[PATCH 1/2] correctly synchronize rss-counters at exit/exec

[Oleg Nesterov <oleg@redhat.com>]

A simplified version of Konstantin Khlebnikov's patch.

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().

- Move the final sync_mm_rss() from do_exit() to exit_mm(), and
  change exec_mmap() to call sync_mm_rss() after mm_release() to
  make check_mm() happy.

  Perhaps we should simply move it into mm_release() and call it
  unconditionally to catch the "task->rss_stat != 0 && !task->mm"
  bugs.

- Since taskstats_exit() is called before exit_mm(), add another
  sync_mm_rss() into xacct_add_tsk() who actually uses rss_stat.

  Probably we should also shift acct_update_integrals().

Reported-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Tested-by: Martin Mokrejs <mmokrejs@fold.natur.cuni.cz>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
---
 fs/exec.c       |    2 +-
 kernel/exit.c   |    5 ++---
 kernel/tsacct.c |    1 +
 3 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 52c9e2f..e49e3c2 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -823,10 +823,10 @@ 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 ab972a7..b3a84b5 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -655,6 +655,8 @@ 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
@@ -965,9 +967,6 @@ 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);
 	group_dead = atomic_dec_and_test(&tsk->signal->live);
 	if (group_dead) {
 		hrtimer_cancel(&tsk->signal->real_timer);
diff --git a/kernel/tsacct.c b/kernel/tsacct.c
index 23b4d78..a64ee90 100644
--- a/kernel/tsacct.c
+++ b/kernel/tsacct.c
@@ -91,6 +91,7 @@ void xacct_add_tsk(struct taskstats *stats, struct task_struct *p)
 	stats->virtmem = p->acct_vm_mem1 * PAGE_SIZE / MB;
 	mm = get_task_mm(p);
 	if (mm) {
+		sync_mm_rss(mm);
 		/* adjust to KB unit */
 		stats->hiwater_rss   = get_mm_hiwater_rss(mm) * PAGE_SIZE / KB;
 		stats->hiwater_vm    = get_mm_hiwater_vm(mm)  * PAGE_SIZE / KB;
-- 
1.5.5.1