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Date:   Thu, 28 Feb 2019 19:04:01 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     syzbot <syzbot+6f5a9b79b75b66078bf0@...kaller.appspotmail.com>,
        Jens Axboe <axboe@...nel.dk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        arunks@...eaurora.org, Dan Williams <dan.j.williams@...el.com>,
        Lance Roy <ldr709@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, Michal Hocko <mhocko@...e.com>,
        nborisov@...e.com, Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Matthew Wilcox <willy@...radead.org>, yuehaibing@...wei.com
Subject: Re: BUG: Bad page state (6)

On Thu, Feb 28, 2019 at 6:42 PM Eric Biggers <ebiggers@...nel.org> wrote:
>
> On Thu, Feb 28, 2019 at 11:36:21AM +0100, 'Dmitry Vyukov' via syzkaller-bugs wrote:
> > On Thu, Feb 28, 2019 at 11:32 AM syzbot
> > <syzbot+6f5a9b79b75b66078bf0@...kaller.appspotmail.com> wrote:
> > >
> > > Hello,
> > >
> > > syzbot found the following crash on:
> > >
> > > HEAD commit:    42fd8df9d1d9 Add linux-next specific files for 20190228
> > > git tree:       linux-next
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=179ba9e0c00000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=c0f38652d28b522f
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=6f5a9b79b75b66078bf0
> > > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12ed6bd0c00000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10690c8ac00000
> > >
> > > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > > Reported-by: syzbot+6f5a9b79b75b66078bf0@...kaller.appspotmail.com
> >
> > +Jens, Eric,
> >
> > Looks similar to:
> > https://groups.google.com/forum/#!msg/syzkaller-bugs/E3v3XQweVBw/6BPrkIYJIgAJ
> > Perhaps the fixing commit is not in the build yet?
> >
> >
> > > BUG: Bad page state in process syz-executor193  pfn:9225a
> > > page:ffffea0002489680 count:0 mapcount:0 mapping:ffff88808652fd80 index:0x81
> > > shmem_aops
> > > name:"memfd:cgroup2"
> > > flags: 0x1fffc000008000e(referenced|uptodate|dirty|swapbacked)
> > > raw: 01fffc000008000e ffff88809277fac0 ffff88809277fac0 ffff88808652fd80
> > > raw: 0000000000000081 0000000000000000 00000000ffffffff 0000000000000000
> > > page dumped because: non-NULL mapping
> > > Modules linked in:
> > > CPU: 0 PID: 7659 Comm: syz-executor193 Not tainted 5.0.0-rc8-next-20190228
> > > #45
> > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> > > Google 01/01/2011
> > > Call Trace:
> > >   __dump_stack lib/dump_stack.c:77 [inline]
> > >   dump_stack+0x172/0x1f0 lib/dump_stack.c:113
> > >   bad_page.cold+0xda/0xff mm/page_alloc.c:586
> > >   free_pages_check_bad+0x142/0x1a0 mm/page_alloc.c:1013
> > >   free_pages_check mm/page_alloc.c:1022 [inline]
> > >   free_pages_prepare mm/page_alloc.c:1112 [inline]
> > >   free_pcp_prepare mm/page_alloc.c:1137 [inline]
> > >   free_unref_page_prepare mm/page_alloc.c:3001 [inline]
> > >   free_unref_page_list+0x31d/0xc40 mm/page_alloc.c:3070
> > >   release_pages+0x60d/0x1940 mm/swap.c:794
> > >   pagevec_lru_move_fn+0x218/0x2a0 mm/swap.c:213
> > >   activate_page_drain mm/swap.c:297 [inline]
> > >   lru_add_drain_cpu+0x3b1/0x520 mm/swap.c:596
> > >   lru_add_drain+0x20/0x60 mm/swap.c:647
> > >   exit_mmap+0x290/0x530 mm/mmap.c:3134
> > >   __mmput kernel/fork.c:1047 [inline]
> > >   mmput+0x15f/0x4c0 kernel/fork.c:1068
> > >   exit_mm kernel/exit.c:546 [inline]
> > >   do_exit+0x816/0x2fa0 kernel/exit.c:863
> > >   do_group_exit+0x135/0x370 kernel/exit.c:980
> > >   __do_sys_exit_group kernel/exit.c:991 [inline]
> > >   __se_sys_exit_group kernel/exit.c:989 [inline]
> > >   __x64_sys_exit_group+0x44/0x50 kernel/exit.c:989
> > >   do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
> > >   entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > > RIP: 0033:0x442a58
> > > Code: 00 00 be 3c 00 00 00 eb 19 66 0f 1f 84 00 00 00 00 00 48 89 d7 89 f0
> > > 0f 05 48 3d 00 f0 ff ff 77 21 f4 48 89 d7 44 89 c0 0f 05 <48> 3d 00 f0 ff
> > > ff 76 e0 f7 d8 64 41 89 01 eb d8 0f 1f 84 00 00 00
> > > RSP: 002b:00007ffe99e2faf8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
> > > RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000442a58
> > > RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
> > > RBP: 00000000004c2468 R08: 00000000000000e7 R09: ffffffffffffffd0
> > > R10: 0000000002000005 R11: 0000000000000246 R12: 0000000000000001
> > > R13: 00000000006d4180 R14: 0000000000000000 R15: 0000000000000000
> > >
> > >
> > > ---
> > > This bug is generated by a bot. It may contain errors.
> > > See https://goo.gl/tpsmEJ for more information about syzbot.
> > > syzbot engineers can be reached at syzkaller@...glegroups.com.
> > >
> > > syzbot will keep track of this bug report. See:
> > > https://goo.gl/tpsmEJ#bug-status-tracking for how to communicate with
> > > syzbot.
> > > syzbot can test patches for this bug, for details see:
> > > https://goo.gl/tpsmEJ#testing-patches
> > >
> > > --
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> > > To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@...glegroups.com.
> > > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/00000000000024b3aa0582f1cde7%40google.com.
> > > For more options, visit https://groups.google.com/d/optout.
> >
> > --
> > You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group.
> > To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@...glegroups.com.
> > To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/CACT4Y%2BbyrcaasUaEJj%3DhcemEEBBkon%3DVC24gPwGXHzfeRP0E3w%40mail.gmail.com.
> > For more options, visit https://groups.google.com/d/optout.
>
> It bisects down to the same patch ("block: implement bio helper to add iter bvec
> pages to bio") so apparently it's just still broken despite Jens' fix.
>
> BTW, as this is trivially bisectable with the reproducer, I still don't see why
> syzbot can't do the bisection itself and use get_maintainer.pl on the broken
> patch to actually send the report to the right person:
>
> $ ./scripts/get_maintainer.pl 0001-block-implement-bio-helper-to-add-iter-bvec-pages-to.patch
> Jens Axboe <axboe@...nel.dk> (maintainer:BLOCK LAYER)
> linux-block@...r.kernel.org (open list:BLOCK LAYER)
> linux-kernel@...r.kernel.org (open list)
>
> Spamming unrelated lists and maintainers not only prevents the bug from being
> fixed, but it also reduces the average usefulness of syzbot reports which
> teaches people to ignore them.


It can. It's just lots of work to code generic logic that can reliably
handle all possible cases in fully automated fashion, build production
pipeline that will schedule and execute all of this, built in
necessary introspection, design persistent data formats, etc.

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