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Commit0cbef962ce("PM: sleep: Resume children after resuming the parent") introduced a subtle concurrency issue that may lead to a kernel crash if system suspend is aborted and may also slow down asynchronous device resume otherwise. Namely, the initial list walks in dpm_noirq_resume_devices(), dpm_resume_early(), and dpm_resume() call dpm_clear_async_state() for every device and attempt to asynchronously resume it if it has no children (so it is a "root" device). The asynchronous resume of a root device triggers an attempt to asynchronously resume its children which may take place before calling dpm_clear_async_state() for them due to the lack of synchronization between dpm_async_resume_children() and the code calling dpm_clear_async_state(). If this happens, the dpm_clear_async_state() that comes in late, will clear power.work_in_progress for the given device after it has been set by __dpm_async(), so the suspend callback will be allowed to run once again for the same device during the same transition. This leads to a whole range of interesting breakage. Fortunately, if the suspend transition is not aborted, power.work_in_progress is set by it for all devices, so dpm_async_resume_children() will not schedule asynchronous resume for them until dpm_clear_async_state() clears that flag, but this means missing an opportunity to start the resume of those devices earlier. Address the above issue by adding dpm_list_mtx locking to dpm_async_resume_children(), so it will wait for the entire initial list walk and the invocation of dpm_clear_async_state() for all devices to be completed before scheduling any new asynchronous resume callbacks. Fixes:0cbef962ce("PM: sleep: Resume children after resuming the parent") Link: https://gitlab.freedesktop.org/drm/amd/-/issues/4280 Reported-and-tested-by: Chris Bainbridge <chris.bainbridge@gmail.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Reviewed-by: Mario Limonciello <mario.limonciello@amd.com> Link: https://patch.msgid.link/13779172.uLZWGnKmhe@rjwysocki.net