Li Zefan wrote:
> No need for VM_BUG_ON(pc), since 'pc' is the list entry. This should
> be VM_BUG_ON(page).
> 
> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

pc is of type page_cgroup and we use list_for_each_entry_safe_reverse. Not sure
why we can't bug on pc.



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	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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> Li Zefan wrote:
> > No need for VM_BUG_ON(pc), since 'pc' is the list entry. This should
> > be VM_BUG_ON(page).
> > 
> > Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> > Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> 
> pc is of type page_cgroup and we use list_for_each_entry_safe_reverse. Not sure
> why we can't bug on pc.

pc is dereferenced before this VM_BUG_ON.

YAMAMOTO Takashi

> 
> 
> 
> -- 
> 	Warm Regards,
> 	Balbir Singh
> 	Linux Technology Center
> 	IBM, ISTL
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YAMAMOTO Takashi wrote:
>> Li Zefan wrote:
>>> No need for VM_BUG_ON(pc), since 'pc' is the list entry. This should
>>> be VM_BUG_ON(page).
>>>
>>> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
>>> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>> pc is of type page_cgroup and we use list_for_each_entry_safe_reverse. Not sure
>> why we can't bug on pc.
> 
> pc is dereferenced before this VM_BUG_ON.
> 
> YAMAMOTO Takashi
> 

OK, so the VM_BUG_ON needs to move to an earlier location. Agreed.

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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Balbir Singh wrote:
> YAMAMOTO Takashi wrote:
>>> Li Zefan wrote:
>>>> No need for VM_BUG_ON(pc), since 'pc' is the list entry. This should
>>>> be VM_BUG_ON(page).
>>>>
>>>> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
>>>> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>>> pc is of type page_cgroup and we use list_for_each_entry_safe_reverse. Not sure
>>> why we can't bug on pc.
>> pc is dereferenced before this VM_BUG_ON.
>>
>> YAMAMOTO Takashi
>>
> 
> OK, so the VM_BUG_ON needs to move to an earlier location. Agreed.
> 

No, 'pc' has been dereferenced in list_for_each_entry_safe_reverse().


#define list_for_each_entry_safe_reverse(pos, n, head, member)		\
	for (pos = list_entry((head)->prev, typeof(*pos), member),	\
		n = list_entry(pos->member.prev, typeof(*pos), member);	\
                               ^^^^^^^^^^^
	     &pos->member != (head); 					\
              ^^^^^^^^^^^
	     pos = n, n = list_entry(n->member.prev, typeof(*n), member))

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