On Sun, 2012-07-01 at 12:02 -0700, Hugh Dickins wrote:

On Sun, 1 Jul 2012, Ben Hutchings wrote:

quoted

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Konstantin Khlebnikov <redacted>

commit 4fe7efdbdfb1c7e7a7f31decfd831c0f31d37091 upstream.

do_exit() and exec_mmap() call sync_mm_rss() before mm_release() does
put_user(clear_child_tid) which can update task->rss_stat and thus make
mm->rss_stat inconsistent.  This triggers the "BUG:" printk in check_mm().

Let's fix this bug in the safest way, and optimize/cleanup this later.

Reported-by: Markus Trippelsdorf <redacted>
Signed-off-by: Konstantin Khlebnikov <redacted>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: KAMEZAWA Hiroyuki <redacted>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2: sync_mm_rss() still takes a struct task_struct *]
Signed-off-by: Ben Hutchings <redacted>

If you or Konstantin or Oleg have done full diligence on this,
to ensure that it is really applicable to 3.2 (not just that
the patch applies without rejects), fair enough.

I can't claim that, no.

But I'd be cautious about it: it went through enough alternatives
and revisions that I wouldn't call it trivial; it's easy for me to
imagine that some of the affected paths were actually slightly different
in 3.2 days than they were in 3.4 days; and the disturbing warning that
these mods silence ("BUG: Bad rss-counter state ") did not exist before
3.4 - unless you've ported that too?

No.

That's not to assert that we had no rss problem at all before 3.4,
but we've not heard of any trouble from it.  Caution tells me that
this patch might cause more trouble than it's worth.

Then I'll assume this should be dropped unless Konstantin or Oleg speaks
up for it.

Ben.

-- 
Ben Hutchings
When in doubt, use brute force. - Ken Thompson