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    SubjectRe: [PATCH -mm 2/4] oom: select_bad_process: PF_EXITING check should take ->mm into account
    On Fri, Apr 02, 2010 at 08:32:16PM +0200, Oleg Nesterov 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.
    >
    > Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    > ---
    >
    > mm/oom_kill.c | 2 +-
    > 1 file changed, 1 insertion(+), 1 deletion(-)
    >
    > --- MM/mm/oom_kill.c~2_FIX_PF_EXITING 2010-04-02 18:51:05.000000000 +0200
    > +++ MM/mm/oom_kill.c 2010-04-02 18:58:37.000000000 +0200
    > @@ -322,7 +322,7 @@ static struct task_struct *select_bad_pr
    > * 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) {

    Even this check is satisfied, it still can't say p is a good victim or
    it will release memory automatically if multi threaded, as the exiting
    of p doesn't mean the other threads are going to exit, so the ->mm won't
    be released.

    > if (p != current)
    > return ERR_PTR(-1UL);
    >
    >


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