Re: [BUG] memcg: panic when rmdir()

[Li Zefan <lizf@cn.fujitsu.com>]

KAMEZAWA Hiroyuki wrote:
> On Fri, 16 Jan 2009 14:15:04 +0800
> Li Zefan <lizf@cn.fujitsu.com> wrote:
> 
>> Found this when testing memory resource controller, can be triggered
>> with:
>> - CONFIG_CGROUP_MEM_RES_CTLR_SWAP=n
>> - or CONFIG_CGROUP_MEM_RES_CTLR_SWAP=y
>> - or CONFIG_CGROUP_MEM_RES_CTLR_SWAP=y && boot with noswapaccount
>>
> 
> Li-san, could you try this ? I myself can't reproduce the bug yet...

I've tested this patch, and the bug seems to disappear. :)

Tested-by: Li Zefan <lizf@cn.fujitsu.com>

I'm going to be off office, and I'll do more testing to confirm this
next week.

> ==
> 
> 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.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> ---
> 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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