btrfs: fix block_group_tree dirty_list corruption

In the Linux kernel, the following vulnerability has been resolved:

btrfs: fix block_group_tree dirty_list corruption

When the incompat flag EXTENT_TREE_V2 is set, we unconditionally add the
block group tree to the switch_commits list before calling
switch_commit_roots, as we do for the tree root and the chunk root.
However, the block group tree uses normal root dirty tracking and in any
transaction that does an allocation and dirties a block group, the block
group root will already be linked to a list by the dirty_list field and
this use of list_add_tail() is invalid and corrupts the prev/next
members of block_group_root->dirty_list.

This is apparent on a subsequent list_del on the prev if we enable
CONFIG_DEBUG_LIST:

[32.1571] ------------[ cut here ]------------
[32.1572] list_del corruption. next->prev should beffff958890202538, but was ffff9588992bd538. (next=ffff958890201538)
[32.1575] WARNING: lib/list_debug.c:65 at 0x0, CPU#3: sync/607
[32.1583] CPU: 3 UID: 0 PID: 607 Comm: sync Not tainted 6.18.0 #24PREEMPT(none)
[32.1585] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS1.17.0-4.fc41 04/01/2014
[32.1587] RIP: 0010:__list_del_entry_valid_or_report+0x108/0x120
[32.1593] RSP: 0018:ffffaa288287fdd0 EFLAGS: 00010202
[32.1594] RAX: 0000000000000001 RBX: ffff95889326e800 RCX:ffff958890201538
[32.1596] RDX: ffff9588992bd538 RSI: ffff958890202538 RDI:ffffffff82a41e00
[32.1597] RBP: ffff958890202538 R08: ffffffff828fc1e8 R09:00000000ffffefff
[32.1599] R10: ffffffff8288c200 R11: ffffffff828e4200 R12:ffff958890201538
[32.1601] R13: ffff95889326e958 R14: ffff958895c24000 R15:ffff958890202538
[32.1603] FS: 00007f0c28eb5740(0000) GS:ffff958af2bd2000(0000)knlGS:0000000000000000
[32.1605] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[32.1607] CR2: 00007f0c28e8a3cc CR3: 0000000109942005 CR4:0000000000370ef0
[32.1609] Call Trace:
[32.1610] <TASK>
[32.1611] switch_commit_roots+0x82/0x1d0 [btrfs]
[32.1615] btrfs_commit_transaction+0x968/0x1550 [btrfs]
[32.1618] ? btrfs_attach_transaction_barrier+0x23/0x60 [btrfs]
[32.1621] __iterate_supers+0xe8/0x190
[32.1622] ? __pfx_sync_fs_one_sb+0x10/0x10
[32.1623] ksys_sync+0x63/0xb0
[32.1624] __do_sys_sync+0xe/0x20
[32.1625] do_syscall_64+0x73/0x450
[32.1626] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[32.1627] RIP: 0033:0x7f0c28d05d2b
[32.1632] RSP: 002b:00007ffc9d988048 EFLAGS: 00000246 ORIG_RAX:00000000000000a2
[32.1634] RAX: ffffffffffffffda RBX: 00007ffc9d988228 RCX:00007f0c28d05d2b
[32.1636] RDX: 00007f0c28e02301 RSI: 00007ffc9d989b21 RDI:00007f0c28dba90d
[32.1637] RBP: 0000000000000001 R08: 0000000000000001 R09:0000000000000000
[32.1639] R10: 0000000000000000 R11: 0000000000000246 R12:000055b96572cb80
[32.1641] R13: 000055b96572b19f R14: 00007f0c28dfa434 R15:000055b96572b034
[32.1643] </TASK>
[32.1644] irq event stamp: 0
[32.1644] hardirqs last enabled at (0): [<0000000000000000>] 0x0
[32.1646] hardirqs last disabled at (0): [<ffffffff81298817>]copy_process+0xb37/0x2260
[32.1648] softirqs last enabled at (0): [<ffffffff81298817>]copy_process+0xb37/0x2260
[32.1650] softirqs last disabled at (0): [<0000000000000000>] 0x0
[32.1652] ---[ end trace 0000000000000000 ]---

Furthermore, this list corruption eventually (when we happen to add a
new block group) results in getting the switch_commits and
dirty_cowonly_roots lists mixed up and attempting to call update_root
on the tree root which can't be found in the tree root, resulting in a
transaction abort:

[87.8269] BTRFS critical (device nvme1n1): unable to find root key (1 0 0) in tree 1
[87.8272] ------------[ cut here ]------------
[87.8274] BTRFS: Transaction aborted (error -117)
[87.8275] WARNING: fs/btrfs/root-tree.c:153 at 0x0, CPU#4: sync/703
[87.8285] CPU: 4 UID: 0 PID: 703 Comm: sync Not tainted 6.18.0 #25 PREEMPT(none)
[87.8287] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.17.0-4.fc41 0
---truncated---