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    SubjectRe: Request for documentation of PID handling functions
    On 07/30, Pavel Emelyanov wrote:
    >
    > David Howells wrote:
    > > Hi Pavel,
    > >
    > > Can you please provide documentation for the PID handling functions you
    > > supplied in commit:
    > >
    > > 7af5729474b5b8ad385adadab78d6e723e7655a3
    > >
    > > In particular I'd like to know what locks are required when. I'm trying to
    > > determine if in this piece of code:
    > >
    > > read_lock(&tasklist_lock);
    > > ret = 0;
    > > if (pid != task_pid_vnr(current))
    > > ret = -EPERM;
    > > read_unlock(&tasklist_lock);
    > >
    > > the lock of tasklist_lock is necessary.
    >
    > The RCU protection is enough to get pids from tasks. However, the pids
    > are detached under the tasklist lock write-locked, so provided you're
    > *already* sitting under it the RCU is excessive.

    Yes, tasklist OR rcu is enough.

    But, since the task == current, the code above doesn't need any locks at all.

    Unless this code runs after exit_notify() of course, in that case we need
    rcu/tasklist and task_pid_vnr(current) can return 0.

    Oleg.



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