From: Matthew Wilcox <willy@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: syzbot <syzbot+c48f34012b06c4ac67dd@syzkaller.appspotmail.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
syzkaller-bugs@googlegroups.com,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Ralph Campbell <rcampbell@nvidia.com>,
David Hildenbrand <david@redhat.com>,
Mike Kravetz <mike.kravetz@oracle.com>
Subject: Re: kernel BUG at include/linux/swapops.h:LINE!
Date: Tue, 21 Jul 2020 03:14:49 +0100 [thread overview]
Message-ID: <20200721021449.GC15516@casper.infradead.org> (raw)
In-Reply-To: <20200721002147.GA15516@casper.infradead.org>
On Tue, Jul 21, 2020 at 01:21:47AM +0100, Matthew Wilcox wrote:
> On Mon, Jul 20, 2020 at 04:51:44PM -0700, Andrew Morton wrote:
> > On Sun, 19 Jul 2020 14:10:19 -0700 syzbot <syzbot+c48f34012b06c4ac67dd@syzkaller.appspotmail.com> wrote:
> >
> > > syzbot has found a reproducer for the following issue on:
> > >
> > > HEAD commit: 4c43049f Add linux-next specific files for 20200716
> > > git tree: linux-next
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=12c56087100000
> > > kernel config: https://syzkaller.appspot.com/x/.config?x=2c76d72659687242
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=c48f34012b06c4ac67dd
> > > compiler: gcc (GCC) 10.1.0-syz 20200507
> > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1344abeb100000
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > Reported-by: syzbot+c48f34012b06c4ac67dd@syzkaller.appspotmail.com
> >
> > Thanks.
> >
> > __handle_mm_fault
> > ->pmd_migration_entry_wait
> > ->migration_entry_to_page
> >
> > stumbled onto an unlocked page.
> >
> > I don't immediately see a cause. Perhaps Matthew's "THP prep patches",
> > perhaps something else.
>
> That's interesting. I'm currently chasing that signature too. Of course,
> almost anything can cause this.
>
> What I do have in my tree is a patch to turn that WARN_ON into a
> VM_BUG_ON_PAGE and what I see is not just an unlocked page, but one
> that's been freed.
Here's an example crash:
1404 086 (25392): drop_caches: 3
1404 page:00000000c8b7c292 refcount:0 mapcount:-128 mapping:0000000000000000 index:0x1 pfn:0xac20
1404 flags: 0x4000000000000000()
1404 raw: 4000000000000000 fffff7b501775808 fffff7b501ab7008 0000000000000000
1404 raw: 0000000000000001 0000000000000005 00000000ffffff7f 0000000000000000
1404 page dumped because: VM_BUG_ON_PAGE(!PageLocked(p))
(that's generic/086 for what it's worth, but you have to run
through a number of other tests in order to hit it; even starting at
generic/08[0123456] isn't enough to hit it, and it doesn't always hit)
A mapcount of -128 indicates PageBuddy, but I've also seen a mapcount of 0
indicating it's still on the per-cpu freelist.
next prev parent reply other threads:[~2020-07-21 2:14 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-30 17:05 kernel BUG at include/linux/swapops.h:LINE! syzbot
2020-07-19 21:10 ` syzbot
2020-07-20 23:51 ` Andrew Morton
2020-07-21 0:21 ` Matthew Wilcox
2020-07-21 2:14 ` Matthew Wilcox [this message]
2020-07-21 11:11 ` Kirill A. Shutemov
2020-07-21 15:11 ` Jens Axboe
[not found] ` <20200723073744.5268-1-hdanton@sina.com>
2020-07-24 11:13 ` Kirill A. Shutemov
2020-07-26 16:49 ` Matthew Wilcox
2020-07-27 10:31 ` Kirill A. Shutemov
2020-07-27 12:03 ` Matthew Wilcox
2020-07-29 19:21 ` Kirill A. Shutemov
2020-07-29 19:54 ` Matthew Wilcox
2020-07-29 22:11 ` Matthew Wilcox
[not found] ` <20200727125950.12048-1-hdanton@sina.com>
2020-07-27 13:44 ` Matthew Wilcox
2021-05-08 11:24 ` [syzbot] " syzbot
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