Messages in this thread | | | Date | Thu, 11 Jul 2013 10:23:19 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [PATCH] cpufreq: Fix cpufreq regression after suspend/resume |
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On Thu, 11 Jul 2013, Srivatsa S. Bhat wrote:
> Oops! You are right. Hmm, this looks quite difficult to get right :( > There are multiple challenges here: > > 1. The sysfs files must not be removed during cpu_down, and not initialized > > during cpu_up. That would help us preserve the file permissions. > 2. But we should ensure that we really do the cpufreq-core parts of the cpu > initialization during cpu_up. If we fail to free some of the data-structures > during cpu_down, the cpu_up callback will think that a full-init is not > required and not do its job. That will make cpufreq behave erratically after > suspend/resume and take us back to square one. > > 3. A full re-init in the cpu_up callback also involves memory allocations. > So if we don't release the memory in the cpu_down callback, we'll end up > in a memory leak. > > I tried to address all these in this patch, but you found yet another serious > loop-hole. I guess I'm out of ideas now... if anybody has any thoughts on how > to get this right, then I'm all ears. Else, we'll just revert the original > commit like Rafael suggested and leave it upto userspace to save and restore > the permissions across suspend/resume if it wants ;-(
Asking as a naive outsider who is completely unfamiliar with the code, why are any of these things at all troublesome?
Can't cpu_up tell the difference between activating a brand-new CPU and reactivating one that was present before but was temporarily disabled?
Doesn't cpu_up know which data structures get freed when an active CPU is temporarily deactivated?
Doesn't cpu_down know what memory gets allocated in cpu_up? Can't it deallocate just the right parts for the type of transition it is doing?
It sounds like you're really asking how to make sure that cpu_up and cpu_down both know what the other is doing, so that each can do the opposite of the other. That doesn't sound hard.
Alan Stern
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