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 <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()
Do you mean else if(is_free_buddy_page(p)) branch is redundancy?
>
> 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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