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    SubjectRe: cpufreq_stats NULL deref on second system suspend
    On 09/12/2013 12:11 PM, Viresh Kumar wrote:
    > On 12 September 2013 11:56, Srivatsa S. Bhat
    > <srivatsa.bhat@linux.vnet.ibm.com> wrote:
    >> I had the same thought when solving this bug.. We have had similar issues with
    >> CPU hotplug notifiers too: why are they invoked in the same order during both
    >> CPU down and up, instead of reversing the order? I even had a patchset to perform
    >> reverse-invocation of notifiers.. http://lwn.net/Articles/508072/
    >> ... but people didn't find that very compelling to have.
    >>
    >
    >> It does to me too, but I think the reason nobody really bothered is because perhaps
    >> not many other subsystems care about the order in which CPUs are torn down or
    >> brought up; they just need the total number to match.. cpufreq is one exception
    >> as we saw with this bug.
    >
    > Probably its time to re-spin that series and make CPUFreq as one of the users
    > of that patchset.. Resume should be just opposite of suspend and so
    > that patchset
    > would make sense even if not many people care about it :)
    >
    > Over that there is one more problem that I see, don't know if it is really a big
    > issue..
    >
    > After a suspend/resume value of policy->cpu may get changed... And so the
    > hierarchy of sysfs cpufreq files too.. Folder that had links to other
    > CPUs folder
    > can now be actual folders instead of links and vice versa..
    >
    > Don't know if this can break something ??
    >

    Interesting observation :-) But we just managed to retain sysfs file permissions
    across suspend/resume with a lot of trouble and regressions. That's probably
    good enough for some time to come ;-) We can retain folder/links when somebody
    really finds a need to do that ;-)

    Of course, if we change the suspend/resume sequence and that fixes this, that
    would be like getting it for free, nobody would say no to it ;-)

    Regards,
    Srivatsa S. Bhat



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