[PATCH 6.12.y] ALSA: firewire-motu: Protect register DSP event queue positions

[Sasha Levin <sashal@kernel.org>]

From: Cássio Gabriel <cassiogabrielcontato@gmail.com>

[ Upstream commit 98fb1c1bb11e29eb609b7200a25e136e05aa4498 ]

The register DSP event queue is updated under parser->lock, but
snd_motu_register_dsp_message_parser_count_event() reads pull_pos and
push_pos without the lock.
snd_motu_register_dsp_message_parser_copy_event() also reads both queue
positions before taking the lock.

Protect these accesses with parser->lock as well. This keeps the hwdep
poll/read path consistent with the producer side and with the cached
meter/parameter accessors.

Fixes: 634ec0b2906e ("ALSA: firewire-motu: notify event for parameter change in register DSP model")
Cc: stable@vger.kernel.org
Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>
Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://patch.msgid.link/20260521-alsa-firewire-motu-event-locking-v1-1-708e1c2b5e56@gmail.com
[ converted copy_event() from manual spin_lock_irqsave/spin_unlock_irqrestore to guard(spinlock_irqsave) ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 .../motu/motu-register-dsp-message-parser.c        | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/sound/firewire/motu/motu-register-dsp-message-parser.c b/sound/firewire/motu/motu-register-dsp-message-parser.c
index ef3b0b0f0dab9a..abafae59f365ba 100644
--- a/sound/firewire/motu/motu-register-dsp-message-parser.c
+++ b/sound/firewire/motu/motu-register-dsp-message-parser.c
@@ -393,6 +393,8 @@ unsigned int snd_motu_register_dsp_message_parser_count_event(struct snd_motu *m
 {
 	struct msg_parser *parser = motu->message_parser;
 
+	guard(spinlock_irqsave)(&parser->lock);
+
 	if (parser->pull_pos > parser->push_pos)
 		return EVENT_QUEUE_SIZE - parser->pull_pos + parser->push_pos;
 	else
@@ -402,14 +404,14 @@ unsigned int snd_motu_register_dsp_message_parser_count_event(struct snd_motu *m
 bool snd_motu_register_dsp_message_parser_copy_event(struct snd_motu *motu, u32 *event)
 {
 	struct msg_parser *parser = motu->message_parser;
-	unsigned int pos = parser->pull_pos;
-	unsigned long flags;
+	unsigned int pos;
 
-	if (pos == parser->push_pos)
-		return false;
+	guard(spinlock_irqsave)(&parser->lock);
 
-	spin_lock_irqsave(&parser->lock, flags);
+	if (parser->pull_pos == parser->push_pos)
+		return false;
 
+	pos = parser->pull_pos;
 	*event = parser->event_queue[pos];
 
 	++pos;
@@ -417,7 +419,5 @@ bool snd_motu_register_dsp_message_parser_copy_event(struct snd_motu *motu, u32
 		pos = 0;
 	parser->pull_pos = pos;
 
-	spin_unlock_irqrestore(&parser->lock, flags);
-
 	return true;
 }
-- 
2.53.0