On Thu, 06 Jul 2023 17:16:38 +0200,
Amadeusz Sławiński wrote:
>
> On 7/5/2023 4:47 PM, Amadeusz Sławiński wrote:
> > 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.
>
> I've run tests and see nothing worrying, so
> Tested-by: Amadeusz Sławiński <amadeuszx.slawinski@xxxxxxxxxxxxxxx>
Good to hear, I'll submit the proper patch.
thanks,
Takashi
