From: Andrew Morton <akpm@linux-foundation.org>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: "\\\"Kirill A. Shutemov\\\"" <kirill@shutemov.name>,
linux-mm@kvack.org, stable@vger.kernel.org
Subject: Re: [PATCH 1/1] mm: thp: fix SMP race condition between THP page fault and MADV_DONTNEED
Date: Tue, 23 Feb 2016 13:18:44 -0800 [thread overview]
Message-ID: <20160223131844.d5d2767a0cc44bd8cbb78221@linux-foundation.org> (raw)
In-Reply-To: <1456253350-3959-2-git-send-email-aarcange@redhat.com>
On Tue, 23 Feb 2016 19:49:10 +0100 Andrea Arcangeli <aarcange@redhat.com> wrote:
> pmd_trans_unstable()/pmd_none_or_trans_huge_or_clear_bad() were
> introduced to locklessy (but atomically) detect when a pmd is a
> regular (stable) pmd or when the pmd is unstable and can infinitely
> transition from pmd_none() and pmd_trans_huge() from under us, while
> only holding the mmap_sem for reading (for writing not).
>
> While holding the mmap_sem only for reading, MADV_DONTNEED can run
> from under us and so before we can assume the pmd to be a regular
> stable pmd we need to compare it against pmd_none() and
> pmd_trans_huge() in an atomic way, with pmd_trans_unstable(). The old
> pmd_trans_huge() left a tiny window for a race.
>
> Useful applications are unlikely to notice the difference as doing
> MADV_DONTNEED concurrently with a page fault would lead to undefined
> behavior.
Thanks.
I put a cc:stable on this as it appears to be applicable to 4.4 and
perhaps earlier.
It generates a reject against 4.4 because of the recently-added
pmd_devmap() test. It's easily fixed but I don't have a process to
handle -stable rejects. This means that when Greg hits the reject
he'll ask us for a fixed up version.
--
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>
prev parent reply other threads:[~2016-02-23 21:18 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-23 15:49 THP race? Kirill A. Shutemov
2016-02-23 18:06 ` Andrea Arcangeli
2016-02-23 18:18 ` [PATCH 1/1] mm: thp: fix SMP race condition between THP page fault kbuild test robot
2016-02-23 18:21 ` kbuild test robot
2016-02-23 18:27 ` kbuild test robot
2016-02-23 18:38 ` THP race? Kirill A. Shutemov
2016-02-23 19:28 ` Andrea Arcangeli
2016-02-25 18:45 ` Dan Williams
2016-02-26 10:37 ` Kirill A. Shutemov
2016-02-26 14:46 ` Dan Williams
2016-02-23 18:49 ` [PATCH 0/1] " Andrea Arcangeli
2016-02-23 18:49 ` [PATCH 1/1] mm: thp: fix SMP race condition between THP page fault and MADV_DONTNEED Andrea Arcangeli
2016-02-23 21:18 ` Andrew Morton [this message]
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=20160223131844.d5d2767a0cc44bd8cbb78221@linux-foundation.org \
--to=akpm@linux-foundation.org \
--cc=aarcange@redhat.com \
--cc=kirill@shutemov.name \
--cc=linux-mm@kvack.org \
--cc=stable@vger.kernel.org \
/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).