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    SubjectRe: [ 11/48] mm: correctly synchronize rss-counters at exit/exec
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    On Sun, 2012-07-01 at 12:02 -0700, Hugh Dickins wrote:
    > On Sun, 1 Jul 2012, Ben Hutchings wrote:
    >
    > > 3.2-stable review patch. If anyone has any objections, please let me know.
    > >
    > > ------------------
    > >
    > > From: Konstantin Khlebnikov <khlebnikov@openvz.org>
    > >
    > > 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 <markus@trippelsdorf.de>
    > > Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
    > > Cc: Oleg Nesterov <oleg@redhat.com>
    > > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    > > 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 <ben@decadent.org.uk>
    >
    > 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
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