From 566463afdbc43c7744c5a1b89250fc808df03833 Mon Sep 17 00:00:00 2001
From: Alexandre Courbot <gnurou@gmail.com>
Date: Thu, 27 Aug 2020 14:49:45 +0200
Subject: [PATCH] media: v4l2-mem2mem: always consider OUTPUT queue during poll
Git-commit: 566463afdbc43c7744c5a1b89250fc808df03833
References: git-fixes
Patch-mainline: v5.10-rc1

If poll() is called on a m2m device with the EPOLLOUT event after the
last buffer of the CAPTURE queue is dequeued, any buffer available on
OUTPUT queue will never be signaled because v4l2_m2m_poll_for_data()
starts by checking whether dst_q->last_buffer_dequeued is set and
returns EPOLLIN in this case, without looking at the state of the OUTPUT
queue.

Fix this by not early returning so we keep checking the state of the
OUTPUT queue afterwards.

Signed-off-by: Alexandre Courbot <gnurou@gmail.com>
Reviewed-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 drivers/media/v4l2-core/v4l2-mem2mem.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c
index 6a80240e9228..121243e5bece 100644
--- a/drivers/media/v4l2-core/v4l2-mem2mem.c
+++ b/drivers/media/v4l2-core/v4l2-mem2mem.c
@@ -909,10 +909,8 @@ static __poll_t v4l2_m2m_poll_for_data(struct file *file,
 		 * If the last buffer was dequeued from the capture queue,
 		 * return immediately. DQBUF will return -EPIPE.
 		 */
-		if (dst_q->last_buffer_dequeued) {
-			spin_unlock_irqrestore(&dst_q->done_lock, flags);
-			return EPOLLIN | EPOLLRDNORM;
-		}
+		if (dst_q->last_buffer_dequeued)
+			rc |= EPOLLIN | EPOLLRDNORM;
 	}
 	spin_unlock_irqrestore(&dst_q->done_lock, flags);
 
-- 
2.35.3