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    SubjectRe: [PATCH -mm] select_bad_process: cleanup 'releasing' check
    On Sun, Aug 27, 2006 at 10:25:38PM +0400, Oleg Nesterov wrote:
    > On top of "select_bad_process: kill a bogus PF_DEAD/TASK_DEAD check"
    >
    > No logic changes, but imho easier to read.
    >
    > Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
    >
    > --- 2.6.18-rc4/mm/oom_kill.c~ 2006-08-27 20:56:23.000000000 +0400
    > +++ 2.6.18-rc4/mm/oom_kill.c 2006-08-27 21:58:32.000000000 +0400
    > @@ -205,7 +205,6 @@ static struct task_struct *select_bad_pr
    > do_posix_clock_monotonic_gettime(&uptime);
    > do_each_thread(g, p) {
    > unsigned long points;
    > - int releasing;
    >
    > /*
    > * skip kernel threads and tasks which have already released
    > @@ -227,16 +226,15 @@ static struct task_struct *select_bad_pr
    > * the process of exiting and releasing its resources.
    > * Otherwise we could get an OOM deadlock.
    > */
    > - releasing = test_tsk_thread_flag(p, TIF_MEMDIE) ||
    > - p->flags & PF_EXITING;
    > - if (releasing) {
    > - if (p->flags & PF_EXITING && p == current) {
    > - chosen = p;
    > - *ppoints = ULONG_MAX;
    > - break;
    > - }
    > - return ERR_PTR(-1UL);
    > - }
    > + if ((p->flags & PF_EXITING) && p == current) {
    > + chosen = p;
    > + *ppoints = ULONG_MAX;
    > + break;
    > + }
    > + if ((p->flags & PF_EXITING) ||
    > + test_tsk_thread_flag(p, TIF_MEMDIE))
    > + return ERR_PTR(-1UL);
    > +

    Hmm, actually I think I spot a bug in the original logic: we don't want
    to have more than 1 task with TIF_MEMDIE at once, becaues that gives it
    access to memory reserves (but I saw it first in the new formulation, so
    maybe that does suggest it is more readable ;)

    What I think should be done is the check for TIF_MEMDIE (and return -1)
    first, and then the PF_EXITING test. At which point, if current is found to
    be exiting, it should be chosen but not break... that way a subsequent MEMDIE
    or EXITING task has the chance to trigger the -1 return.

    Anyway, if you don't want to do all that, I will when my hand gets better.
    Otherwise the 3 patches you sent look good, they could all have an

    Acked-by: Nick Piggin <npiggin@suse.de>

    Thanks,
    Nick
    -
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