[PATCH 2/2] ALSA: hdspm: Take hdspm->lock when masking MIDI interrupts in IRQ handler

[Yifei Gao <gyf161023@gmail.com>]

snd_hdspm_interrupt() clears a MIDI interrupt enable bit in
hdspm->control_register without hdspm->lock. Every other update holds
that lock. This includes snd_hdspm_midi_input_read(), which sets the bit
again, since commit c0da00145f9a ("ALSA: hdspm - Fix locking in
snd_hdspm_midi_input_read"). Updates racing with the handler on another
CPU can be lost. This can stall MIDI input or revert a control setting.

Take hdspm->lock in the handler. All other users of the lock already
run with interrupts disabled.

Found by static analysis. Compile-tested only; no hardware available.

Fixes: 763f356cd8de ("[ALSA] Add HDSP MADI driver")
Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Yifei Gao <gyf161023@gmail.com>
---
 sound/pci/rme9652/hdspm.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/sound/pci/rme9652/hdspm.c b/sound/pci/rme9652/hdspm.c
index cc4cf43e5a5b..135761278556 100644
--- a/sound/pci/rme9652/hdspm.c
+++ b/sound/pci/rme9652/hdspm.c
@@ -5383,9 +5383,11 @@ static irqreturn_t snd_hdspm_interrupt(int irq, void *dev_id)
 				/* we disable interrupts for this input until
 				 * processing is done
 				 */
-				hdspm->control_register &= ~hdspm->midi[i].ie;
-				hdspm_write(hdspm, HDSPM_controlRegister,
-						hdspm->control_register);
+				scoped_guard(spinlock, &hdspm->lock) {
+					hdspm->control_register &= ~hdspm->midi[i].ie;
+					hdspm_write(hdspm, HDSPM_controlRegister,
+						    hdspm->control_register);
+				}
 				hdspm->midi[i].pending = 1;
 				schedule = 1;
 			}
-- 
2.34.1