Messages in this thread | | | Date | Thu, 17 Apr 2014 11:06:40 -0400 | From | Tejun Heo <> | Subject | Re: [RFC PATCH v3] Use kernfs_break_active_protection() for device online store callbacks |
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Hello,
On Thu, Apr 17, 2014 at 11:05:53AM +0800, Li Zhong wrote: > It seems to me cpu_add_remove_lock is always taken after > device_hotplug_lock. > > So if cpu_add_remove_lock has been acquired by device removing process, > then it means the other online/offline process couldn't successfully try > lock device_hotplug_lock, and will release s_active with a restart > syscall error; > > if cpu_add_remove_lock has been acquired by online/offline process, then > it should already hold device_hotlug_lock, and keeps the device removing > process waiting at device_hotplug_lock. So online/offline process could > release the lock, and finally release s_active soon.
I see. That's kinda nasty tho and lockdep of course doesn't know about it and generates spurious warnings.
> But after some further thinking, I seem to understand your point. > s_active has lock order problem with the other series of hotplug related > locks, so it's better to take s_active out of the dependency chain, > rather than the first of the other series of locks? like you suggested > below.
Yeah, I think that'd be the right thing to do and we can revert the previous convolution.
Thanks.
-- tejun
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