On 2012/12/10 18:47, Simon Jeons wrote:
> On Mon, 2012-12-10 at 17:06 +0800, Xishi Qiu wrote:
>> On 2012/12/10 16:33, Wanpeng Li wrote:
>>
>>> On Fri, Dec 07, 2012 at 02:11:02PM -0800, Andrew Morton wrote:
>>>> On Fri, 7 Dec 2012 16:48:45 +0800
>>>> Xishi Qiu <qiuxi...@huawei.com> wrote:
>>>>
>>>>> On x86 platform, if we use "/sys/devices/system/memory/soft_offline_page"
>>>>> to offline a
>>>>> free page twice, the value of mce_bad_pages will be added twice. So this
>>>>> is an error,
>>>>> since the page was already marked HWPoison, we should skip the page and
>>>>> don't add the
>>>>> value of mce_bad_pages.
>>>>>
>>>>> $ cat /proc/meminfo | grep HardwareCorrupted
>>>>>
>>>>> soft_offline_page()
>>>>> get_any_page()
>>>>> atomic_long_add(1, &mce_bad_pages)
>>>>>
>>>>> ...
>>>>>
>>>>> --- a/mm/memory-failure.c
>>>>> +++ b/mm/memory-failure.c
>>>>> @@ -1582,8 +1582,11 @@ int soft_offline_page(struct page *page, int flags)
>>>>> return ret;
>>>>>
>>>>> done:
>>>>> - atomic_long_add(1, &mce_bad_pages);
>>>>> - SetPageHWPoison(page);
>>>>> /* keep elevated page count for bad page */
>>>>> + if (!PageHWPoison(page)) {
>>>>> + atomic_long_add(1, &mce_bad_pages);
>>>>> + SetPageHWPoison(page);
>>>>> + }
>>>>> +
>>>>> return ret;
>>>>> }
>>>>
>>>> A few things:
>>>>
>>>> - soft_offline_page() already checks for this case:
>>>>
>>>> if (PageHWPoison(page)) {
>>>> unlock_page(page);
>>>> put_page(page);
>>>> pr_info("soft offline: %#lx page already poisoned\n", pfn);
>>>> return -EBUSY;
>>>> }
>>>>
>>>> so why didn't this check work for you?
>>>>
>>>> Presumably because one of the earlier "goto done" branches was
>>>> taken. Which one, any why?
>>>>
>>>> This function is an utter mess. It contains six return points
>>>> randomly intermingled with three "goto done" return points.
>>>>
>>>> This mess is probably the cause of the bug you have observed. Can
>>>> we please fix it up somehow? It *seems* that the design (lol) of
>>>> this function is "for errors, return immediately. For success, goto
>>>> done". In which case "done" should have been called "success". But
>>>> if you just look at the function you'll see that this approach didn't
>>>> work. I suggest it be converted to have two return points - one for
>>>> the success path, one for the failure path. Or something.
>>>>
>>>> - soft_offline_huge_page() is a miniature copy of soft_offline_page()
>>>> and might suffer the same bug.
>>>>
>>>> - A cleaner, shorter and possibly faster implementation is
>>>>
>>>> if (!TestSetPageHWPoison(page))
>>>> atomic_long_add(1, &mce_bad_pages);
>>>>
>>>
>>> Hi Andrew,
>>>
>>> Since hwpoison bit for free buddy page has already be set in get_any_page,
>>> !TestSetPageHWPoison(page) will not increase mce_bad_pages count even for
>>> the first time.
>>>
>>> Regards,
>>> Wanpeng Li
>>>
>>
>> The poisoned page is isolated in bad_page(), I wonder whether it could be
>> isolated
>> immediately in soft_offline_page() and memory_failure()?
>>
>> buffered_rmqueue()
>> prep_new_page()
>> check_new_page()
>> bad_page()
>
> Do you mean else if(is_free_buddy_page(p)) branch is redundancy?
>
Hi Simon,
get_any_page() -> "else if(is_free_buddy_page(p))" branch is *not* redundancy.
It is another topic, I mean since the page is poisoned, so why not isolate it
from page buddy alocator in soft_offline_page() rather than in check_new_page().
I find soft_offline_page() only migrate the page and mark HWPoison, the poisoned
page is still managed by page buddy alocator.
>>
>> Thanks
>> Xishi Qiu
>>
>>>> - We have atomic_long_inc(). Use it?
>>>>
>>>> - Why do we have a variable called "mce_bad_pages"? MCE is an x86
>>>> concept, and this code is in mm/. Lights are flashing, bells are
>>>> ringing and a loudspeaker is blaring "layering violation" at us!
>>>>
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