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SubjectRe: [PATCH] exit: fix oops in sync_mm_rss
On Tue, 30 Mar 2010 18:22:58 -0400
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Wed, 31 Mar 2010 09:41:24 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>
> > > 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 ?
>
> uh, not really ;)
>
>
> I think we should do this too:
>
> --- a/mm/memory.c~exit-fix-oops-in-sync_mm_rss-fix
> +++ a/mm/memory.c
> @@ -131,7 +131,6 @@ static void __sync_task_rss_stat(struct
>
> for (i = 0; i < NR_MM_COUNTERS; i++) {
> if (task->rss_stat.count[i]) {
> - BUG_ON(!mm);
> add_mm_counter(mm, i, task->rss_stat.count[i]);
> task->rss_stat.count[i] = 0;
> }
> _
>
> Because we just made sure it can't happen, and if it _does_ happen, the
> oops will tell us the samme thing that the BUG_ON() would have.
>

Hmm, then, finaly..
==

task->rss_stat wasn't initialized to 0 at copy_process().
And __sync_task_rss_stat() should be static.
removed BUG_ON(!mm) in __sync_task_rss_stat() for avoiding to show
wrong information to code readers. Anyway, if !mm && task->rss_stat
has some value, panic will happen.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
kernel/fork.c | 3 +++
mm/memory.c | 3 +--
2 files changed, 4 insertions(+), 2 deletions(-)
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
@@ -124,13 +124,12 @@ 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;

for (i = 0; i < NR_MM_COUNTERS; i++) {
if (task->rss_stat.count[i]) {
- BUG_ON(!mm);
add_mm_counter(mm, i, task->rss_stat.count[i]);
task->rss_stat.count[i] = 0;
}
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;









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