FAILED: patch "[PATCH] ALSA: usb-audio: Protect Roland control activation" failed to apply to 6.18-stable tree

[Sasha Levin <sashal@kernel.org>]

The patch below does not apply to the 6.18-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.18.y
git checkout FETCH_HEAD
git cherry-pick -x 19b42c1fff7f220a6346c614d79ce1bda6d95b40
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107050744-failed-6.18-19b42c1fff7f@kernel.org' --subject-prefix 'PATCH 6.18.y' 'HEAD^..'

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 19b42c1fff7f220a6346c614d79ce1bda6d95b40 Mon Sep 17 00:00:00 2001
From: Runyu Xiao <runyu.xiao@seu.edu.cn>
Date: Tue, 29 Sep 2026 22:17:26 +0800
Subject: [PATCH] ALSA: usb-audio: Protect Roland control activation

The USB MIDI driver changes the Roland MIDI Input Mode control's access
flags directly from the rawmidi open and close paths.  These changes are
not protected by the ALSA control core and the corresponding notifications
can race with control access.

Use snd_ctl_activate_id() so that the control core updates the access flags
and sends the notification under its lock.  Release the USB MIDI mutex
before calling it because the control write path holds controls_rwsem while
roland_load_put() takes the USB MIDI mutex.

Keep the state transition and alternate-setting change under the USB MIDI
mutex; rawmidi's open mutex serializes the enclosing open and close paths.

Fixes: 96f61d9ade82 ("sound: usb-audio: allow switching altsetting on Roland USB MIDI devices")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>
Link: https://patch.msgid.link/20260929141726.2166899-1-runyu.xiao@seu.edu.cn
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/usb/midi.c | 53 ++++++++++++++++++++++++------------------------
 1 file changed, 27 insertions(+), 26 deletions(-)

diff --git a/sound/usb/midi.c b/sound/usb/midi.c
index 0480a9b89e8f3..e3d1575540613 100644
--- a/sound/usb/midi.c
+++ b/sound/usb/midi.c
@@ -1150,41 +1150,42 @@ static int substream_open(struct snd_rawmidi_substream *substream, int dir,
 			  int open)
 {
 	struct snd_usb_midi *umidi = substream->rmidi->private_data;
-	struct snd_kcontrol *ctl;
+	struct snd_ctl_elem_id ctl_id;
+	bool activate_ctl = false;
+	bool active;
 
 	guard(rwsem_read)(&umidi->disc_rwsem);
 	if (umidi->disconnected)
 		return open ? -ENODEV : 0;
 
-	guard(mutex)(&umidi->mutex);
-	if (open) {
-		if (!umidi->opened[0] && !umidi->opened[1]) {
-			if (umidi->roland_load_ctl) {
-				ctl = umidi->roland_load_ctl;
-				ctl->vd[0].access |=
-					SNDRV_CTL_ELEM_ACCESS_INACTIVE;
-				snd_ctl_notify(umidi->card,
-				       SNDRV_CTL_EVENT_MASK_INFO, &ctl->id);
-				update_roland_altsetting(umidi);
+	scoped_guard(mutex, &umidi->mutex) {
+		if (open) {
+			if (!umidi->opened[0] && !umidi->opened[1]) {
+				if (umidi->roland_load_ctl) {
+					ctl_id = umidi->roland_load_ctl->id;
+					activate_ctl = true;
+					active = false;
+					update_roland_altsetting(umidi);
+				}
 			}
-		}
-		umidi->opened[dir]++;
-		if (umidi->opened[1])
-			snd_usbmidi_input_start(&umidi->list);
-	} else {
-		umidi->opened[dir]--;
-		if (!umidi->opened[1] && !umidi->keep_input_running)
-			snd_usbmidi_input_stop(&umidi->list);
-		if (!umidi->opened[0] && !umidi->opened[1]) {
-			if (umidi->roland_load_ctl) {
-				ctl = umidi->roland_load_ctl;
-				ctl->vd[0].access &=
-					~SNDRV_CTL_ELEM_ACCESS_INACTIVE;
-				snd_ctl_notify(umidi->card,
-				       SNDRV_CTL_EVENT_MASK_INFO, &ctl->id);
+			umidi->opened[dir]++;
+			if (umidi->opened[1])
+				snd_usbmidi_input_start(&umidi->list);
+		} else {
+			umidi->opened[dir]--;
+			if (!umidi->opened[1] && !umidi->keep_input_running)
+				snd_usbmidi_input_stop(&umidi->list);
+			if (!umidi->opened[0] && !umidi->opened[1]) {
+				if (umidi->roland_load_ctl) {
+					ctl_id = umidi->roland_load_ctl->id;
+					activate_ctl = true;
+					active = true;
+				}
 			}
 		}
 	}
+	if (activate_ctl)
+		snd_ctl_activate_id(umidi->card, &ctl_id, active);
 	return 0;
 }
 
-- 
2.53.0