mm: correctly synchronize rss-counters at exit/exec

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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 2 insertions, 1 deletions

diff --git a/fs/exec.c b/fs/exec.c
index a79786a8d2c8..da27b91ff1e8 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -819,10 +819,10 @@ 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) {
+                sync_mm_rss(old_mm);
                 /*
                  * Make sure that if there is a core dump in progress
                  * for the old mm, we get out and die instead of going
diff --git a/kernel/exit.c b/kernel/exit.c
index 34867cc5b42a..c0277d3f1aaa 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -643,6 +643,7 @@ static void exit_mm(struct task_struct * tsk)
         mm_release(tsk, mm);
         if (!mm)
                 return;
+        sync_mm_rss(mm);
         /*
          * Serialize with any possible pending coredump.
          * We must hold mmap_sem around checking core_state