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    SubjectRe: [PATCH 2/5] oom: select_bad_process: PF_EXITING check should take ->mm into account
    Thanks a lot Kosaki for doing this!

    I still can't find the time to play with this code :/

    On 05/31, KOSAKI Motohiro wrote:
    > select_bad_process() checks PF_EXITING to detect the task which is going
    > to release its memory, but the logic is very wrong.
    > - a single process P with the dead group leader disables
    > select_bad_process() completely, it will always return
    > ERR_PTR() while P can live forever
    > - if the PF_EXITING task has already released its ->mm
    > it doesn't make sense to expect it is goiing to free
    > more memory (except task_struct/etc)
    > Change the code to ignore the PF_EXITING tasks without ->mm.
    > --- a/mm/oom_kill.c
    > +++ b/mm/oom_kill.c
    > @@ -287,7 +287,7 @@ static struct task_struct *select_bad_process(unsigned long *ppoints,
    > * the process of exiting and releasing its resources.
    > * Otherwise we could get an easy OOM deadlock.
    > */
    > - if (p->flags & PF_EXITING) {
    > + if ((p->flags & PF_EXITING) && p->mm) {

    (strictly speaking, this change is needed after 3/5 which removes the
    top-level "if (!p->mm)" check in select_bad_process).

    I'd like to add a note... with or without this, we have problems
    with the coredump. A thread participating in the coredumping
    (group-leader in this case) can have PF_EXITING && mm, but this doesn't
    mean it is going to exit soon, and the dumper can use a lot more memory.

    Otoh, if select_bad_process() chooses the thread which dumps the core,
    SIGKILL can't stop it. This should be fixed in do_coredump() paths, this
    is the long-standing problem.

    And, as it was already discussed, we only check the group-leader here.
    But I can't suggest something better.


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      Last update: 2010-05-31 18:57    [W:0.020 / U:72.564 seconds]
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