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    SubjectRe: 2.6.16 - sys_sched_getaffinity & hotplug
    Ingo Molnar wrote:
    >
    > > Jack wrote:
    > > > Should the following change be made to sched_getaffinity().
    > > >
    > > > Index: linux/kernel/sched.c
    > > > ===================================================================
    > > > --- linux.orig/kernel/sched.c 2006-01-25 08:50:21.401747695 -0600
    > > > +++ linux/kernel/sched.c 2006-01-27 16:57:24.504871895 -0600
    > > > @@ -4031,7 +4031,7 @@ long sched_getaffinity(pid_t pid, cpumas
    > > > goto out_unlock;
    > > >
    > > > retval = 0;
    > > > - cpus_and(*mask, p->cpus_allowed, cpu_possible_map);
    > > > + cpus_and(*mask, p->cpus_allowed, cpu_online_map);
    > >
    > In any case, Jack's change looks reasonable and obviously correct.

    Are you sure? Assuming this change is in effect, consider the
    following:

    Task starts with default affinity.

    Task does sched_getaffinity, stashes the result in saved_mask.

    Task pins itself to one cpu and does some work.

    Meanwhile, more cpus are brought online.

    Task finishes work and does sched_setaffinity(saved_mask).

    Task will never run on the new cpus.


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