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 <qiuxishi@xxxxxxxxxx> 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()
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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> .
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