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    SubjectRe: [PATCH 1/1] V3: hotplug cpu: migrate a task within its cpuset
    On 08/27, Cliff Wickman wrote:
    >
    > --- linus.070821.orig/kernel/sched.c
    > +++ linus.070821/kernel/sched.c
    > @@ -61,6 +61,7 @@
    > #include <linux/delayacct.h>
    > #include <linux/reciprocal_div.h>
    > #include <linux/unistd.h>
    > +#include <linux/cpuset.h>
    >
    > #include <asm/tlb.h>
    >
    > @@ -5091,6 +5092,19 @@ restart:
    > if (dest_cpu == NR_CPUS)
    > dest_cpu = any_online_cpu(p->cpus_allowed);
    >
    > + /* try to stay on the same cpuset */
    > + if (dest_cpu == NR_CPUS) {
    > + rq = task_rq_lock(p, &flags);
    > + /*
    > + * The cpuset_cpus_allowed_locked() variant of
    > + * cpuset_cpus_allowed() will not block
    > + * It must be called within calls to cpuset_lock/cpuset_unlock.
    > + */
    > + p->cpus_allowed = cpuset_cpus_allowed_locked(p);
    > + dest_cpu = any_online_cpu(p->cpus_allowed);
    > + task_rq_unlock(rq, &flags);

    No, no, we can't take task_lock() under rq->lock, nesting error. I think we
    need a local "cpumask_t cpus_allowed = cpuset_cpus_allowed_locked()", like
    sched_setaffinity() does.

    task_lock() doesn't disable irqs, this means that it can't be used under any
    lock which can be used from interrupt context.

    Oleg.

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