From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Dan Williams <dan.j.williams@intel.com>,
Justin He <Justin.He@arm.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Jeff Moyer <jmoyer@redhat.com>
Subject: Re: [PATCH] mm: Avoid data corruption on CoW fault into PFN-mapped VMA
Date: Thu, 20 Feb 2020 15:06:21 +0300 [thread overview]
Message-ID: <20200220120621.m2mmgih6bdzoqbck@box> (raw)
In-Reply-To: <20200219132239.92a22479e4bff7ec73ae6bdb@linux-foundation.org>
On Wed, Feb 19, 2020 at 01:22:39PM -0800, Andrew Morton wrote:
> On Tue, 18 Feb 2020 18:41:51 +0300 "Kirill A. Shutemov" <kirill@shutemov.name> wrote:
>
> > Jeff Moyer has reported that one of xfstests triggers a warning when run
> > on DAX-enabled filesystem:
> >
> > WARNING: CPU: 76 PID: 51024 at mm/memory.c:2317 wp_page_copy+0xc40/0xd50
> > ...
> > wp_page_copy+0x98c/0xd50 (unreliable)
> > do_wp_page+0xd8/0xad0
> > __handle_mm_fault+0x748/0x1b90
> > handle_mm_fault+0x120/0x1f0
> > __do_page_fault+0x240/0xd70
> > do_page_fault+0x38/0xd0
> > handle_page_fault+0x10/0x30
> >
> > The warning happens on failed __copy_from_user_inatomic() which tries to
> > copy data into a CoW page.
> >
> > This happens because of race between MADV_DONTNEED and CoW page fault:
> >
> > CPU0 CPU1
> > handle_mm_fault()
> > do_wp_page()
> > wp_page_copy()
> > do_wp_page()
> > madvise(MADV_DONTNEED)
> > zap_page_range()
> > zap_pte_range()
> > ptep_get_and_clear_full()
> > <TLB flush>
> > __copy_from_user_inatomic()
> > sees empty PTE and fails
> > WARN_ON_ONCE(1)
> > clear_page()
> >
> > The solution is to re-try __copy_from_user_inatomic() under PTL after
> > checking that PTE is matches the orig_pte.
> >
> > The second copy attempt can still fail, like due to non-readable PTE,
> > but there's nothing reasonable we can do about, except clearing the CoW
> > page.
>
> You don't think this is worthy of a cc:stable?
Please, add it.
Although, if I read history correctly, it is 15 year old bug that nobody
noticed until we added WARN() there :/
--
Kirill A. Shutemov
prev parent reply other threads:[~2020-02-20 12:05 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-18 15:41 [PATCH] mm: Avoid data corruption on CoW fault into PFN-mapped VMA Kirill A. Shutemov
2020-02-19 21:22 ` Andrew Morton
2020-02-20 12:06 ` Kirill A. Shutemov [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=20200220120621.m2mmgih6bdzoqbck@box \
--to=kirill@shutemov.name \
--cc=Justin.He@arm.com \
--cc=akpm@linux-foundation.org \
--cc=dan.j.williams@intel.com \
--cc=jmoyer@redhat.com \
--cc=kirill.shutemov@linux.intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.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).