linux-kernel - [PATCH 6.0 169/862] media: cedrus: Fix watchdog race condition

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Date:   Wed, 19 Oct 2022 10:24:16 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Mauro Carvalho Chehab <mchehab@...nel.org>
Subject: [PATCH 6.0 169/862] media: cedrus: Fix watchdog race condition

From: Nicolas Dufresne <nicolas.dufresne@...labora.com>

commit fe8b81fde69acfcbb5af9e85328e5b9549999fdb upstream.

The watchdog needs to be scheduled before we trigger the decode
operation, otherwise there is a risk that the decoder IRQ will be
called before we have schedule the watchdog. As a side effect, the
watchdog would never be cancelled and its function would be called
at an inappropriate time.

This was observed while running Fluster with GStreamer as a backend.
Some programming error would cause the decoder IRQ to be call very
quickly after the trigger. Later calls into the driver would deadlock
due to the unbalanced state.

Cc: stable@...r.kernel.org
Fixes: 7c38a551bda1 ("media: cedrus: Add watchdog for job completion")
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@...labora.com>
Reviewed-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
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/staging/media/sunxi/cedrus/cedrus_dec.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
+++ b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
@@ -106,11 +106,11 @@ void cedrus_device_run(void *priv)
 
 	/* Trigger decoding if setup went well, bail out otherwise. */
 	if (!error) {
-		dev->dec_ops[ctx->current_codec]->trigger(ctx);
-
 		/* Start the watchdog timer. */
 		schedule_delayed_work(&dev->watchdog_work,
 				      msecs_to_jiffies(2000));
+
+		dev->dec_ops[ctx->current_codec]->trigger(ctx);
 	} else {
 		v4l2_m2m_buf_done_and_job_finish(ctx->dev->m2m_dev,
 						 ctx->fh.m2m_ctx,