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Subject[PATCH] mm: correctly synchronize rss-counters at exit/exec
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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>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
---
fs/exec.c | 2 +-
kernel/exit.c | 1 +
2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/exec.c b/fs/exec.c
index a79786a..da27b91 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 34867cc..c0277d3 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


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