linux-kernel - [PATCH] media: usbtv: Fix deadlock on suspend

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Date:   Sat,  6 Feb 2021 00:51:39 +0200
From:   Maxim Mikityanskiy <maxtram95@...il.com>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Federico Simoncelli <fsimonce@...hat.com>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>
Cc:     Lubomir Rintel <lkundrak@...sk>, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Maxim Mikityanskiy <maxtram95@...il.com>
Subject: [PATCH] media: usbtv: Fix deadlock on suspend

usbtv doesn't support power management, so on system suspend the
.disconnect callback of the driver is called. The teardown sequence
includes a call to snd_card_free. Its implementation waits until the
refcount of the sound card device drops to zero, however, if its file is
open, snd_card_file_add takes a reference, which can't be dropped during
the suspend, because the userspace processes are already frozen at this
point. snd_card_free waits for completion forever, leading to a hang on
suspend.

This commit fixes this deadlock condition by replacing snd_card_free
with snd_card_free_when_closed, that doesn't wait until all references
are released, allowing suspend to progress.

Fixes: 63ddf68de52e ("[media] usbtv: add audio support")
Signed-off-by: Maxim Mikityanskiy <maxtram95@...il.com>
---
 drivers/media/usb/usbtv/usbtv-audio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/media/usb/usbtv/usbtv-audio.c b/drivers/media/usb/usbtv/usbtv-audio.c
index b57e94fb1977..333bd305a4f9 100644
--- a/drivers/media/usb/usbtv/usbtv-audio.c
+++ b/drivers/media/usb/usbtv/usbtv-audio.c
@@ -371,7 +371,7 @@ void usbtv_audio_free(struct usbtv *usbtv)
 	cancel_work_sync(&usbtv->snd_trigger);

 	if (usbtv->snd && usbtv->udev) {
-		snd_card_free(usbtv->snd);
+		snd_card_free_when_closed(usbtv->snd);
 		usbtv->snd = NULL;
 	}
 }
-- 
2.30.0