[media] vb2: push the mmap semaphore down to __buf_prepare()
Rather than taking the mmap semaphore at a relatively high-level function, push it down to the place where it is really needed. It was placed in vb2_queue_or_prepare_buf() to prevent racing with other vb2 calls. The only way I can see that a race can happen is when two threads queue the same buffer. The solution for that it to introduce a PREPARING state. Moving it down offers opportunities to simplify the code. Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com> Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
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@ -481,6 +481,7 @@ static void __fill_v4l2_buffer(struct vb2_buffer *vb, struct v4l2_buffer *b)
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case VB2_BUF_STATE_PREPARED:
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b->flags |= V4L2_BUF_FLAG_PREPARED;
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break;
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case VB2_BUF_STATE_PREPARING:
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case VB2_BUF_STATE_DEQUEUED:
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/* nothing */
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break;
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@ -1228,6 +1229,7 @@ static void __enqueue_in_driver(struct vb2_buffer *vb)
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static int __buf_prepare(struct vb2_buffer *vb, const struct v4l2_buffer *b)
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{
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struct vb2_queue *q = vb->vb2_queue;
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struct rw_semaphore *mmap_sem;
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int ret;
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ret = __verify_length(vb, b);
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@ -1237,12 +1239,31 @@ static int __buf_prepare(struct vb2_buffer *vb, const struct v4l2_buffer *b)
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return ret;
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}
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vb->state = VB2_BUF_STATE_PREPARING;
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switch (q->memory) {
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case V4L2_MEMORY_MMAP:
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ret = __qbuf_mmap(vb, b);
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break;
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case V4L2_MEMORY_USERPTR:
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/*
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* In case of user pointer buffers vb2 allocators need to get direct
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* access to userspace pages. This requires getting the mmap semaphore
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* for read access in the current process structure. The same semaphore
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* is taken before calling mmap operation, while both qbuf/prepare_buf
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* and mmap are called by the driver or v4l2 core with the driver's lock
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* held. To avoid an AB-BA deadlock (mmap_sem then driver's lock in mmap
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* and driver's lock then mmap_sem in qbuf/prepare_buf) the videobuf2
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* core releases the driver's lock, takes mmap_sem and then takes the
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* driver's lock again.
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*/
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mmap_sem = ¤t->mm->mmap_sem;
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call_qop(q, wait_prepare, q);
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down_read(mmap_sem);
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call_qop(q, wait_finish, q);
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ret = __qbuf_userptr(vb, b);
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up_read(mmap_sem);
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break;
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case V4L2_MEMORY_DMABUF:
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ret = __qbuf_dmabuf(vb, b);
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@ -1256,8 +1277,7 @@ static int __buf_prepare(struct vb2_buffer *vb, const struct v4l2_buffer *b)
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ret = call_qop(q, buf_prepare, vb);
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if (ret)
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dprintk(1, "qbuf: buffer preparation failed: %d\n", ret);
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else
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vb->state = VB2_BUF_STATE_PREPARED;
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vb->state = ret ? VB2_BUF_STATE_DEQUEUED : VB2_BUF_STATE_PREPARED;
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return ret;
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}
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@ -1268,80 +1288,47 @@ static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct v4l2_buffer *b,
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struct v4l2_buffer *,
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struct vb2_buffer *))
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{
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struct rw_semaphore *mmap_sem = NULL;
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struct vb2_buffer *vb;
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int ret;
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/*
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* In case of user pointer buffers vb2 allocators need to get direct
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* access to userspace pages. This requires getting the mmap semaphore
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* for read access in the current process structure. The same semaphore
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* is taken before calling mmap operation, while both qbuf/prepare_buf
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* and mmap are called by the driver or v4l2 core with the driver's lock
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* held. To avoid an AB-BA deadlock (mmap_sem then driver's lock in mmap
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* and driver's lock then mmap_sem in qbuf/prepare_buf) the videobuf2
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* core releases the driver's lock, takes mmap_sem and then takes the
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* driver's lock again.
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*
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* To avoid racing with other vb2 calls, which might be called after
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* releasing the driver's lock, this operation is performed at the
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* beginning of qbuf/prepare_buf processing. This way the queue status
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* is consistent after getting the driver's lock back.
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*/
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if (q->memory == V4L2_MEMORY_USERPTR) {
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mmap_sem = ¤t->mm->mmap_sem;
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call_qop(q, wait_prepare, q);
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down_read(mmap_sem);
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call_qop(q, wait_finish, q);
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}
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if (q->fileio) {
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dprintk(1, "%s(): file io in progress\n", opname);
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ret = -EBUSY;
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goto unlock;
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return -EBUSY;
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}
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if (b->type != q->type) {
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dprintk(1, "%s(): invalid buffer type\n", opname);
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ret = -EINVAL;
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goto unlock;
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return -EINVAL;
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}
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if (b->index >= q->num_buffers) {
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dprintk(1, "%s(): buffer index out of range\n", opname);
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ret = -EINVAL;
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goto unlock;
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return -EINVAL;
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}
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vb = q->bufs[b->index];
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if (NULL == vb) {
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/* Should never happen */
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dprintk(1, "%s(): buffer is NULL\n", opname);
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ret = -EINVAL;
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goto unlock;
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return -EINVAL;
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}
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if (b->memory != q->memory) {
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dprintk(1, "%s(): invalid memory type\n", opname);
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ret = -EINVAL;
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goto unlock;
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return -EINVAL;
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}
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ret = __verify_planes_array(vb, b);
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if (ret)
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goto unlock;
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return ret;
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ret = handler(q, b, vb);
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if (ret)
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goto unlock;
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if (!ret) {
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/* Fill buffer information for the userspace */
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__fill_v4l2_buffer(vb, b);
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/* Fill buffer information for the userspace */
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__fill_v4l2_buffer(vb, b);
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dprintk(1, "%s() of buffer %d succeeded\n", opname, vb->v4l2_buf.index);
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unlock:
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if (mmap_sem)
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up_read(mmap_sem);
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dprintk(1, "%s() of buffer %d succeeded\n", opname, vb->v4l2_buf.index);
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}
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return ret;
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}
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@ -1390,6 +1377,9 @@ static int __vb2_qbuf(struct vb2_queue *q, struct v4l2_buffer *b,
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return ret;
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case VB2_BUF_STATE_PREPARED:
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break;
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case VB2_BUF_STATE_PREPARING:
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dprintk(1, "qbuf: buffer still being prepared\n");
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return -EINVAL;
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default:
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dprintk(1, "qbuf: buffer already in use\n");
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return -EINVAL;
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@ -142,6 +142,7 @@ enum vb2_fileio_flags {
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/**
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* enum vb2_buffer_state - current video buffer state
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* @VB2_BUF_STATE_DEQUEUED: buffer under userspace control
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* @VB2_BUF_STATE_PREPARING: buffer is being prepared in videobuf
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* @VB2_BUF_STATE_PREPARED: buffer prepared in videobuf and by the driver
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* @VB2_BUF_STATE_QUEUED: buffer queued in videobuf, but not in driver
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* @VB2_BUF_STATE_ACTIVE: buffer queued in driver and possibly used
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@ -154,6 +155,7 @@ enum vb2_fileio_flags {
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*/
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enum vb2_buffer_state {
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VB2_BUF_STATE_DEQUEUED,
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VB2_BUF_STATE_PREPARING,
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VB2_BUF_STATE_PREPARED,
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VB2_BUF_STATE_QUEUED,
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VB2_BUF_STATE_ACTIVE,
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