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    SubjectRe: [RFC][PATCH 0/4] Redesign cpu_hotplug locking.
    On Sat, Aug 26, 2006 at 11:46:18PM -0700, Andrew Morton wrote:
    > On Sun, 27 Aug 2006 11:41:55 +0530
    >
    > > The right thing to do would be to
    > > do an audit and clean up the bad lock_cpu_hotplug() calls.
    >
    > No, that won't fix it. For example, take a look at all the *callers* of
    > cpufreq_update_policy(). AFAICT they're all buggy. Fiddling with the
    > existing lock_cpu_hotplug() sites won't fix that. (Possibly this
    > particular problem can be fixed by checking that the relevant CPU is still
    > online after the appropriate locking has been taken - dunno).
    >

    This is a different issue from the ones that relates to lock_cpu_hotplug().
    This one seems like a cpufreq internal locking problem.

    On a quick look at this, it seems to me that cpufreq_cpu_get() should
    do exactly what you said - use a spinlock in each cpufreq_cpu_data[] to
    protect the per-cpu flag and in cpufreq_cpu_get() check if
    !data and data->online == 0. They may have to do -

    static struct cpufreq_data {
    spinlock_t lock;
    int flag;
    struct cpufreq_policy *policy;
    } cpufreq_cpu_data[NR_CPUS];


    Thanks
    Dipankar
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