Commit a517cca6 authored by Laurent Pinchart's avatar Laurent Pinchart Committed by Mauro Carvalho Chehab

[media] media: vb2: Fix potential deadlock in vb2_prepare_buffer

Commit b037c0fd ("media: vb2: fix
potential deadlock in mmap vs. get_userptr handling") fixes an AB-BA
deadlock related to the mmap_sem and driver locks. The same deadlock can
occur in vb2_prepare_buffer(), fix it the same way.
Signed-off-by: 's avatarLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: 's avatarHans Verkuil <hans.verkuil@cisco.com>
Acked-by: 's avatarMarek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: 's avatarMauro Carvalho Chehab <m.chehab@samsung.com>
parent 1ac7fdee
......@@ -1248,50 +1248,84 @@ static int __buf_prepare(struct vb2_buffer *vb, const struct v4l2_buffer *b)
*/
int vb2_prepare_buf(struct vb2_queue *q, struct v4l2_buffer *b)
{
struct rw_semaphore *mmap_sem = NULL;
struct vb2_buffer *vb;
int ret;
/*
* In case of user pointer buffers vb2 allocator needs to get direct
* access to userspace pages. This requires getting read access on
* mmap semaphore in the current process structure. The same
* semaphore is taken before calling mmap operation, while both mmap
* and prepare_buf are called by the driver or v4l2 core with driver's
* lock held. To avoid a AB-BA deadlock (mmap_sem then driver's lock in
* mmap and driver's lock then mmap_sem in prepare_buf) the videobuf2
* core release driver's lock, takes mmap_sem and then takes again
* driver's lock.
*
* To avoid race with other vb2 calls, which might be called after
* releasing driver's lock, this operation is performed at the
* beggining of prepare_buf processing. This way the queue status is
* consistent after getting driver's lock back.
*/
if (q->memory == V4L2_MEMORY_USERPTR) {
mmap_sem = &current->mm->mmap_sem;
call_qop(q, wait_prepare, q);
down_read(mmap_sem);
call_qop(q, wait_finish, q);
}
if (q->fileio) {
dprintk(1, "%s(): file io in progress\n", __func__);
return -EBUSY;
ret = -EBUSY;
goto unlock;
}
if (b->type != q->type) {
dprintk(1, "%s(): invalid buffer type\n", __func__);
return -EINVAL;
ret = -EINVAL;
goto unlock;
}
if (b->index >= q->num_buffers) {
dprintk(1, "%s(): buffer index out of range\n", __func__);
return -EINVAL;
ret = -EINVAL;
goto unlock;
}
vb = q->bufs[b->index];
if (NULL == vb) {
/* Should never happen */
dprintk(1, "%s(): buffer is NULL\n", __func__);
return -EINVAL;
ret = -EINVAL;
goto unlock;
}
if (b->memory != q->memory) {
dprintk(1, "%s(): invalid memory type\n", __func__);
return -EINVAL;
ret = -EINVAL;
goto unlock;
}
if (vb->state != VB2_BUF_STATE_DEQUEUED) {
dprintk(1, "%s(): invalid buffer state %d\n", __func__, vb->state);
return -EINVAL;
ret = -EINVAL;
goto unlock;
}
ret = __verify_planes_array(vb, b);
if (ret < 0)
return ret;
goto unlock;
ret = __buf_prepare(vb, b);
if (ret < 0)
return ret;
goto unlock;
__fill_v4l2_buffer(vb, b);
return 0;
unlock:
if (mmap_sem)
up_read(mmap_sem);
return ret;
}
EXPORT_SYMBOL_GPL(vb2_prepare_buf);
......
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