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



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