On Wed, Mar 31, 2010 at 9:41 AM, KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > On Tue, 30 Mar 2010 17:37:21 -0400 > Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > >> On Wed, 31 Mar 2010 09:28:15 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: >> >> > On Tue, 30 Mar 2010 13:56:34 -0700 >> > Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx> >> > --- >> > 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? >> > I think so. > >> 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.. > > At first, I considered so, too. But I changed my mind to show > "we know tsk->mm can be NULL here!" by code. > Because __sync_mm_rss_stat() has BUG_ON(!mm), the code reader will think > tsk->mm shouldn't be NULL always. > > Doesn't make sense ? > Nitpick. How about moving sync_mm_rss into after check !mm of exit_mm? -- Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
