[PATCH] videobuf2/vb2_buffer_done: Changing the position of spinlock to protect only the required code

From: Satendra Singh Thakur
Date: Fri Jul 27 2018 - 04:21:56 EST


1.Currently, in the func vb2_buffer_done, spinlock protects
following code
vb->state = VB2_BUF_STATE_QUEUED;
list_add_tail(&vb->done_entry, &q->done_list);
spin_unlock_irqrestore(&q->done_lock, flags);
vb->state = state;
atomic_dec(&q->owned_by_drv_count);
2.The spinlock is mainly needed to protect list related ops and
vb->state = STATE_ERROR or STATE_DONE as in other funcs
vb2_discard_done
__vb2_get_done_vb
vb2_core_poll.
3. Therefore, spinlock is mainly needed for
list_add, list_del, list_first_entry ops
and state = STATE_DONE and STATE_ERROR to protect
done_list queue.
3. Hence, state = STATE_QUEUED doesn't need spinlock protection.
4. Also atomic_dec dones't require the same as its already atomic.

Signed-off-by: Satendra Singh Thakur <satendra.t@xxxxxxxxxxx>
---
drivers/media/common/videobuf2/videobuf2-core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
index f32ec73..968b403 100644
--- a/drivers/media/common/videobuf2/videobuf2-core.c
+++ b/drivers/media/common/videobuf2/videobuf2-core.c
@@ -923,17 +923,17 @@ void vb2_buffer_done(struct vb2_buffer *vb, enum vb2_buffer_state state)
call_void_memop(vb, finish, vb->planes[plane].mem_priv);
}

- spin_lock_irqsave(&q->done_lock, flags);
if (state == VB2_BUF_STATE_QUEUED ||
state == VB2_BUF_STATE_REQUEUEING) {
vb->state = VB2_BUF_STATE_QUEUED;
} else {
/* Add the buffer to the done buffers list */
+ spin_lock_irqsave(&q->done_lock, flags);
list_add_tail(&vb->done_entry, &q->done_list);
vb->state = state;
+ spin_unlock_irqrestore(&q->done_lock, flags);
}
atomic_dec(&q->owned_by_drv_count);
- spin_unlock_irqrestore(&q->done_lock, flags);

trace_vb2_buf_done(q, vb);

--
2.7.4