Messages in this thread | | | Date | Thu, 1 Dec 2022 14:32:26 +0000 | Subject | Re: [PATCH] soundwire: bus_type: Avoid lockdep assert in sdw_drv_probe() | From | Richard Fitzgerald <> |
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On 29/11/2022 15:44, Pierre-Louis Bossart wrote: > > >>>> Don't hold sdw_dev_lock while calling the peripheral driver >>>> probe() and remove() callbacks. >>>> >>>> Holding sdw_dev_lock around the probe() and remove() calls >>>> causes a theoretical mutex inversion which lockdep will >>>> assert on. The peripheral driver probe will probably register >>>> a soundcard, which will take ALSA and ASoC locks. During >>> >>> It's extremely unlikely that a peripheral driver would register a sound >>> card, this is what machine drivers do. >>> >>> Which leads me to the question: is this a real problem? >>> >> >> Yes, try turning on lockdep checking and you will get an assert. >> During probe the existing code takes sdw_dev_lock and then calls the >> codec driver probe, so you will get a mutex sequence like: >> >> sdw_dev_lock -> controls_rw_sem -> pcm_mutex >> >> but in normal operation the ALSA/ASoC code will take its mutexes first >> and call runtime_resume which then takes the sdw_dev_lock, so you get >> >> pcm_mutex -> sdw_dev_lock >> >> and lockdep will assert on that opposite ordering. >> The full assert is at the end of this email. > > Humm, you lost me with the reference to runtime_resume. I don't fully > understand how it's possible to invoke pm_runtime during probe. > pm_runtime should only enabled during the codec update_status() which > can only be done once the probe completes. > > I am fine with the changes that you are suggesting, the introduction of > the sdw_dev_lock was probably too conservative and it'd be fine to only > protect what is required. > > However we do have lockdep enabled >
I wonder whether this is because the Cirrus devices use full DP prepare, so there will be a DP prepare interrupt during the attempt to prepare the dailink. The lockdep assert was when sdw_update_slave_status() tried to take sdw_dev_lock.
If the Realtek codecs only use Soundwire interrupts for jack detect you probably won't see a sdw_dev_lock inside a pcm_mutex.
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