[PATCH 4/8] sync_file: add a mutex to protect fence and callback members. (v4)
Christian König
deathsimple at vodafone.de
Tue Apr 4 08:07:36 UTC 2017
Am 04.04.2017 um 06:27 schrieb Dave Airlie:
> From: Dave Airlie <airlied at redhat.com>
>
> This patch allows the underlying fence in a sync_file to be changed
> or set to NULL. This isn't currently required but for Vulkan
> semaphores we need to be able to swap and reset the fence.
>
> In order to faciliate this, it uses rcu to protect the fence,
> along with a new mutex. The mutex also protects the callback.
> It also checks for NULL when retrieving the rcu protected
> fence in case it has been reset.
>
> v1.1: fix the locking (Julia Lawall).
> v2: use rcu try one
> v3: fix poll to use proper rcu, fixup merge/fill ioctls
> to not crash on NULL fence cases.
> v4: use rcu in even more places, add missing fput
>
> Signed-off-by: Dave Airlie <airlied at redhat.com>
> ---
> drivers/dma-buf/sync_file.c | 135 +++++++++++++++++++++++++++++++++++---------
> include/linux/sync_file.h | 6 +-
> 2 files changed, 112 insertions(+), 29 deletions(-)
>
> diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
> index 153bf03..6376f6f 100644
> --- a/drivers/dma-buf/sync_file.c
> +++ b/drivers/dma-buf/sync_file.c
> @@ -28,6 +28,10 @@
>
> static const struct file_operations sync_file_fops;
>
> +#define sync_file_held(obj) lockdep_is_held(&(obj)->lock)
> +#define sync_file_assert_held(obj) \
> + lockdep_assert_held(&(obj)->lock)
> +
> /**
> * sync_file_validate_type_flags - validate type/flags for support
> * @type: type of sync file object
> @@ -81,6 +85,10 @@ struct sync_file *sync_file_alloc(uint32_t type, uint32_t flags)
>
> sync_file->type = type;
> sync_file->flags = flags;
> +
> + RCU_INIT_POINTER(sync_file->fence, NULL);
> +
> + mutex_init(&sync_file->lock);
> return sync_file;
>
> err:
> @@ -117,7 +125,9 @@ struct sync_file *sync_file_create(struct dma_fence *fence,
> if (!sync_file)
> return NULL;
>
> - sync_file->fence = dma_fence_get(fence);
> + dma_fence_get(fence);
> +
> + RCU_INIT_POINTER(sync_file->fence, fence);
>
> snprintf(sync_file->name, sizeof(sync_file->name), "%s-%s%llu-%d",
> fence->ops->get_driver_name(fence),
> @@ -168,13 +178,28 @@ struct dma_fence *sync_file_get_fence(int fd)
> if (!sync_file)
> return NULL;
>
> - fence = dma_fence_get(sync_file->fence);
> + if (!rcu_access_pointer(sync_file->fence)) {
> + fput(sync_file->file);
> + return NULL;
> + }
> +
> + rcu_read_lock();
> + fence = dma_fence_get_rcu_safe(&sync_file->fence);
> + rcu_read_unlock();
> +
> fput(sync_file->file);
>
> return fence;
> }
> EXPORT_SYMBOL(sync_file_get_fence);
>
> +static inline struct dma_fence *
> +sync_file_get_fence_locked(struct sync_file *sync_file)
> +{
> + return rcu_dereference_protected(sync_file->fence,
> + sync_file_held(sync_file));
> +}
> +
> static int sync_file_set_fence(struct sync_file *sync_file,
> struct dma_fence **fences, int num_fences)
> {
> @@ -187,7 +212,7 @@ static int sync_file_set_fence(struct sync_file *sync_file,
> * we own the reference of the dma_fence_array creation.
