Re: BUG: Bad page state (6)

[Jens Axboe]

On 2/28/19 10:53 AM, Dmitry Vyukov wrote:
> On Thu, Feb 28, 2019 at 6:51 PM Jens Axboe <axboe@xxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
>>>>
>>>> +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@xxxxxxxxxxxxxxxxx
>>>>>
>>>>> 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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>>>>
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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@xxxxxxxxx> (maintainer:BLOCK LAYER)
>>> linux-block@xxxxxxxxxxxxxxx (open list:BLOCK LAYER)
>>> linux-kernel@xxxxxxxxxxxxxxx (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.

This doesn't reproduce for me, but I think that's because there was a
bug in the mp_bvec_for_each_page() helper. I merged a fix for it this
morning, should be fine after that.

-- 
Jens Axboe