Revert "mm: correctly synchronize rss-counters at exit/exec"

This reverts commit 40af1bbdca47e5c8a2044039bb78ca8fd8b20f94.

It's horribly and utterly broken for at least the following reasons:

 - calling sync_mm_rss() from mmput() is fundamentally wrong, because
   there's absolutely no reason to believe that the task that does the
   mmput() always does it on its own VM.  Example: fork, ptrace, /proc -
   you name it.

 - calling it *after* having done mmdrop() on it is doubly insane, since
   the mm struct may well be gone now.

 - testing mm against NULL before you call it is insane too, since a
NULL mm there would have caused oopses long before.

.. and those are just the three bugs I found before I decided to give up
looking for me and revert it asap.  I should have caught it before I
even took it, but I trusted Andrew too much.

Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 8 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 804fb6bb8161..34867cc5b42a 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -423,7 +423,6 @@ 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
@@ -641,6 +640,7 @@ 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;
         /*
@@ -960,13 +960,9 @@ void do_exit(long code)
                                 preempt_count());
 
         acct_update_integrals(tsk);
-
-        /* 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);
-
+        /* sync mm's RSS info before statistics gathering */
+        if (tsk->mm)
+                sync_mm_rss(tsk->mm);
         group_dead = atomic_dec_and_test(&tsk->signal->live);
         if (group_dead) {
                 hrtimer_cancel(&tsk->signal->real_timer);
@@ -979,6 +975,7 @@ void do_exit(long code)
                 tty_audit_exit();
         audit_free(tsk);
 
+        tsk->exit_code = code;
         taskstats_exit(tsk, group_dead);
 
         exit_mm(tsk);