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    SubjectRe: [PATCH] exit: fix oops in sync_mm_rss
    On Wed, 31 Mar 2010 09:28:15 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

    > On Tue, 30 Mar 2010 13:56:34 -0700
    > Andrew Morton <akpm@linux-foundation.org> wrote:
    >
    > > That new BUG_ON() is triggering in Troels's machine when a bluetooth
    > > keyboard is enabled or disabled. See
    > > (https://bugzilla.kernel.org/show_bug.cgi?id=15648.
    > >
    > > I guess the question is: how did a kernel thread get a non-zero
    > > task->rss_stat.count[i]? If that's expected and OK then we will need
    > > to take some kernel-thread-avoidance action there.
    > >
    > It seems my fault that it's not initialized to be 0 at do_fork(), copy_process.
    >
    > About do_exit, do_exit() does this check. So, tsk->mm can be NULL.
    >
    > 949 if (group_dead) {
    > 950 hrtimer_cancel(&tsk->signal->real_timer);
    > 951 exit_itimers(tsk->signal);
    > 952 if (tsk->mm)
    > 953 setmax_mm_hiwater_rss(&tsk->signal->maxrss, tsk->mm);
    > 954 }
    >
    > > Could whoever fixes this please also make __sync_task_rss_stat()
    > > static.
    > >
    > Ah, yes. I should do so.
    >
    > > I'll toss this over to Rafael/Maciej for tracking as a post-2.6.33
    > > regression.
    > >
    > > Thanks.
    > >
    >
    >
    > ==
    >
    > task->rss_stat wasn't initialized to 0 at copy_process().
    > at exit, tsk->mm may be NULL.
    > And __sync_task_rss_stat() should be static.
    >
    > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > ---
    > kernel/exit.c | 3 ++-
    > kernel/fork.c | 3 +++
    > mm/memory.c | 2 +-
    > 3 files changed, 6 insertions(+), 2 deletions(-)
    >
    > Index: mmotm-2.6.34-Mar24/kernel/exit.c
    > ===================================================================
    > --- mmotm-2.6.34-Mar24.orig/kernel/exit.c
    > +++ mmotm-2.6.34-Mar24/kernel/exit.c
    > @@ -950,7 +950,8 @@ NORET_TYPE void do_exit(long code)
    >
    > acct_update_integrals(tsk);
    > /* sync mm's RSS info before statistics gathering */
    > - sync_mm_rss(tsk, tsk->mm);
    > + if (tsk->mm)
    > + sync_mm_rss(tsk, tsk->mm);
    > group_dead = atomic_dec_and_test(&tsk->signal->live);
    > if (group_dead) {
    > hrtimer_cancel(&tsk->signal->real_timer);
    > Index: mmotm-2.6.34-Mar24/mm/memory.c
    > ===================================================================
    > --- mmotm-2.6.34-Mar24.orig/mm/memory.c
    > +++ mmotm-2.6.34-Mar24/mm/memory.c
    > @@ -124,7 +124,7 @@ core_initcall(init_zero_pfn);
    >
    > #if defined(SPLIT_RSS_COUNTING)
    >
    > -void __sync_task_rss_stat(struct task_struct *task, struct mm_struct *mm)
    > +static void __sync_task_rss_stat(struct task_struct *task, struct mm_struct *mm)
    > {
    > int i;
    >
    > Index: mmotm-2.6.34-Mar24/kernel/fork.c
    > ===================================================================
    > --- mmotm-2.6.34-Mar24.orig/kernel/fork.c
    > +++ mmotm-2.6.34-Mar24/kernel/fork.c
    > @@ -1060,6 +1060,9 @@ static struct task_struct *copy_process(
    > p->prev_utime = cputime_zero;
    > p->prev_stime = cputime_zero;
    > #endif
    > +#if defined(SPLIT_RSS_COUNTING)
    > + memset(&p->rss_stat, 0, sizeof(p->rss_stat));
    > +#endif
    >
    > p->default_timer_slack_ns = current->timer_slack_ns;

    OK, so the kenrel thread inherited a non-zero rss_stat from a userspace
    parent?

    With this fixed, the test for non-zero tsk->mm is't really needed in
    do_exit(), is it? I guess it makes sense though - sync_mm_rss() only
    really works for kernel threads by luck..


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