[BUG]
Syzbot reported a weird ASSERT() triggered inside prepare_to_merge().
assertion failed: root->reloc_root == reloc_root, in fs/btrfs/relocation.c:1919
------------[ cut here ]------------
kernel BUG at fs/btrfs/relocation.c:1919!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 9904 Comm: syz-executor.3 Not tainted
6.4.0-syzkaller-08881-g533925cb7604 #0
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 05/27/2023
RIP: 0010:prepare_to_merge+0xbb2/0xc40 fs/btrfs/relocation.c:1919
Code: fe e9 f5 (...)
RSP: 0018:ffffc9000325f760 EFLAGS: 00010246
RAX: 000000000000004f RBX: ffff888075644030 RCX: 1481ccc522da5800
RDX: ffffc90005c09000 RSI: 00000000000364ca RDI: 00000000000364cb
RBP: ffffc9000325f870 R08: ffffffff816f33ac R09: 1ffff9200064bea0
R10: dffffc0000000000 R11: fffff5200064bea1 R12: ffff888075644000
R13: ffff88803b166000 R14: ffff88803b166560 R15: ffff88803b166558
FS: 00007f4e305fd700(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056080679c000 CR3: 00000000193ad000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
relocate_block_group+0xa5d/0xcd0 fs/btrfs/relocation.c:3749
btrfs_relocate_block_group+0x7ab/0xd70 fs/btrfs/relocation.c:4087
btrfs_relocate_chunk+0x12c/0x3b0 fs/btrfs/volumes.c:3283
__btrfs_balance+0x1b06/0x2690 fs/btrfs/volumes.c:4018
btrfs_balance+0xbdb/0x1120 fs/btrfs/volumes.c:4402
btrfs_ioctl_balance+0x496/0x7c0 fs/btrfs/ioctl.c:3604
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl+0xf8/0x170 fs/ioctl.c:856
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f4e2f88c389
[CAUSE]
With extra debugging, the offending reloc_root is for quota tree (rootid 8).
Normally we should not use the reloc tree for quota root at all, as reloc
trees are only for subvolume trees.
But there is a race between quota enabling and relocation, this happens
after commit 85724171b3 ("btrfs: fix the btrfs_get_global_root return value").
Before that commit, for quota and free space tree, we exit immediately
if we cannot grab it from fs_info.
But now we would try to read it from disk, just as if they are fs trees,
this sets ROOT_SHAREABLE flags in such race:
Thread A | Thread B
---------------------------------+------------------------------
btrfs_quota_enable() |
| | btrfs_get_root_ref()
| | |- btrfs_get_global_root()
| | | Returned NULL
| | |- btrfs_lookup_fs_root()
| | | Returned NULL
|- btrfs_create_tree() | |
| Now quota root item is | |
| inserted | |- btrfs_read_tree_root()
| | | Got the newly inserted quota root
| | |- btrfs_init_fs_root()
| | | Set ROOT_SHAREABLE flag
[FIX]
Get back to the old behavior by returning PTR_ERR(-ENOENT) if the target
objectid is not a subvolume tree or data reloc tree.
Reported-and-tested-by: syzbot+ae97a827ae1c3336bbb4@syzkaller.appspotmail.com
Fixes: 85724171b3 ("btrfs: fix the btrfs_get_global_root return value")
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
773e722a98