On Mon, Aug 10, 2015 at 04:29:18PM +0800, Wanpeng Li wrote:
> Hi Naoya,
>
> On 8/10/15 4:10 PM, Naoya Horiguchi wrote:
> >On Mon, Aug 10, 2015 at 02:32:30PM +0800, Wanpeng Li wrote:
> >>THP pages will get a refcount in madvise_hwpoison() w/ MF_COUNT_INCREASED
> >>flag, however, the refcount is still held when fail to split THP pages.
> >>
> >>Fix it by reducing the refcount of THP pages when fail to split THP.
> >>
> >>Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> >It seems that the same conditional put_page() would be added to
> >"soft offline: %#lx page already poisoned" branch too, right?
>
> PageHWPoison() is just called before the soft_offline_page() in
> madvise_hwpoion(). I think the PageHWPosion()
> check in soft_offline_page() makes more sense for the other
> soft_offline_page() callsites which don't have the
> refcount held.
What I am worried is a race like below:
CPU0 CPU1
madvise_hwpoison
get_user_pages_fast
PageHWPoison check (false)
memory_failure
TestSetPageHWPoison
soft_offline_page
PageHWPoison check (true)
return -EBUSY (without put_page)
It's rare and madvise_hwpoison() is testing feature, so this never causes
real problems in production systems, so it's not a big deal.
My suggestion is maybe just for code correctness thing ...
Thanks,
Naoya Horiguchi
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