The recent change in lockdep for read lock caused the deadlock warnings in ALSA control code which uses the read_lock() for notification and else while write_lock_irqsave() is used for adding and removing the list entry. Although a deadlock would practically never hit in a real usage (the addition and the deletion can't happen with the notification), it's better to fix the read_lock() usage in a semantically correct way.
This patch replaces the read_lock() calls with read_lock_irqsave() version for avoiding a reported deadlock. The notification code path takes the irq disablement in anyway, and other code paths are very short execution, hence there shouldn't be any big performance hit by this change.
Fixes: e918188611f0 ("locking: More accurate annotations for read_lock()") Reported-by: syzbot+561a74f84100162990b2@syzkaller.appspotmail.com Signed-off-by: Takashi Iwai tiwai@suse.de --- sound/core/control.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-)
diff --git a/sound/core/control.c b/sound/core/control.c index e014598142df..421ddc76f264 100644 --- a/sound/core/control.c +++ b/sound/core/control.c @@ -150,14 +150,14 @@ void snd_ctl_notify(struct snd_card *card, unsigned int mask, return; if (card->shutdown) return; - read_lock(&card->ctl_files_rwlock); + read_lock_irqsave(&card->ctl_files_rwlock, flags); #if IS_ENABLED(CONFIG_SND_MIXER_OSS) card->mixer_oss_change_count++; #endif list_for_each_entry(ctl, &card->ctl_files, list) { if (!ctl->subscribed) continue; - spin_lock_irqsave(&ctl->read_lock, flags); + spin_lock(&ctl->read_lock); list_for_each_entry(ev, &ctl->events, list) { if (ev->id.numid == id->numid) { ev->mask |= mask; @@ -174,10 +174,10 @@ void snd_ctl_notify(struct snd_card *card, unsigned int mask, } _found: wake_up(&ctl->change_sleep); - spin_unlock_irqrestore(&ctl->read_lock, flags); + spin_unlock(&ctl->read_lock); kill_fasync(&ctl->fasync, SIGIO, POLL_IN); } - read_unlock(&card->ctl_files_rwlock); + read_unlock_irqrestore(&card->ctl_files_rwlock, flags); } EXPORT_SYMBOL(snd_ctl_notify);
@@ -1951,8 +1951,9 @@ int snd_ctl_get_preferred_subdevice(struct snd_card *card, int type) { struct snd_ctl_file *kctl; int subdevice = -1; + unsigned long flags;
- read_lock(&card->ctl_files_rwlock); + read_lock_irqsave(&card->ctl_files_rwlock, flags); list_for_each_entry(kctl, &card->ctl_files, list) { if (kctl->pid == task_pid(current)) { subdevice = kctl->preferred_subdevice[type]; @@ -1960,7 +1961,7 @@ int snd_ctl_get_preferred_subdevice(struct snd_card *card, int type) break; } } - read_unlock(&card->ctl_files_rwlock); + read_unlock_irqrestore(&card->ctl_files_rwlock, flags); return subdevice; } EXPORT_SYMBOL_GPL(snd_ctl_get_preferred_subdevice); @@ -2009,13 +2010,14 @@ static int snd_ctl_dev_disconnect(struct snd_device *device) { struct snd_card *card = device->device_data; struct snd_ctl_file *ctl; + unsigned long flags;
- read_lock(&card->ctl_files_rwlock); + read_lock_irqsave(&card->ctl_files_rwlock, flags); list_for_each_entry(ctl, &card->ctl_files, list) { wake_up(&ctl->change_sleep); kill_fasync(&ctl->fasync, SIGIO, POLL_ERR); } - read_unlock(&card->ctl_files_rwlock); + read_unlock_irqrestore(&card->ctl_files_rwlock, flags);
return snd_unregister_device(&card->ctl_dev); }