linux-kernel - Re: [PATCH] mm/memory-failure: call shake

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Message-Id: <20150420143014.bd6c683d159758db1815799f@linux-foundation.org>
Date:	Mon, 20 Apr 2015 14:30:14 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc:	Dean Nelson <dnelson@...hat.com>, Andi Kleen <andi@...stfloor.org>,
	"Andrea Arcangeli" <aarcange@...hat.com>,
	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>,
	Jin Dongming <jin.dongming@...css.fujitsu.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/memory-failure: call shake_page() when error hits
 thp tail page

On Wed, 15 Apr 2015 07:25:46 +0000 Naoya Horiguchi <n-horiguchi@...jp.nec.com> 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@...jp.nec.com>
> Cc: stable@...r.kernel.org  # 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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