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Date:   Thu, 28 Feb 2019 18:53:58 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Eric Biggers <ebiggers@...nel.org>,
        syzbot <syzbot+6f5a9b79b75b66078bf0@...kaller.appspotmail.com>,
        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 6:51 PM Jens Axboe <axboe@...nel.dk> wrote:
>
> On 2/28/19 10:42 AM, Eric Biggers 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
> >>>
> >>> --
> >>> 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/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.
>
> Huh, weird. Where's the reproducer for this one?

Under the "C reproducer" link.

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