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mm: correctly synchronize rss-counters at exit/exec

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mm->rss_stat counters have per-task delta: task->rss_stat.  Before
changing task->mm pointer the kernel must flush this delta with
sync_mm_rss().

do_exit() already calls sync_mm_rss() to flush the rss-counters before
committing the rss statistics into task->signal->maxrss, taskstats,
audit and other stuff.  Unfortunately the kernel does this before
calling mm_release(), which can call put_user() for processing
task->clear_child_tid.  So at this point we can trigger page-faults and
task->rss_stat becomes non-zero again.  As a result mm->rss_stat becomes
inconsistent and check_mm() will print something like this:

| BUG: Bad rss-counter state mm:ffff88020813c380 idx:1 val:-1
| BUG: Bad rss-counter state mm:ffff88020813c380 idx:2 val:1

This patch moves sync_mm_rss() into mm_release(), and moves mm_release()
out of do_exit() and calls it earlier.  After mm_release() there should
be no pagefaults.

[akpm@linux-foundation.org: tweak comment]
Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Reported-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: <stable@vger.kernel.org>		[3.4.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Konstantin Khlebnikov 2012-06-07 14:21:14 -07:00 committed by Linus Torvalds
parent 39caa0916e
commit 40af1bbdca
3 changed files with 16 additions and 6 deletions
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1
fs/exec.c
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@ -819,7 +819,6 @@ static int exec_mmap(struct mm_struct *mm)
/* Notify parent that we're no longer interested in the old VM */
tsk = current;
old_mm = current->mm;
sync_mm_rss(old_mm);
mm_release(tsk, old_mm);
if (old_mm) {

13
kernel/exit.c
View file

@ -423,6 +423,7 @@ void daemonize(const char *name, ...)
* user space pages. We don't need them, and if we didn't close them
* they would be locked into memory.
*/
mm_release(current, current->mm);
exit_mm(current);
/*
* We don't want to get frozen, in case system-wide hibernation
@ -640,7 +641,6 @@ static void exit_mm(struct task_struct * tsk)
struct mm_struct *mm = tsk->mm;
struct core_state *core_state;
mm_release(tsk, mm);
if (!mm)
return;
/*
@ -960,9 +960,13 @@ void do_exit(long code)
preempt_count());
acct_update_integrals(tsk);
/* sync mm's RSS info before statistics gathering */
if (tsk->mm)
sync_mm_rss(tsk->mm);
/* Set exit_code before complete_vfork_done() in mm_release() */
tsk->exit_code = code;
/* Release mm and sync mm's RSS info before statistics gathering */
mm_release(tsk, tsk->mm);
group_dead = atomic_dec_and_test(&tsk->signal->live);
if (group_dead) {
hrtimer_cancel(&tsk->signal->real_timer);
@ -975,7 +979,6 @@ void do_exit(long code)
tty_audit_exit();
audit_free(tsk);
tsk->exit_code = code;
taskstats_exit(tsk, group_dead);
exit_mm(tsk);

8
kernel/fork.c
View file

@ -619,6 +619,14 @@ void mmput(struct mm_struct *mm)
module_put(mm->binfmt->module);
mmdrop(mm);
}
/*
* Final rss-counter synchronization. After this point there must be
* no pagefaults into this mm from the current context. Otherwise
* mm->rss_stat will be inconsistent.
*/
if (mm)
sync_mm_rss(mm);
}
EXPORT_SYMBOL_GPL(mmput);