linux-kernel - [PATCH 5.4 154/203] media: coda: fix deadlock between decoder picture run and start command

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Message-Id: <20200116231758.296412614@linuxfoundation.org>
Date:   Fri, 17 Jan 2020 00:17:51 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Philipp Zabel <p.zabel@...gutronix.de>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Subject: [PATCH 5.4 154/203] media: coda: fix deadlock between decoder picture run and start command

From: Philipp Zabel <p.zabel@...gutronix.de>

commit a3fd80198de6ab98a205cf7fb148d88e9e1c44bb upstream.

The BIT decoder picture run temporarily locks the bitstream mutex while
the coda device mutex is locked, to refill the bitstream ring buffer.
Consequently, the decoder start command, which locks both mutexes when
flushing the bitstream ring buffer, must lock the coda device mutex
first as well, to avoid an ABBA deadlock.

Fixes: e7fd95849b3c ("media: coda: flush bitstream ring buffer on decoder restart")
Signed-off-by: Philipp Zabel <p.zabel@...gutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@...all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/media/platform/coda/coda-common.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/media/platform/coda/coda-common.c
+++ b/drivers/media/platform/coda/coda-common.c
@@ -1084,16 +1084,16 @@ static int coda_decoder_cmd(struct file
 
 	switch (dc->cmd) {
 	case V4L2_DEC_CMD_START:
-		mutex_lock(&ctx->bitstream_mutex);
 		mutex_lock(&dev->coda_mutex);
+		mutex_lock(&ctx->bitstream_mutex);
 		coda_bitstream_flush(ctx);
-		mutex_unlock(&dev->coda_mutex);
 		dst_vq = v4l2_m2m_get_vq(ctx->fh.m2m_ctx,
 					 V4L2_BUF_TYPE_VIDEO_CAPTURE);
 		vb2_clear_last_buffer_dequeued(dst_vq);
 		ctx->bit_stream_param &= ~CODA_BIT_STREAM_END_FLAG;
 		coda_fill_bitstream(ctx, NULL);
 		mutex_unlock(&ctx->bitstream_mutex);
+		mutex_unlock(&dev->coda_mutex);
 		break;
 	case V4L2_DEC_CMD_STOP:
 		stream_end = false;