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v4l2allocator: reference memory before the buffer is queued

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In gst_v4l2_allocator_qbuf(), the memory is referenced after the
buffer is queued. Once queued (VIDIOC_QBUF), the buffer might be handled
by the V4L2 driver (e.g. decoded) and dequeued (gst_v4l2_allocator_dqbuf),
through a different thread, before the memory is referenced (gst_memory_ref).
In this case, in gst_v4l2_allocator_dqbuf(), the memory is unreferenced
(gst_memory_unref) before having been referenced: the memory refcount
reaches 0, and the memory is freed.
So, to avoid this crossing case, in gst_v4l2_allocator_qbuf(), the
memory shall be referenced before the buffer is queued.

https://bugzilla.gnome.org/show_bug.cgi?id=777399
This commit is contained in:
Jean-Christophe Trotin 2017-01-17 16:41:58 +01:00 committed by Nicolas Dufresne
parent d1ce68e840
commit 7f763f2710
1 changed files with 9 additions and 4 deletions
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13
sys/v4l2/gstv4l2allocator.c
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@ -1240,9 +1240,18 @@ gst_v4l2_allocator_qbuf (GstV4l2Allocator * allocator,
group->buffer.bytesused = gst_memory_get_sizes (group->mem[0], NULL, NULL);
}
/* Ensure the memory will stay around and is RO */
for (i = 0; i < group->n_mem; i++)
gst_memory_ref (group->mem[i]);
if (v4l2_ioctl (allocator->video_fd, VIDIOC_QBUF, &group->buffer) < 0) {
GST_ERROR_OBJECT (allocator, "failed queueing buffer %i: %s",
group->buffer.index, g_strerror (errno));
/* Release the memory, possibly making it RW again */
for (i = 0; i < group->n_mem; i++)
gst_memory_unref (group->mem[i]);
ret = FALSE;
if (IS_QUEUED (group->buffer)) {
GST_DEBUG_OBJECT (allocator,
@ -1261,10 +1270,6 @@ gst_v4l2_allocator_qbuf (GstV4l2Allocator * allocator,
SET_QUEUED (group->buffer);
}
/* Ensure the memory will stay around and is RO */
for (i = 0; i < group->n_mem; i++)
gst_memory_ref (group->mem[i]);
done:
return ret;
}