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 -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
