ALSA: Fix yet another race in disconnection

This patch fixes a race between snd_card_file_remove() and
snd_card_disconnect().  When the card is added to shutdown_files list
in snd_card_disconnect(), but it's freed in snd_card_file_remove() at
the same time, the shutdown_files list gets corrupted.  The list member
must be freed in snd_card_file_remove() as well.
Reported-and-tested-by: Russ Dill <russ.dill@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/init.c

@@ -848,6 +848,7 @@ int snd_card_file_add(struct snd_card *card, struct file *file)
 		return -ENOMEM;
 	mfile->file = file;
 	mfile->disconnected_f_op = NULL;
+	INIT_LIST_HEAD(&mfile->shutdown_list);
 	spin_lock(&card->files_lock);
 	if (card->shutdown) {
 		spin_unlock(&card->files_lock);
@@ -883,6 +884,9 @@ int snd_card_file_remove(struct snd_card *card, struct file *file)
 	list_for_each_entry(mfile, &card->files_list, list) {
 		if (mfile->file == file) {
 			list_del(&mfile->list);
+			spin_lock(&shutdown_lock);
+			list_del(&mfile->shutdown_list);
+			spin_unlock(&shutdown_lock);
 			if (mfile->disconnected_f_op)
 				fops_put(mfile->disconnected_f_op);
 			found = mfile;