linux-kernel - [PATCH 5.4 055/168] media: usbtv: Fix deadlock on suspend

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Message-Id: <20210315135552.166965723@linuxfoundation.org>
Date:   Mon, 15 Mar 2021 14:54:47 +0100
From:   gregkh@...uxfoundation.org
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Maxim Mikityanskiy <maxtram95@...il.com>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Subject: [PATCH 5.4 055/168] media: usbtv: Fix deadlock on suspend

From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

From: Maxim Mikityanskiy <maxtram95@...il.com>

commit 8a7e27fd5cd696ba564a3f62cedef7269cfd0723 upstream.

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>
Signed-off-by: Hans Verkuil <hverkuil-cisco@...all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/media/usb/usbtv/usbtv-audio.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/media/usb/usbtv/usbtv-audio.c
+++ b/drivers/media/usb/usbtv/usbtv-audio.c
@@ -399,7 +399,7 @@ void usbtv_audio_free(struct usbtv *usbt
 	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;
 	}
 }