[BUGFIX] [PATCH] memcg: fix refcnt handling at swapoff

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Fri, 16 Jan 2009 18:12:35 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> How-to-reproduce.
> 
> In shell-A
>   #mount -t cgroup none /opt/cgroup
>   #mkdir /opt/cgroup/xxx/
>   #echo 0 > /opt/cgroup/xxx/tasks
>   #Run malloc 100M on this and sleep. ---(*)
> 
> In shell-B.
>   #echo 40M > /opt/cgroup/xxx/memory.limit_in_bytes.
>   Then, you'll see 60M of swap.
>   #/sbin/swapoff -a 
>   Then, you'll see OOM-Kill against (*)
>   #echo shell-A > /opt/cgroup/tasks
>   make /opt/cgroup/xxx/ empty
>   #rmdir /opt/cgroup/xxx
> 
> => panics.
> 
I'll update how-to-test text under Documentation/ later.
-Kame
==
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Now, at swapoff, even while try_charge() fails, commit is executed.
This is bug and make refcnt of cgroup_subsys_state minus, finally.

Reported-by: Li Zefan <lizf@cn.fujitsu.com>
Tested-by: Li Zefan <lizf@cn.fujitsu.com>
Tested-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
---
 mm/swapfile.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Index: mmotm-2.6.29-Jan14/mm/swapfile.c
===================================================================
--- mmotm-2.6.29-Jan14.orig/mm/swapfile.c
+++ mmotm-2.6.29-Jan14/mm/swapfile.c
@@ -698,8 +698,10 @@ static int unuse_pte(struct vm_area_stru
 	pte_t *pte;
 	int ret = 1;
 
-	if (mem_cgroup_try_charge_swapin(vma->vm_mm, page, GFP_KERNEL, &ptr))
+	if (mem_cgroup_try_charge_swapin(vma->vm_mm, page, GFP_KERNEL, &ptr)) {
 		ret = -ENOMEM;
+		goto out_nolock;
+	}
 
 	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
 	if (unlikely(!pte_same(*pte, swp_entry_to_pte(entry)))) {
@@ -723,6 +725,7 @@ static int unuse_pte(struct vm_area_stru
 	activate_page(page);
 out:
 	pte_unmap_unlock(pte, ptl);
+out_nolock:
 	return ret;
 }
 

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