From: Matthew Wilcox <willy@infradead.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: John Hubbard <jhubbard@nvidia.com>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org, cai@lca.pw, rppt@linux.ibm.com,
vbabka@suse.cz, william.kucharski@oracle.com,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v2] mm, dump_page: do not crash with bad compound_mapcount()
Date: Fri, 7 Aug 2020 16:10:29 +0100 [thread overview]
Message-ID: <20200807151029.GE17456@casper.infradead.org> (raw)
In-Reply-To: <20200807143504.4kudtd4xeoqaroqg@box>
On Fri, Aug 07, 2020 at 05:35:04PM +0300, Kirill A. Shutemov wrote:
> On Tue, Aug 04, 2020 at 02:48:07PM -0700, John Hubbard wrote:
> > If a compound page is being split while dump_page() is being run on that
> > page, we can end up calling compound_mapcount() on a page that is no
> > longer compound. This leads to a crash (already seen at least once in
> > the field), due to the VM_BUG_ON_PAGE() assertion inside
> > compound_mapcount().
[...]
> > +static inline int head_mapcount(struct page *head)
> > +{
>
> Do we want VM_BUG_ON_PAGE(!PageHead(head), head) here?
Well, no. That was the point of the bug report -- by the time we called
compound_mapcount, the page was no longer a head page.
> > A similar problem is possible, via compound_pincount() instead of
> > compound_mapcount().
> >
> > In order to avoid this kind of crash, make dump_page() slightly more
> > robust, by providing a pair of simpler routines that don't contain
> > assertions: head_mapcount() and head_pincount().
>
> I find naming misleading. head_mapcount() and head_pincount() sounds like
> a mapcount/pincount of the head page, but it's not. It's mapcount and
> pincount of the compound page.
OK, point taken. I might go for head_compound_mapcount()? Or as I
originally suggested, just opencoding it like we do in __page_mapcount().
next prev parent reply other threads:[~2020-08-07 15:10 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-04 21:48 [PATCH v2] mm, dump_page: do not crash with bad compound_mapcount() John Hubbard
2020-08-06 11:45 ` Vlastimil Babka
2020-08-06 13:48 ` Matthew Wilcox
2020-08-06 15:13 ` Vlastimil Babka
2020-08-06 15:39 ` Matthew Wilcox
2020-08-06 15:53 ` Vlastimil Babka
2020-08-06 17:15 ` Matthew Wilcox
2020-08-07 14:53 ` Kirill A. Shutemov
2020-08-07 14:35 ` Kirill A. Shutemov
2020-08-07 15:10 ` Matthew Wilcox [this message]
2020-08-07 16:48 ` Kirill A. Shutemov
2020-08-07 18:33 ` [PATCH] mm, dump_page: rename head_mapcount() --> head_compound_mapcount() John Hubbard
2020-08-07 22:40 ` [PATCH v2] mm, dump_page: do not crash with bad compound_mapcount() John Hubbard
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=20200807151029.GE17456@casper.infradead.org \
--to=willy@infradead.org \
--cc=akpm@linux-foundation.org \
--cc=cai@lca.pw \
--cc=jhubbard@nvidia.com \
--cc=kirill.shutemov@linux.intel.com \
--cc=kirill@shutemov.name \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=rppt@linux.ibm.com \
--cc=vbabka@suse.cz \
--cc=william.kucharski@oracle.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).