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>

diff --git a/fs/exec.c b/fs/exec.c
index a79786a8d2c88d5b6c580859ef12496f43b4b0f4..da27b91ff1e8cbe87d0fe42aa5d39513e6a9deeb 100644 (file)
--- 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 34867cc5b42a77f325c204bb2fd09e1fabe38955..c0277d3f1aaa09c3a3f6f25d82b410525c4ca22f 100644 (file)
--- 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