commit 235e089c930efcab982118037c4d51bd0fec20e3
author Takashi Iwai <tiwai@suse.de> Tue Oct 11 09:01:46 2022 +0200
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> Wed Oct 26 13:16:55 2022 +0200
tree 2b96d8890034f591660ab38956d45b3136b80adf
parent 3fd4740cc34cab64575205d1c5b228fad8c8f0f5

ALSA: rawmidi: Drop register_mutex in snd_rawmidi_free()

commit a70aef7982b012e86dfd39fbb235e76a21ae778a upstream.

The register_mutex taken around the dev_unregister callback call in
snd_rawmidi_free() may potentially lead to a mutex deadlock, when OSS
emulation and a hot unplug are involved.

Since the mutex doesn't protect the actual race (as the registration
itself is already protected by another means), let's drop it.

Link: https://lore.kernel.org/r/CAB7eexJP7w1B0mVgDF0dQ+gWor7UdkiwPczmL7pn91xx8xpzOA@mail.gmail.com
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20221011070147.7611-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

sound/core/rawmidi.c

diff --git a/sound/core/rawmidi.c b/sound/core/rawmidi.c
index 0120624..b96b95f 100644
--- a/sound/core/rawmidi.c
+++ b/sound/core/rawmidi.c
@@ -1633,10 +1633,8 @@ static int snd_rawmidi_free(struct snd_rawmidi *rmidi)
 
 	snd_info_free_entry(rmidi->proc_entry);
 	rmidi->proc_entry = NULL;
-	mutex_lock(&register_mutex);
 	if (rmidi->ops && rmidi->ops->dev_unregister)
 		rmidi->ops->dev_unregister(rmidi);
-	mutex_unlock(&register_mutex);
 
 	snd_rawmidi_free_substreams(&rmidi->streams[SNDRV_RAWMIDI_STREAM_INPUT]);
 	snd_rawmidi_free_substreams(&rmidi->streams[SNDRV_RAWMIDI_STREAM_OUTPUT]);