> */
> if (num_fences == 1) {
> - sync_file->fence = fences[0];
> + RCU_INIT_POINTER(sync_file->fence, fences[0]);
> kfree(fences);
> } else {
> array = dma_fence_array_create(num_fences, fences,
> @@ -196,24 +221,30 @@ static int sync_file_set_fence(struct sync_file *sync_file,
> if (!array)
> return -ENOMEM;
>
> - sync_file->fence = &array->base;
> + RCU_INIT_POINTER(sync_file->fence, &array->base);
> }
>
> return 0;
> }
>
> -static struct dma_fence **get_fences(struct sync_file *sync_file,
> +/* must be called with rcu read lock taken */
> +static struct dma_fence **get_fences(struct dma_fence **fence,
> int *num_fences)
> {
> - if (dma_fence_is_array(sync_file->fence)) {
> - struct dma_fence_array *array = to_dma_fence_array(sync_file->fence);
> + if (!*fence) {
> + *num_fences = 0;
> + return NULL;
> + }
> +
> + if (dma_fence_is_array(*fence)) {
> + struct dma_fence_array *array = to_dma_fence_array(*fence);
>
> *num_fences = array->num_fences;
> return array->fences;
> }
>
> *num_fences = 1;
> - return &sync_file->fence;
> + return fence;
> }
>
> static void add_fence(struct dma_fence **fences,
> @@ -243,18 +274,31 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
> struct sync_file *sync_file;
> struct dma_fence **fences, **nfences, **a_fences, **b_fences;
> int i, i_a, i_b, num_fences, a_num_fences, b_num_fences;
> + struct dma_fence *a_fence, *b_fence;
>
> if (a->type != b->type)
> return NULL;
>
> - sync_file = sync_file_alloc(a->type, a->flags);
> - if (!sync_file)
> + if (!rcu_access_pointer(a->fence) ||
> + !rcu_access_pointer(b->fence))
> return NULL;
>
> - a_fences = get_fences(a, &a_num_fences);
> - b_fences = get_fences(b, &b_num_fences);
> + rcu_read_lock();
> + a_fence = dma_fence_get_rcu_safe(&a->fence);
> + b_fence = dma_fence_get_rcu_safe(&b->fence);
> + rcu_read_unlock();
> +
> + a_fences = get_fences(&a_fence, &a_num_fences);
> + b_fences = get_fences(&b_fence, &b_num_fences);
> + if (!a_num_fences || !b_num_fences)
> + goto put_src_fences;
> +
> if (a_num_fences > INT_MAX - b_num_fences)
> - return NULL;
> + goto put_src_fences;
> +
> + sync_file = sync_file_alloc(a->type, a->flags);
> + if (!sync_file)
> + goto put_src_fences;
>
> num_fences = a_num_fences + b_num_fences;
>
> @@ -315,11 +359,16 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
> goto err;
> }
>
> + dma_fence_put(a_fence);
> + dma_fence_put(b_fence);
> strlcpy(sync_file->name, name, sizeof(sync_file->name));
> return sync_file;
>
> err:
> fput(sync_file->file);
> +put_src_fences:
> + dma_fence_put(a_fence);
> + dma_fence_put(b_fence);
> return NULL;
>
> }
> @@ -328,10 +377,15 @@ static void sync_file_free(struct kref *kref)
> {
> struct sync_file *sync_file = container_of(kref, struct sync_file,
> kref);
> + struct dma_fence *fence;
> +
> + fence = rcu_dereference_protected(sync_file->fence, 1);
> + if (fence) {
> + if (test_bit(POLL_ENABLED, &fence->flags))
> + dma_fence_remove_callback(fence, &sync_file->cb);
> + dma_fence_put(fence);
> + }
>
> - if (test_bit(POLL_ENABLED, &sync_file->fence->flags))
> - dma_fence_remove_callback(sync_file->fence, &sync_file->cb);
> - dma_fence_put(sync_file->fence);
> kfree(sync_file);
> }
>
> @@ -346,16 +400,25 @@ static int sync_file_release(struct inode *inode, struct file *file)
> static unsigned int sync_file_poll(struct file *file, poll_table *wait)
> {
> struct sync_file *sync_file = file->private_data;
> + unsigned int ret_val = 0;
> + struct dma_fence *fence;
>
> poll_wait(file, &sync_file->wq, wait);
>
> - if (!test_and_set_bit(POLL_ENABLED, &sync_file->fence->flags)) {
> - if (dma_fence_add_callback(sync_file->fence, &sync_file->cb,
> - fence_check_cb_func) < 0)
> - wake_up_all(&sync_file->wq);
> + mutex_lock(&sync_file->lock);
> +
> + fence = sync_file_get_fence_locked(sync_file);
> + if (fence) {
> + if (!test_and_set_bit(POLL_ENABLED, &fence->flags)) {
> + if (dma_fence_add_callback(fence, &sync_file->cb,
> + fence_check_cb_func) < 0)
> + wake_up_all(&sync_file->wq);
> + }
> + ret_val = dma_fence_is_signaled(fence) ? POLLIN : 0;
> }
> + mutex_unlock(&sync_file->lock);
Maybe I'm a bit confused, but why exactly are you taking the lock here?
