Re: [PATCH] mm/memory-failure: call shake_page() when error hits thp tail page

[Andrew Morton]

On Wed, 15 Apr 2015 07:25:46 +0000 Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> wrote:

> Currently memory_failure() calls shake_page() to sweep pages out from pcplists
> only when the victim page is 4kB LRU page or thp head page. But we should do
> this for a thp tail page too.
> Consider that a memory error hits a thp tail page whose head page is on a
> pcplist when memory_failure() runs. Then, the current kernel skips shake_pages()
> part, so hwpoison_user_mappings() returns without calling split_huge_page() nor
> try_to_unmap() because PageLRU of the thp head is still cleared due to the skip
> of shake_page().
> As a result, me_huge_page() runs for the thp, which is a broken behavior.
> 
> This patch fixes this problem by calling shake_page() for thp tail case.
> 
> Fixes: 385de35722c9 ("thp: allow a hwpoisoned head page to be put back to LRU")
> Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx  # v3.4+

What are the userspace-visible effects of the bug?  This info is needed
for backporting into -stable and other kernels, please.


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