On 7/4/2023 10:07 AM, Takashi Iwai wrote:
On Mon, 03 Jul 2023 16:18:27 +0200, Dan Carpenter wrote:
Hello Amadeusz Sławiński,
The patch 1b6a6fc5280e: "ALSA: jack: Access input_dev under mutex" from Apr 12, 2022, leads to the following Smatch static checker warning:
sound/core/jack.c:673 snd_jack_report() warn: sleeping in atomic context
sound/core/jack.c 663 jack->hw_status_cache = status; 664 665 list_for_each_entry(jack_kctl, &jack->kctl_list, list) 666 if (jack_kctl->sw_inject_enable) 667 mask_bits |= jack_kctl->mask_bits; 668 else 669 snd_kctl_jack_report(jack->card, jack_kctl->kctl, 670 status & jack_kctl->mask_bits); 671 672 #ifdef CONFIG_SND_JACK_INPUT_DEV --> 673 mutex_lock(&jack->input_dev_lock); ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
That patch adds this mutex but we can't take mutex because we're already holding a spinlock. The problematic call trees are:
virtsnd_event_notify_cb() <- disables preempt virtsnd_disable_event_vq() <- disables preempt -> virtsnd_event_dispatch() -> virtsnd_jack_event() -> snd_jack_report()
The virtsnd_event_notify_cb() and virtsnd_disable_event_vq() functions take the spin_lock_irqsave(&queue->lock, flags);
Indeed it was no good choice to use the mutex there inside the report function. It's supposed to be callable from an irq-disabled context, too.
How about simply using the device refcount like below?
Although we may drop the mutex from snd_jack, it can can be left, as it's still useful for protecting a potential race between creation and deletion.
thanks,
Takashi
-- 8< -- --- a/sound/core/jack.c +++ b/sound/core/jack.c @@ -654,6 +654,7 @@ void snd_jack_report(struct snd_jack *jack, int status) struct snd_jack_kctl *jack_kctl; unsigned int mask_bits = 0; #ifdef CONFIG_SND_JACK_INPUT_DEV
- struct input_dev *idev; int i; #endif
@@ -670,17 +671,15 @@ void snd_jack_report(struct snd_jack *jack, int status) status & jack_kctl->mask_bits);
#ifdef CONFIG_SND_JACK_INPUT_DEV
- mutex_lock(&jack->input_dev_lock);
- if (!jack->input_dev) {
mutex_unlock(&jack->input_dev_lock);
- idev = input_get_device(jack->input_dev);
- if (!idev) return;
}
for (i = 0; i < ARRAY_SIZE(jack->key); i++) { int testbit = ((SND_JACK_BTN_0 >> i) & ~mask_bits);
if (jack->type & testbit)
input_report_key(jack->input_dev, jack->key[i],
input_report_key(idev, jack->key[i], status & testbit);@@ -688,13 +687,13 @@ void snd_jack_report(struct snd_jack *jack, int status) int testbit = ((1 << i) & ~mask_bits);
if (jack->type & testbit)
input_report_switch(jack->input_dev,
input_report_switch(idev, jack_switch_types[i], status & testbit);
- input_sync(jack->input_dev);
- mutex_unlock(&jack->input_dev_lock);
- input_sync(idev);
- input_put_device(idev); #endif /* CONFIG_SND_JACK_INPUT_DEV */ } EXPORT_SYMBOL(snd_jack_report);
Looking at code it looks like it should also work. Will schedule test run tomorrow to see if it causes any problems.