Re: kernel BUG at include/linux/page-flags.h:LINE!

[Jan Kara]

On Tue 18-09-18 07:56:03, syzbot wrote:
> Hello,
> 
> syzbot found the following crash on:
> 
> HEAD commit:    c0747ad363ff Merge tag 'linux-kselftest-4.19-rc5' of git:/..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=1483a8c9400000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=5fa12be50bca08d8
> dashboard link: https://syzkaller.appspot.com/bug?extid=5373a556df9f9fec7e90
> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> 
> Unfortunately, I don't have any reproducer for this crash yet.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+5373a556df9f9fec7e90@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ------------[ cut here ]------------
> kernel BUG at include/linux/page-flags.h:273!

Hum, looks like PageTail (i.e. the lowest bit of LRU pointer) got set for a
pagecache page we try to writeback. No idea how that's possible...

								Honza

> invalid opcode: 0000 [#1] PREEMPT SMP KASAN
> CPU: 1 PID: 9734 Comm: kworker/u4:1 Not tainted 4.19.0-rc4+ #18
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Workqueue: writeback wb_workfn (flush-7:4)
> RIP: 0010:PageWaiters include/linux/page-flags.h:273 [inline]
> RIP: 0010:wake_up_page mm/filemap.c:1069 [inline]
> RIP: 0010:end_page_writeback+0x769/0x950 mm/filemap.c:1233
> Code: ff e8 6b 25 e2 ff 48 8b 85 30 fe ff ff 4c 8d 70 ff e9 d9 fa ff ff e8
> 56 25 e2 ff 48 c7 c6 e0 24 12 88 48 89 df e8 a7 cc 13 00 <0f> 0b e8 40 25 e2
> ff 48 c7 c6 60 25 12 88 48 89 df e8 91 cc 13 00
> RSP: 0018:ffff8801b91e5288 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffffea00064dabc0 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffffffff81b08db9 RDI: ffffed003723ca42
> RBP: ffff8801b91e5460 R08: ffff880157a40400 R09: ffffed003b5e4fe8
> kobject: 'loop0' (00000000d6ad330d): kobject_uevent_env
> R10: ffffed003b5e4fe8 R11: ffff8801daf27f47 R12: 0000000000000001
> R13: 1ffff1003723ca53 R14: 1ffff1003723ca7f R15: dffffc0000000000
> FS:  0000000000000000(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f6134b6cc90 CR3: 00000001cc363000 CR4: 00000000001406e0
> kobject: 'loop0' (00000000d6ad330d): fill_kobj_path: path =
> '/devices/virtual/block/loop0'
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  page_endio+0x67c/0xb60 mm/filemap.c:1260
>  mpage_end_io+0x144/0x1e0 fs/mpage.c:54
>  bio_endio+0x5d2/0xb80 block/bio.c:1774
>  generic_make_request_checks+0x5f6/0x26c0 block/blk-core.c:2347
>  generic_make_request+0x2bd/0x15a0 block/blk-core.c:2401
>  submit_bio+0xba/0x460 block/blk-core.c:2566
>  mpage_bio_submit fs/mpage.c:66 [inline]
>  __mpage_writepage+0x1515/0x1d30 fs/mpage.c:627
>  write_cache_pages+0xd8e/0x1e50 mm/page-writeback.c:2239
>  mpage_writepages+0x14c/0x320 fs/mpage.c:730
>  fat_writepages+0x24/0x30 fs/fat/inode.c:198
>  do_writepages+0x9a/0x1a0 mm/page-writeback.c:2340
>  __writeback_single_inode+0x20a/0x1620 fs/fs-writeback.c:1323
>  writeback_sb_inodes+0x71f/0x11d0 fs/fs-writeback.c:1587
>  __writeback_inodes_wb+0x1b9/0x340 fs/fs-writeback.c:1656
>  wb_writeback+0xa73/0xfc0 fs/fs-writeback.c:1765
>  wb_check_start_all fs/fs-writeback.c:1889 [inline]
>  wb_do_writeback fs/fs-writeback.c:1915 [inline]
>  wb_workfn+0xee9/0x1790 fs/fs-writeback.c:1949
>  process_one_work+0xc90/0x1b90 kernel/workqueue.c:2153
>  worker_thread+0x17f/0x1390 kernel/workqueue.c:2296
>  kthread+0x35a/0x420 kernel/kthread.c:246
>  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:413
> Modules linked in:
> kobject: 'loop5' (0000000003a73ee3): kobject_uevent_env
> kobject: 'loop5' (0000000003a73ee3): fill_kobj_path: path =
> '/devices/virtual/block/loop5'
> ---[ end trace b1bf6d33e16c103c ]---
> RIP: 0010:PageWaiters include/linux/page-flags.h:273 [inline]
> RIP: 0010:wake_up_page mm/filemap.c:1069 [inline]
> RIP: 0010:end_page_writeback+0x769/0x950 mm/filemap.c:1233
> Code: ff e8 6b 25 e2 ff 48 8b 85 30 fe ff ff 4c 8d 70 ff e9 d9 fa ff ff e8
> 56 25 e2 ff 48 c7 c6 e0 24 12 88 48 89 df e8 a7 cc 13 00 <0f> 0b e8 40 25 e2
> ff 48 c7 c6 60 25 12 88 48 89 df e8 91 cc 13 00
> RSP: 0018:ffff8801b91e5288 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: ffffea00064dabc0 RCX: 0000000000000000
> RDX: 0000000000000000 RSI: ffffffff81b08db9 RDI: ffffed003723ca42
> kobject: 'loop2' (0000000001c28b7c): kobject_uevent_env
> RBP: ffff8801b91e5460 R08: ffff880157a40400 R09: ffffed003b5e4fe8
> kobject: 'loop2' (0000000001c28b7c): fill_kobj_path: path =
> '/devices/virtual/block/loop2'
> R10: ffffed003b5e4fe8 R11: ffff8801daf27f47 R12: 0000000000000001
> R13: 1ffff1003723ca53 R14: 1ffff1003723ca7f R15: dffffc0000000000
> FS:  0000000000000000(0000) GS:ffff8801daf00000(0000) knlGS:0000000000000000
> kobject: 'loop3' (0000000091672ed1): kobject_uevent_env
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> kobject: 'loop3' (0000000091672ed1): fill_kobj_path: path =
> '/devices/virtual/block/loop3'
> CR2: 0000001b3202d000 CR3: 00000001cad9f000 CR4: 00000000001406e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> 
> 
> ---
> This bug is generated by a bot. It may contain errors.
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> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx
> 
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-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR