Re: [syzbot] WARNING in lookup_inline_extent_backref

[David Sterba <dsterba@suse.cz>]

On Mon, Jul 31, 2023 at 01:55:56PM +0800, Qu Wenruo wrote:
> On 2022/12/5 16:13, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    a4412fdd49dc error-injection: Add prompt for function erro..
> > git tree:       upstream
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=1469bdbd880000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=2325e409a9a893e1
> > dashboard link: https://syzkaller.appspot.com/bug?extid=d6f9ff86c1d804ba2bc6
> > compiler:       Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12d89247880000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16b1ca83880000
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/3bbe66b25958/disk-a4412fdd.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/6851483ca667/vmlinux-a4412fdd.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/2d5b23cb4616/bzImage-a4412fdd.xz
> > mounted in repro: https://storage.googleapis.com/syzbot-assets/1f178223dd56/mount_0.gz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+d6f9ff86c1d804ba2bc6@syzkaller.appspotmail.com
> >
> > ------------[ cut here ]------------
> > WARNING: CPU: 0 PID: 6559 at fs/btrfs/extent-tree.c:865 lookup_inline_extent_backref+0x8c1/0x13f0
> > Modules linked in:
> > CPU: 0 PID: 6559 Comm: syz-executor311 Not tainted 6.1.0-rc7-syzkaller-00123-ga4412fdd49dc #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
> > RIP: 0010:lookup_inline_extent_backref+0x8c1/0x13f0 fs/btrfs/extent-tree.c:865
> > Code: 98 00 00 00 0f 87 42 0b 00 00 e8 5a 9c 07 fe 4c 8b 6c 24 28 eb 3d 83 7d 28 00 4c 8b 6c 24 28 0f 84 b0 04 00 00 e8 3f 9c 07 fe <0f> 0b 41 bc fb ff ff ff e9 f3 05 00 00 e8 2d 9c 07 fe e9 ca 05 00
> > RSP: 0018:ffffc90006296e40 EFLAGS: 00010293
> > RAX: ffffffff8382fbb1 RBX: 0000000000000000 RCX: ffff88801eab1d40
> > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> > RBP: ffffc90006296ff0 R08: ffffffff8382f700 R09: ffffed100faf1008
> > R10: ffffed100faf1008 R11: 1ffff1100faf1007 R12: dffffc0000000000
> > R13: ffff888075edcd10 R14: ffffc90006296f60 R15: ffff88807d788000
> > FS:  00007fdb617d5700(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 000055912e028900 CR3: 000000001954b000 CR4: 00000000003506e0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> >   <TASK>
> >   insert_inline_extent_backref+0xcc/0x260 fs/btrfs/extent-tree.c:1152
> >   __btrfs_inc_extent_ref+0x108/0x5e0 fs/btrfs/extent-tree.c:1455
> >   btrfs_run_delayed_refs_for_head+0xf00/0x1df0 fs/btrfs/extent-tree.c:1943
> >   __btrfs_run_delayed_refs+0x25f/0x490 fs/btrfs/extent-tree.c:2008
> >   btrfs_run_delayed_refs+0x312/0x490 fs/btrfs/extent-tree.c:2139
> >   qgroup_account_snapshot+0xce/0x340 fs/btrfs/transaction.c:1538
> >   create_pending_snapshot+0xf35/0x2560 fs/btrfs/transaction.c:1800
> >   create_pending_snapshots+0x1a8/0x1e0 fs/btrfs/transaction.c:1868
> >   btrfs_commit_transaction+0x13f0/0x3760 fs/btrfs/transaction.c:2323
> >   create_snapshot+0x4aa/0x7e0 fs/btrfs/ioctl.c:833
> >   btrfs_mksubvol+0x62e/0x760 fs/btrfs/ioctl.c:983
> >   btrfs_mksnapshot+0xb5/0xf0 fs/btrfs/ioctl.c:1029
> >   __btrfs_ioctl_snap_create+0x339/0x450 fs/btrfs/ioctl.c:2184
> >   btrfs_ioctl_snap_create+0x134/0x190 fs/btrfs/ioctl.c:2211
> >   btrfs_ioctl+0x15c/0xc10
> >   vfs_ioctl fs/ioctl.c:51 [inline]
> >   __do_sys_ioctl fs/ioctl.c:870 [inline]
> >   __se_sys_ioctl+0xfb/0x170 fs/ioctl.c:856
> >   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
> >   do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
> >   entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > RIP: 0033:0x7fdb6184aa69
> > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 71 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> > RSP: 002b:00007fdb617d52f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> > RAX: ffffffffffffffda RBX: 00007fdb618d57f0 RCX: 00007fdb6184aa69
> > RDX: 00000000200000c0 RSI: 0000000050009401 RDI: 0000000000000004
> > RBP: 00007fdb618a226c R08: 00007fdb617d5700 R09: 0000000000000000
> > R10: 00007fdb617d5700 R11: 0000000000000246 R12: 8000000000000000
> > R13: 00007fdb618a1270 R14: 0000000100000000 R15: 00007fdb618d57f8
> >   </TASK>
> 
> # syz test: git://github.com/adam900710/linux.git inline_lookup_debug

There's one new repor from syzbot from 01/2024, the patch 7f72f50547b7af
("btrfs: output extra debug info if we failed to find an inline
backref") is there and adds some debugging. However, due to ordering of

WARN_ON, print_leaf, error message

the machine reboots at the end of WARN_ON, so there's no useful
debugging in the logs. I don't see a syzbot reproducer but you could ask
it to do a test with updated debugging patch or eventually send an
update to the one we have in tree.