Re: BUG: Bad page state (6)

[Jens Axboe <axboe@kernel.dk>]

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@syzkaller.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@syzkaller.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@googlegroups.com.
>>>
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>>> syzbot.
>>> syzbot can test patches for this bug, for details see:
>>> https://goo.gl/tpsmEJ#testing-patches
>>>
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>>
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> 
> 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@kernel.dk> (maintainer:BLOCK LAYER)
> linux-block@vger.kernel.org (open list:BLOCK LAYER)
> linux-kernel@vger.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?

-- 
Jens Axboe