From: Michal Hocko <mhocko@kernel.org>
To: akpm@linux-foundation.org
Cc: zhongjiang@huawei.com, qiuxishi@huawei.com, vbabka@suse.cz,
mm-commits@vger.kernel.org,
Mike Kravetz <mike.kravetz@oracle.com>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
Mel Gorman <mgorman@suse.de>,
linux-mm@kvack.org
Subject: Re: + mm-hugetlb-fix-race-when-migrate-pages.patch added to -mm tree
Date: Fri, 29 Jul 2016 13:27:07 +0200 [thread overview]
Message-ID: <20160729112707.GB8031@dhcp22.suse.cz> (raw)
In-Reply-To: <20160721074340.GA26398@dhcp22.suse.cz>
On Thu 21-07-16 09:43:40, Michal Hocko wrote:
> We have further discussed the patch and I believe it is not correct. See [1].
> I am proposing the following alternative.
Andrew, please drop the mm-hugetlb-fix-race-when-migrate-pages.patch. It
is clearly racy. Whether the BUG_ON update is really the right and
sufficient fix is not 100% clear yet and we are waiting for Zhong Jiang
testing.
> [1] http://lkml.kernel.org/r/20160720132431.GM11249@dhcp22.suse.cz
> ---
> From b1e9b3214f1859fdf7d134cdcb56f5871933539c Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@suse.com>
> Date: Thu, 21 Jul 2016 09:28:13 +0200
> Subject: [PATCH] mm, hugetlb: fix huge_pte_alloc BUG_ON
>
> Zhong Jiang has reported a BUG_ON from huge_pte_alloc hitting when he
> runs his database load with memory online and offline running in
> parallel. The reason is that huge_pmd_share might detect a shared pmd
> which is currently migrated and so it has migration pte which is
> !pte_huge.
>
> There doesn't seem to be any easy way to prevent from the race and in
> fact seeing the migration swap entry is not harmful. Both callers of
> huge_pte_alloc are prepared to handle them. copy_hugetlb_page_range
> will copy the swap entry and make it COW if needed. hugetlb_fault will
> back off and so the page fault is retries if the page is still under
> migration and waits for its completion in hugetlb_fault.
>
> That means that the BUG_ON is wrong and we should update it. Let's
> simply check that all present ptes are pte_huge instead.
>
> Reported-by: zhongjiang <zhongjiang@huawei.com>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> ---
> mm/hugetlb.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 34379d653aa3..31dd2b8b86b3 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4303,7 +4303,7 @@ pte_t *huge_pte_alloc(struct mm_struct *mm,
> pte = (pte_t *)pmd_alloc(mm, pud, addr);
> }
> }
> - BUG_ON(pte && !pte_none(*pte) && !pte_huge(*pte));
> + BUG_ON(pte && pte_present(*pte) && !pte_huge(*pte));
>
> return pte;
> }
> --
> 2.8.1
>
> --
> Michal Hocko
> SUSE Labs
--
Michal Hocko
SUSE Labs
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2016-07-29 11:27 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <578eb28b.YbRUDGz5RloTVlrE%akpm@linux-foundation.org>
2016-07-21 7:43 ` + mm-hugetlb-fix-race-when-migrate-pages.patch added to -mm tree Michal Hocko
2016-07-21 8:13 ` Naoya Horiguchi
2016-07-21 10:29 ` Michal Hocko
2016-07-21 10:54 ` zhong jiang
2016-07-21 11:27 ` Michal Hocko
2016-07-21 12:14 ` zhong jiang
2016-07-21 12:30 ` Michal Hocko
2016-07-21 12:45 ` zhong jiang
2016-07-21 12:55 ` Michal Hocko
2016-07-21 13:25 ` zhong jiang
2016-07-21 13:40 ` Michal Hocko
2016-07-21 13:58 ` zhong jiang
2016-07-21 14:01 ` Michal Hocko
2016-07-21 14:13 ` zhong jiang
2016-07-21 14:27 ` Michal Hocko
2016-07-21 14:33 ` zhong jiang
2016-07-22 7:17 ` Naoya Horiguchi
2016-07-26 7:58 ` Michal Hocko
2016-07-26 14:04 ` zhong jiang
2016-07-27 14:44 ` Michal Hocko
2016-07-29 11:27 ` Michal Hocko [this message]
2016-07-30 6:33 ` zhong jiang
2016-08-01 11:02 ` Michal Hocko
2016-08-01 15:04 ` zhong jiang
2016-08-01 15:31 ` Michal Hocko
[not found] <003701d1e328$202ca9d0$6085fd70$@alibaba-inc.com>
2016-07-21 8:19 ` Hillf Danton
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20160729112707.GB8031@dhcp22.suse.cz \
--to=mhocko@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=linux-mm@kvack.org \
--cc=mgorman@suse.de \
--cc=mike.kravetz@oracle.com \
--cc=mm-commits@vger.kernel.org \
--cc=n-horiguchi@ah.jp.nec.com \
--cc=qiuxishi@huawei.com \
--cc=vbabka@suse.cz \
--cc=zhongjiang@huawei.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).