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    SubjectRe: 2.6.26-rc4: RIP find_pid_ns+0x6b/0xa0
    On 05/27, Oleg Nesterov wrote:
    >
    > But I agree, this race is pretty much theoretical.

    Perhaps we have the unbalanced put_pid(), in that case "struct pid" will
    be freed without waiting for a grace period.

    Alexey, could you re-test with the patch below?

    Oleg.

    Add the temporary debugging code to catch the unbalanced put_pid()'s.
    At least those which can free the "live" pid.

    --- MM/kernel/pid.c~ 2008-02-20 18:29:40.000000000 +0300
    +++ MM/kernel/pid.c 2008-02-20 18:35:15.000000000 +0300
    @@ -208,6 +208,10 @@ void put_pid(struct pid *pid)
    ns = pid->numbers[pid->level].ns;
    if ((atomic_read(&pid->count) == 1) ||
    atomic_dec_and_test(&pid->count)) {
    + int type = PIDTYPE_MAX;
    + while (--type >= 0)
    + if (WARN_ON(!hlist_empty(&pid->tasks[type])))
    + return;
    kmem_cache_free(ns->pid_cachep, pid);
    put_pid_ns(ns);
    }



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