Re: [PATCH] hugetlbfs: don't delete error page from pagecache

From: Mike Kravetz <mike.kravetz@oracle.com>
To: "HORIGUCHI NAOYA(堀口　直也)" <naoya.horiguchi@nec.com>
Cc: James Houghton <jthoughton@google.com>,
	Muchun Song <songmuchun@bytedance.com>,
	Miaohe Lin <linmiaohe@huawei.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Yang Shi <shy828301@gmail.com>,
	Axel Rasmussen <axelrasmussen@google.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] hugetlbfs: don't delete error page from pagecache
Date: Fri, 4 Nov 2022 06:27:44 -0700	[thread overview]
Message-ID: <Y2UTUNBHVY5U9si2@monkey> (raw)
In-Reply-To: <20221104021035.GA297167@hori.linux.bs1.fc.nec.co.jp>

On 11/04/22 02:10, HORIGUCHI NAOYA(堀口 直也) wrote:
> On Tue, Oct 18, 2022 at 08:01:25PM +0000, James Houghton wrote:
> > This change is very similar to the change that was made for shmem [1],
> > and it solves the same problem but for HugeTLBFS instead.
> > 
> > Currently, when poison is found in a HugeTLB page, the page is removed
> > from the page cache. That means that attempting to map or read that
> > hugepage in the future will result in a new hugepage being allocated
> > instead of notifying the user that the page was poisoned. As [1] states,
> > this is effectively memory corruption.
> > 
> > The fix is to leave the page in the page cache. If the user attempts to
> > use a poisoned HugeTLB page with a syscall, the syscall will fail with
> > EIO, the same error code that shmem uses. For attempts to map the page,
> > the thread will get a BUS_MCEERR_AR SIGBUS.
> > 
> > [1]: commit a76054266661 ("mm: shmem: don't truncate page if memory failure happens")
> > 
> > Signed-off-by: James Houghton <jthoughton@google.com>
> 
> I did some testing and found no issue. So I agree with this patch.
> Thank you very much.
> 
> Tested-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
> Reviewed-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
> 
> As for whether to go with HGM patchset or not, I have no strong opinion.
> As you stated in another email this patch is correct without HGM patch,
> so it's OK to me to make this merged first.

Thanks Naoya.

This is a late thought, but ...
Should this patch and Yang Shi's shmem patch be backported to stable releases?
Both address potential data corruption/loss, so it certainly seems like
stable material.
-- 
Mike Kravetz