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@xxxxxxxxxx>
> ---
>
> 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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