It isn't protecting anything anymore as far as I can see.
Or is it to prevent concurrent adding of the same callback? That would
have failed before if I'm not completely mistaken.
Christian.
>
> - return dma_fence_is_signaled(sync_file->fence) ? POLLIN : 0;
> + return ret_val;
> }
>
> static long sync_file_ioctl_merge(struct sync_file *sync_file,
> @@ -431,6 +494,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
> struct sync_file_info info;
> struct sync_fence_info *fence_info = NULL;
> struct dma_fence **fences;
> + struct dma_fence *fence;
> __u32 size;
> int num_fences, ret, i;
>
> @@ -440,7 +504,15 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
> if (info.flags || info.pad)
> return -EINVAL;
>
> - fences = get_fences(sync_file, &num_fences);
> + rcu_read_lock();
> + fence = dma_fence_get_rcu_safe(&sync_file->fence);
> + rcu_read_unlock();
> +
> + fences = get_fences(&fence, &num_fences);
> +
> + /* if there are no fences in the sync_file just return */
> + if (!num_fences)
> + goto no_fences;
>
> /*
> * Passing num_fences = 0 means that userspace doesn't want to
> @@ -451,13 +523,17 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
> if (!info.num_fences)
> goto no_fences;
>
> - if (info.num_fences < num_fences)
> - return -EINVAL;
> + if (info.num_fences < num_fences) {
> + ret = -EINVAL;
> + goto out;
> + }
>
> size = num_fences * sizeof(*fence_info);
> fence_info = kzalloc(size, GFP_KERNEL);
> - if (!fence_info)
> - return -ENOMEM;
> + if (!fence_info) {
> + ret = -ENOMEM;
> + goto out;
> + }
>
> for (i = 0; i < num_fences; i++)
> sync_fill_fence_info(fences[i], &fence_info[i]);
> @@ -470,7 +546,10 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
>
> no_fences:
> strlcpy(info.name, sync_file->name, sizeof(info.name));
> - info.status = dma_fence_is_signaled(sync_file->fence);
> + if (num_fences)
> + info.status = dma_fence_is_signaled(sync_file->fence);
> + else
> + info.status = -ENOENT;
> info.num_fences = num_fences;
>
> if (copy_to_user((void __user *)arg, &info, sizeof(info)))
> @@ -480,7 +559,7 @@ static long sync_file_ioctl_fence_info(struct sync_file *sync_file,
>
> out:
> kfree(fence_info);
> -
> + dma_fence_put(fence);
> return ret;
> }
>
> diff --git a/include/linux/sync_file.h b/include/linux/sync_file.h
> index e683dd1..4bf661b 100644
> --- a/include/linux/sync_file.h
> +++ b/include/linux/sync_file.h
> @@ -34,6 +34,7 @@
> * @cb: fence callback information
> * @type: sync file type
> * @flags: flags used to create sync file
> + * @lock: mutex to protect fence/cb - used for semaphores
> */
> struct sync_file {
> struct file *file;
> @@ -45,10 +46,13 @@ struct sync_file {
>
> wait_queue_head_t wq;
>
> - struct dma_fence *fence;
> + struct dma_fence __rcu *fence;
> struct dma_fence_cb cb;
> uint32_t type;
> uint32_t flags;
> +
> + /* protects the fence pointer and cb */
> + struct mutex lock;
> };
>
> #define POLL_ENABLED DMA_FENCE_FLAG_USER_BITS
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