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Imre Deak reported a deadlock of HD-audio driver at unbinding while it's still in probing. Since we probe the codecs asynchronously in a work, the codec driver probe may still be kicked off while the controller itself is being unbound. And, azx_remove() tries to process all pending tasks via cancel_work_sync() for fixing the other races (see commit [0b8c82190c: ALSA: hda - Cancel probe work instead of flush at remove]), now we may meet a bizarre deadlock: Unbind snd_hda_intel via sysfs: device_release_driver() -> device_lock(snd_hda_intel) -> azx_remove() -> cancel_work_sync(azx_probe_work) azx_probe_work(): codec driver probe() -> __driver_attach() -> device_lock(snd_hda_intel) This deadlock is caused by the fact that both device_release_driver() and driver_probe_device() take both the device and its parent locks at the same time. The codec device sets the controller device as its parent, and this lock is taken before the probe() callback is called, while the controller remove() callback gets called also with the same lock. In this patch, as an ugly workaround, we unlock the controller device temporarily during cancel_work_sync() call. The race against another bind call should be still suppressed by the parent's device lock. Reported-by: Imre Deak <imre.deak@intel.com> Fixes:0b8c82190c("ALSA: hda - Cancel probe work instead of flush at remove") Signed-off-by: Takashi Iwai <tiwai@suse.de>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.