Li Zefan wrote:
> 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 <[EMAIL PROTECTED]>
>>>>> Acked-by: KAMEZAWA Hiroyuki <[EMAIL PROTECTED]>
>>>> 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))
>
Hmm.. We used to have a for loop with !list_empty() as a termination condition
and VM_BUG_ON(!pc) is a spill over. With the new loop, VM_BUG_ON(!pc) does not
make sense.
--
Warm Regards,
Balbir Singh
Linux Technology Center
IBM, ISTL
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