From: Steven Rostedt (Google) rostedt@goodmis.org
commit f0a868788fcbf63cdab51f5adcf73b271ede8164 upstream.
The current code for freeing the emux timer is extremely dangerous:
CPU0 CPU1 ---- ---- snd_emux_timer_callback() snd_emux_free() spin_lock(&emu->voice_lock) del_timer(&emu->tlist); <-- returns immediately spin_unlock(&emu->voice_lock); [..] kfree(emu);
spin_lock(&emu->voice_lock);
[BOOM!]
Instead just use del_timer_sync() which will wait for the timer to finish before continuing. No need to check if the timer is active or not when doing so.
This doesn't fix the race of a possible re-arming of the timer, but at least it won't use the data that has just been freed.
[ Fixed unused variable warning by tiwai ]
Cc: stable@vger.kernel.org Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org Reviewed-by: Guenter Roeck linux@roeck-us.net Link: https://lore.kernel.org/r/20221026231236.6834b551@gandalf.local.home Signed-off-by: Takashi Iwai tiwai@suse.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- sound/synth/emux/emux.c | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-)
--- a/sound/synth/emux/emux.c +++ b/sound/synth/emux/emux.c @@ -125,15 +125,10 @@ EXPORT_SYMBOL(snd_emux_register); */ int snd_emux_free(struct snd_emux *emu) { - unsigned long flags; - if (! emu) return -EINVAL;
- spin_lock_irqsave(&emu->voice_lock, flags); - if (emu->timer_active) - del_timer(&emu->tlist); - spin_unlock_irqrestore(&emu->voice_lock, flags); + del_timer_sync(&emu->tlist);
snd_emux_proc_free(emu); snd_emux_delete_virmidi(emu);