Messages in this thread | | | Date | Wed, 18 Jan 2012 09:30:37 -0800 | From | Tejun Heo <> | Subject | Re: [Update][PATCH] PM / Hibernate: Fix s2disk regression related to unlock_system_sleep() |
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Hello, Srivatsa.
On Wed, Jan 18, 2012 at 10:49:09PM +0530, Srivatsa S. Bhat wrote: > I agree, but I was trying to keep the comment from growing too long ;)
It doesn't have to be long. It just has to give some meaning to the decision. AFAICS, it is correct to call try_to_freeze() on unlock_system_sleep() regardless of 20sec window. There's no guarantee the unlocking task is gonna hit try_to_freeze() elsewhere and not calling it actually makes the interface buggy.
That said, it causes a problem because unlock_system_sleep() is called in a special context during later stage of hibernation where the usual expectation - that a freezable task which sees a freezing condition should freeze - doesn't hold.
The correct solution would be somehow marking that condition so that either try_to_freeze() doesn't get invoked or gets nullified - e.g. making the SKIP thing a counter and ensure the hibernating task has it elevated throughout the whole process. Alternatively, if the code path is limited enough, using a different version of the unlock function, unlock_system_sleep_nofreeze() or whatever, would work too - this is a popular approach for synchronization functions which interacts with scheduler and preemption.
For now, as a quick fix, maybe not calling try_to_freeze() unconditionally is okay, I don't know, but it's a hack.
Thanks.
-- tejun
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