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    Subject[RFC] [PATCH 1/3] task_cpu(p) needs to be correct always
    We rely very much on task_cpu(p) to be correct at all times, so that we can
    correctly find the task_grp_rq from which the task has to be removed or added
    to.

    There is however one place in the scheduler where this assumption of
    task_cpu(p) being correct is broken. This patch fixes that piece of code.

    (Thanks to Balbir Singh for pointing this out to me)

    Signed-off-by : Srivatsa Vaddagiri <vatsa@in.ibm.com>

    ---
    kernel/sched.c | 8 +++++---
    1 file changed, 5 insertions(+), 3 deletions(-)

    Index: linux-2.6.21-rc7/kernel/sched.c
    ===================================================================
    --- linux-2.6.21-rc7.orig/kernel/sched.c 2007-05-23 20:46:41.000000000 +0530
    +++ linux-2.6.21-rc7/kernel/sched.c 2007-05-23 20:48:26.000000000 +0530
    @@ -4571,7 +4571,7 @@
    static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
    {
    struct rq *rq_dest, *rq_src;
    - int ret = 0;
    + int ret = 0, on_rq;

    if (unlikely(cpu_is_offline(dest_cpu)))
    return ret;
    @@ -4587,9 +4587,11 @@
    if (!cpu_isset(dest_cpu, p->cpus_allowed))
    goto out;

    - set_task_cpu(p, dest_cpu);
    - if (p->on_rq) {
    + on_rq = p->on_rq;
    + if (on_rq)
    deactivate_task(rq_src, p, 0);
    + set_task_cpu(p, dest_cpu);
    + if (on_rq) {
    activate_task(rq_dest, p, 0);
    check_preempt_curr(rq_dest, p);
    }
    --
    Regards,
    vatsa
    -
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