allocate the fences array with num_fences size
* and fill it with the fences it wants to add to the object. Ownership of this
* array is taken and dma_fence_put() is used on each fence on release.
*
* If @signal_on_any is true the fence array signals if any fence in the array
* signals, otherwise it signals when all fences in the array signal.
*/
struct dma_fence_array *dma_fence_array_create(int num_fences,
struct dma_fence **fences,
u64 context, unsigned seqno,
bool signal_on_any)
{
struct dma_fence_array *array;
size_t size = sizeof(*array);
/* Allocate the callback structures behind the array. */
size += num_fences * sizeof(struct dma_fence_array_cb);
array = kzalloc(size, GFP_KERNEL);
if (!array)
return NULL;
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);
array->fences = fences;
return array;
}
EXPORT_SYMBOL(dma_fence_array_create);
/**
* dma_fence_match_context - Check if all fences are from the given context
* @fence: [in] fence or fence array
* @context: [in] fence context to check all fences against
*
* Checks the provided fence or, for a fence array, all fences in the array
* against the given context. Returns false if any fence is from a different
* context.
*/
bool dma_fence_match_context(struct dma_fence *fence, u64 context)
{
struct dma_fence_array *array = to_dma_fence_array(fence);
unsigned i;
if (!dma_fence_is_array(fence))
return fence->context == context;
for (i = 0; i < array->num_fences; i++) {
if (array->fences[i]->context != context)
return false;
}
return true;
}
EXPORT_SYMBOL(dma_fence_match_context);