From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Jann Horn <jannh@google.com>
Cc: Matthew Wilcox <willy@infradead.org>,
Linux-MM <linux-mm@kvack.org>, Zi Yan <ziy@nvidia.com>,
Peter Xu <peterx@redhat.com>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
Andrew Morton <akpm@linux-foundation.org>,
chinwen.chang@mediatek.com,
kernel list <linux-kernel@vger.kernel.org>,
syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
Vlastimil Babka <vbabka@suse.cz>,
Michel Lespinasse <walken@google.com>,
syzbot <syzbot+1f52b3a18d5633fa7f82@syzkaller.appspotmail.com>
Subject: Re: split_huge_page_to_list() races with page_mapcount() on migration entry in smaps code? [was: Re: [syzbot] kernel BUG in __page_mapcount]
Date: Mon, 7 Jun 2021 23:49:42 +0300 [thread overview]
Message-ID: <20210607204942.buratcsapp5fk627@box.shutemov.name> (raw)
In-Reply-To: <CAG48ez0M=iwJu=Q8yUQHD-+eZDg6ZF8QCF86Sb=CN1petP=Y0Q@mail.gmail.com>
On Mon, Jun 07, 2021 at 07:27:23PM +0200, Jann Horn wrote:
> 2. let smaps assume that the mapcount is 1 for all migration entries?
I believe that what we effectively do for migration entries to
non-compound pages:
for (i = 0; i < nr; i++, page++) {
int mapcount = page_mapcount(page);
unsigned long pss = PAGE_SIZE << PSS_SHIFT;
if (mapcount >= 2)
pss /= mapcount;
smaps_page_accumulate(mss, page, PAGE_SIZE, pss, dirty, locked,
mapcount < 2);
}
For non-compound pages with page_count(page) != 1 (== 1 handled
separately) we would have nr == 1 and will look into mapcount, which for
pages under migration is 0. The code above will handle mapcount == 0 as
mapcount == 1. I think it would not be a stretch to do the same for
compound pages here.
I guess we should take an additional argument to smaps_account() which would
indicate that we deal with migration entry and handle it as mapcount == 1.
Hm. Do we need the same for device-private entries?
--
Kirill A. Shutemov
next prev parent reply other threads:[~2021-06-07 20:50 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-31 0:53 [syzbot] kernel BUG in __page_mapcount syzbot
2021-06-07 17:27 ` split_huge_page_to_list() races with page_mapcount() on migration entry in smaps code? [was: Re: [syzbot] kernel BUG in __page_mapcount] Jann Horn
2021-06-07 18:03 ` Matthew Wilcox
2021-06-07 19:55 ` Jann Horn
2021-06-07 20:20 ` Matthew Wilcox
2021-06-07 20:49 ` Kirill A. Shutemov [this message]
2021-12-21 17:24 ` [syzbot] kernel BUG in __page_mapcount syzbot
2021-12-21 18:24 ` Yang Shi
2021-12-21 18:40 ` Matthew Wilcox
2021-12-21 19:07 ` Yang Shi
2021-12-22 1:42 ` Yang Shi
2022-01-05 19:05 ` Yang Shi
2022-01-11 23:14 ` Yang Shi
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