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[media] vb2: fix race condition between REQBUFS and QBUF/PREPARE_BUF 

When preparing a buffer the queue lock is released for a short while
if the memory mode is USERPTR (see __buf_prepare for the details), which
would allow a race with a REQBUFS which can free the buffers. Removing the
buffers from underneath __buf_prepare is obviously a bad idea, so we
check if any of the buffers is in the state PREPARING, and if so we
just return -EAGAIN.

If this happens, then the application does something really strange. The
REQBUFS call can be retried safely, since this situation is transient.

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 13:13:40 -03:00 committed by Mauro Carvalho Chehab
parent 4138111a27
commit 63faabfd89
1 changed files with 23 additions and 2 deletions
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25
drivers/media/v4l2-core/videobuf2-core.c
View File

@ -298,10 +298,28 @@ static void __vb2_free_mem(struct vb2_queue *q, unsigned int buffers)
* related information, if no buffers are left return the queue to an * related information, if no buffers are left return the queue to an
* uninitialized state. Might be called even if the queue has already been freed. * uninitialized state. Might be called even if the queue has already been freed.
*/ */
static void __vb2_queue_free(struct vb2_queue *q, unsigned int buffers) static int __vb2_queue_free(struct vb2_queue *q, unsigned int buffers)
{ {
unsigned int buffer; unsigned int buffer;
/*
* Sanity check: when preparing a buffer the queue lock is released for
* a short while (see __buf_prepare for the details), which would allow
* a race with a reqbufs which can call this function. Removing the
* buffers from underneath __buf_prepare is obviously a bad idea, so we
* check if any of the buffers is in the state PREPARING, and if so we
* just return -EAGAIN.
*/
for (buffer = q->num_buffers - buffers; buffer < q->num_buffers;
++buffer) {
if (q->bufs[buffer] == NULL)
continue;
if (q->bufs[buffer]->state == VB2_BUF_STATE_PREPARING) {
dprintk(1, "reqbufs: preparing buffers, cannot free\n");
return -EAGAIN;
}
}
/* Call driver-provided cleanup function for each buffer, if provided */ /* Call driver-provided cleanup function for each buffer, if provided */
if (q->ops->buf_cleanup) { if (q->ops->buf_cleanup) {
for (buffer = q->num_buffers - buffers; buffer < q->num_buffers; for (buffer = q->num_buffers - buffers; buffer < q->num_buffers;
@ -326,6 +344,7 @@ static void __vb2_queue_free(struct vb2_queue *q, unsigned int buffers)
if (!q->num_buffers) if (!q->num_buffers)
q->memory = 0; q->memory = 0;
INIT_LIST_HEAD(&q->queued_list); INIT_LIST_HEAD(&q->queued_list);
return 0;
} }
/** /**
@ -658,7 +677,9 @@ static int __reqbufs(struct vb2_queue *q, struct v4l2_requestbuffers *req)
return -EBUSY; return -EBUSY;
} }
__vb2_queue_free(q, q->num_buffers); ret = __vb2_queue_free(q, q->num_buffers);
if (ret)
return ret;
/* /*
* In case of REQBUFS(0) return immediately without calling * In case of REQBUFS(0) return immediately without calling