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From:   Nicolas Dufresne <nicolas.dufresne@collabora.com>
To:     linux-media@vger.kernel.org, Maxime Ripard <mripard@kernel.org>,
        Paul Kocialkowski <paul.kocialkowski@bootlin.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Chen-Yu Tsai <wens@csie.org>,
        Jernej Skrabec <jernej.skrabec@gmail.com>,
        Samuel Holland <samuel@sholland.org>,
        Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc:     kernel@collabora.com,
        Nicolas Dufresne <nicolas.dufresne@collabora.com>,
        stable@vger.kernel.org, linux-staging@lists.linux.dev,
        linux-arm-kernel@lists.infradead.org, linux-sunxi@lists.linux.dev,
        linux-kernel@vger.kernel.org
Subject: [PATCH v1 1/3] media: cedrus: Fix watchdog race condition
Date:   Thu, 18 Aug 2022 16:33:06 -0400
Message-Id: <20220818203308.439043-2-nicolas.dufresne@collabora.com>
In-Reply-To: <20220818203308.439043-1-nicolas.dufresne@collabora.com>
References: <20220818203308.439043-1-nicolas.dufresne@collabora.com>
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The watchdog needs to be schedule 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@vger.kernel.org
Fixes: 7c38a551bda1 ("media: cedrus: Add watchdog for job completion")
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
---
 drivers/staging/media/sunxi/cedrus/cedrus_dec.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_dec.c b/drivers/staging/media/sunxi/cedrus/cedrus_dec.c
index 3b6aa78a2985f..e7f7602a5ab40 100644
--- 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,
-- 
2.37.2