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[media] vb2: push the mmap semaphore down to __buf_prepare()

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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>
This commit is contained in:
Hans Verkuil 2013-12-13 13:13:38 -03:00 committed by Mauro Carvalho Chehab
parent b4fcdaf765
commit b18a8ff29d
2 changed files with 38 additions and 46 deletions
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82
drivers/media/v4l2-core/videobuf2-core.c
View file

@ -481,6 +481,7 @@ static void __fill_v4l2_buffer(struct vb2_buffer *vb, struct v4l2_buffer *b)
case VB2_BUF_STATE_PREPARED:
b->flags |= V4L2_BUF_FLAG_PREPARED;
break;
case VB2_BUF_STATE_PREPARING:
case VB2_BUF_STATE_DEQUEUED:
/* nothing */
break;
@ -1228,6 +1229,7 @@ static void __enqueue_in_driver(struct vb2_buffer *vb)
static int __buf_prepare(struct vb2_buffer *vb, const struct v4l2_buffer *b)
{
struct vb2_queue *q = vb->vb2_queue;
struct rw_semaphore *mmap_sem;
int ret;
ret = __verify_length(vb, b);
@ -1237,12 +1239,31 @@ static int __buf_prepare(struct vb2_buffer *vb, const struct v4l2_buffer *b)
return ret;
}
vb->state = VB2_BUF_STATE_PREPARING;
switch (q->memory) {
case V4L2_MEMORY_MMAP:
ret = __qbuf_mmap(vb, b);
break;
case V4L2_MEMORY_USERPTR:
/*
* In case of user pointer buffers vb2 allocators need to get direct
* access to userspace pages. This requires getting the mmap semaphore
* for read access in the current process structure. The same semaphore
* is taken before calling mmap operation, while both qbuf/prepare_buf
* and mmap are called by the driver or v4l2 core with the driver's lock
* held. To avoid an AB-BA deadlock (mmap_sem then driver's lock in mmap
* and driver's lock then mmap_sem in qbuf/prepare_buf) the videobuf2
* core releases the driver's lock, takes mmap_sem and then takes the
* driver's lock again.
*/
mmap_sem = &current->mm->mmap_sem;
call_qop(q, wait_prepare, q);
down_read(mmap_sem);
call_qop(q, wait_finish, q);
ret = __qbuf_userptr(vb, b);
up_read(mmap_sem);
break;
case V4L2_MEMORY_DMABUF:
ret = __qbuf_dmabuf(vb, b);
@ -1256,8 +1277,7 @@ static int __buf_prepare(struct vb2_buffer *vb, const struct v4l2_buffer *b)
ret = call_qop(q, buf_prepare, vb);
if (ret)
dprintk(1, "qbuf: buffer preparation failed: %d\n", ret);
else
vb->state = VB2_BUF_STATE_PREPARED;
vb->state = ret ? VB2_BUF_STATE_DEQUEUED : VB2_BUF_STATE_PREPARED;
return ret;
}
@ -1268,80 +1288,47 @@ static int vb2_queue_or_prepare_buf(struct vb2_queue *q, struct v4l2_buffer *b,
struct v4l2_buffer *,
struct vb2_buffer *))
{
struct rw_semaphore *mmap_sem = NULL;
struct vb2_buffer *vb;
int ret;
/*
* In case of user pointer buffers vb2 allocators need to get direct
* access to userspace pages. This requires getting the mmap semaphore
* for read access in the current process structure. The same semaphore
* is taken before calling mmap operation, while both qbuf/prepare_buf
* and mmap are called by the driver or v4l2 core with the driver's lock
* held. To avoid an AB-BA deadlock (mmap_sem then driver's lock in mmap
* and driver's lock then mmap_sem in qbuf/prepare_buf) the videobuf2
* core releases the driver's lock, takes mmap_sem and then takes the
* driver's lock again.
*
* To avoid racing with other vb2 calls, which might be called after
* releasing the driver's lock, this operation is performed at the
* beginning of qbuf/prepare_buf processing. This way the queue status
* is consistent after getting the 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", opname);
ret = -EBUSY;
goto unlock;
return -EBUSY;
}
if (b->type != q->type) {
dprintk(1, "%s(): invalid buffer type\n", opname);
ret = -EINVAL;
goto unlock;
return -EINVAL;
}
if (b->index >= q->num_buffers) {
dprintk(1, "%s(): buffer index out of range\n", opname);
ret = -EINVAL;
goto unlock;
return -EINVAL;
}
vb = q->bufs[b->index];
if (NULL == vb) {
/* Should never happen */
dprintk(1, "%s(): buffer is NULL\n", opname);
ret = -EINVAL;
goto unlock;
return -EINVAL;
}
if (b->memory != q->memory) {
dprintk(1, "%s(): invalid memory type\n", opname);
ret = -EINVAL;
goto unlock;
return -EINVAL;
}
ret = __verify_planes_array(vb, b);
if (ret)
goto unlock;
return ret;
ret = handler(q, b, vb);
if (ret)
goto unlock;
if (!ret) {
/* Fill buffer information for the userspace */
__fill_v4l2_buffer(vb, b);
/* Fill buffer information for the userspace */
__fill_v4l2_buffer(vb, b);
dprintk(1, "%s() of buffer %d succeeded\n", opname, vb->v4l2_buf.index);
unlock:
if (mmap_sem)
up_read(mmap_sem);
dprintk(1, "%s() of buffer %d succeeded\n", opname, vb->v4l2_buf.index);
}
return ret;
}
@ -1390,6 +1377,9 @@ static int __vb2_qbuf(struct vb2_queue *q, struct v4l2_buffer *b,
return ret;
case VB2_BUF_STATE_PREPARED:
break;
case VB2_BUF_STATE_PREPARING:
dprintk(1, "qbuf: buffer still being prepared\n");
return -EINVAL;
default:
dprintk(1, "qbuf: buffer already in use\n");
return -EINVAL;

2
include/media/videobuf2-core.h
View file

@ -142,6 +142,7 @@ enum vb2_fileio_flags {
/**
* enum vb2_buffer_state - current video buffer state
* @VB2_BUF_STATE_DEQUEUED: buffer under userspace control
* @VB2_BUF_STATE_PREPARING: buffer is being prepared in videobuf
* @VB2_BUF_STATE_PREPARED: buffer prepared in videobuf and by the driver
* @VB2_BUF_STATE_QUEUED: buffer queued in videobuf, but not in driver
* @VB2_BUF_STATE_ACTIVE: buffer queued in driver and possibly used
@ -154,6 +155,7 @@ enum vb2_fileio_flags {
*/
enum vb2_buffer_state {
VB2_BUF_STATE_DEQUEUED,
VB2_BUF_STATE_PREPARING,
VB2_BUF_STATE_PREPARED,
VB2_BUF_STATE_QUEUED,
VB2_BUF_STATE_ACTIVE,