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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 01:21:47 +0100	[thread overview]
Message-ID: <20200721002147.GA15516@casper.infradead.org> (raw)
In-Reply-To: <20200720165144.93189f7825bd28e234a42cb8@linux-foundation.org>

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.

> Is it possible to perform a bisection?

My testing (xfstests with the full THP patch set) takes about 45 minutes
to hit this bug usually.  Sometimes two hours.  I haven't tried running
it against fewer patches because I thought it was related to having THPs
smaller than PMD size in the page cache.

I don't think it is my patches because they're essentially just a rename.
But of course, I've been wrong before ...


  reply	other threads:[~2020-07-21  0:21 UTC|newest]

Thread overview: 19+ 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 [this message]
2020-07-21  2:14       ` Matthew Wilcox
2020-07-21 11:11     ` Kirill A. Shutemov
2020-07-21 15:11       ` Jens Axboe
2020-07-23  7:37       ` Hillf Danton
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
2020-07-27 12:59                 ` Hillf Danton
2020-07-27 13:44                   ` Matthew Wilcox
2020-07-27 14:46                     ` Hillf Danton
2020-07-29 19:21                 ` Kirill A. Shutemov
2020-07-29 19:54                   ` Matthew Wilcox
2020-07-29 22:11                     ` Matthew Wilcox
2021-05-08 11:24 ` [syzbot] " syzbot

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