Re: WARNING in btrfs_alloc_chunk

[David Sterba]

On Mon, Sep 21, 2020 at 03:02:22AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    325d0eab Merge branch 'akpm' (patches from Andrew)
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=142c89ab900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=8d39f8ae68f9dcd5
> dashboard link: https://syzkaller.appspot.com/bug?extid=f54bbed7adc7c7729120
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+f54bbed7adc7c7729120@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ------------[ cut here ]------------
> gather_device_info: found more than 0 devices
> WARNING: CPU: 1 PID: 26278 at fs/btrfs/volumes.c:4967 gather_device_info fs/btrfs/volumes.c:4967 [inline]
> WARNING: CPU: 1 PID: 26278 at fs/btrfs/volumes.c:4967 btrfs_alloc_chunk+0x1a43/0x2000 fs/btrfs/volumes.c:5194
> Kernel panic - not syncing: panic_on_warn set ...
> CPU: 1 PID: 26278 Comm: syz-executor.2 Not tainted 5.9.0-rc5-syzkaller #0
> 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+0x198/0x1fd lib/dump_stack.c:118
>  panic+0x382/0x7fb kernel/panic.c:231
>  __warn.cold+0x20/0x4b kernel/panic.c:600
>  report_bug+0x1bd/0x210 lib/bug.c:198
>  handle_bug+0x38/0x90 arch/x86/kernel/traps.c:234
>  exc_invalid_op+0x14/0x40 arch/x86/kernel/traps.c:254
>  asm_exc_invalid_op+0x12/0x20 arch/x86/include/asm/idtentry.h:536
> RIP: 0010:gather_device_info fs/btrfs/volumes.c:4967 [inline]
> RIP: 0010:btrfs_alloc_chunk+0x1a43/0x2000 fs/btrfs/volumes.c:5194
> Code: ff ff 44 8b 7c 24 78 4c 89 0c 24 e8 17 06 67 fe 4c 8b 0c 24 48 c7 c6 c0 79 a6 88 48 c7 c7 40 67 a6 88 4c 89 ca e8 ff 41 37 fe <0f> 0b 4c 8b 0c 24 e9 f8 f0 ff ff 44 8b 7c 24 78 e8 e8 05 67 fe 31
> RSP: 0018:ffffc900049072a8 EFLAGS: 00010286
> RAX: 0000000000000000 RBX: ffff88809cbee000 RCX: 0000000000000000
> RDX: ffff8880645462c0 RSI: ffffffff815f5a85 RDI: fffff52000920e47
> RBP: dffffc0000000000 R08: 0000000000000001 R09: ffff8880ae7318e7
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: 0000000002800000 R14: 0000000000010000 R15: 0000000000000001
>  btrfs_chunk_alloc+0x3fe/0xaa0 fs/btrfs/block-group.c:3136
>  find_free_extent_update_loop fs/btrfs/extent-tree.c:3796 [inline]
>  find_free_extent+0x2090/0x2e60 fs/btrfs/extent-tree.c:4127
>  btrfs_reserve_extent+0x166/0x460 fs/btrfs/extent-tree.c:4206
>  btrfs_alloc_tree_block+0x203/0xee0 fs/btrfs/extent-tree.c:4603
>  alloc_tree_block_no_bg_flush+0x1b6/0x250 fs/btrfs/ctree.c:987
>  __btrfs_cow_block+0x3e0/0x10c0 fs/btrfs/ctree.c:1042
>  btrfs_cow_block+0x2c1/0x8a0 fs/btrfs/ctree.c:1487
>  commit_cowonly_roots+0x129/0xc70 fs/btrfs/transaction.c:1184
>  btrfs_commit_transaction+0xde0/0x2830 fs/btrfs/transaction.c:2272
>  btrfs_commit_super+0xc1/0x100 fs/btrfs/disk-io.c:4021
>  close_ctree+0x2cd/0x6cb fs/btrfs/disk-io.c:4084
>  generic_shutdown_super+0x144/0x370 fs/super.c:464
>  kill_anon_super+0x36/0x60 fs/super.c:1108
>  btrfs_kill_super+0x38/0x50 fs/btrfs/super.c:2265
>  deactivate_locked_super+0x94/0x160 fs/super.c:335
>  deactivate_super+0xad/0xd0 fs/super.c:366
>  cleanup_mnt+0x3a3/0x530 fs/namespace.c:1118
>  task_work_run+0xdd/0x190 kernel/task_work.c:141
>  tracehook_notify_resume include/linux/tracehook.h:188 [inline]
>  exit_to_user_mode_loop kernel/entry/common.c:163 [inline]
>  exit_to_user_mode_prepare+0x1e1/0x200 kernel/entry/common.c:190
>  syscall_exit_to_user_mode+0x7e/0x2e0 kernel/entry/common.c:265
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x460027
> Code: 64 89 04 25 d0 02 00 00 58 5f ff d0 48 89 c7 e8 2f be ff ff 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 b8 a6 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 fd 89 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007ffd0b14c408 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000460027
> RDX: 0000000000403188 RSI: 0000000000000002 RDI: 00007ffd0b14c4b0
> RBP: 00000000000000ce R08: 0000000000000000 R09: 000000000000000a
> R10: 0000000000000005 R11: 0000000000000246 R12: 00007ffd0b14d540
> R13: 0000000002358a60 R14: 0000000000000000 R15: 00007ffd0b14d540
> Kernel Offset: disabled
> Rebooting in 86400 seconds..

#syz test: git://github.com/kdave/btrfs-devel.git misc-5.9