btrfs: fix race when deleting quota root from the dirty cow roots list
When disabling quotas we are deleting the quota root from the list
fs_info->dirty_cowonly_roots without taking the lock that protects it,
which is struct btrfs_fs_info::trans_lock. This unsynchronized list
manipulation may cause chaos if there's another concurrent manipulation
of this list, such as when adding a root to it with
ctree.c:add_root_to_dirty_list().
This can result in all sorts of weird failures caused by a race, such as
the following crash:
[337571.278245] general protection fault, probably for non-canonical address 0xdead000000000108: 0000 [#1] PREEMPT SMP PTI
[337571.278933] CPU: 1 PID: 115447 Comm: btrfs Tainted: G W 6.4.0-rc6-btrfs-next-134+ #1
[337571.279153] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[337571.279572] RIP: 0010:commit_cowonly_roots+0x11f/0x250 [btrfs]
[337571.279928] Code: 85 38 06 00 (...)
[337571.280363] RSP: 0018:
ffff9f63446efba0 EFLAGS:
00010206
[337571.280582] RAX:
ffff942d98ec2638 RBX:
ffff9430b82b4c30 RCX:
0000000449e1c000
[337571.280798] RDX:
dead000000000100 RSI:
ffff9430021e4900 RDI:
0000000000036070
[337571.281015] RBP:
ffff942d98ec2000 R08:
ffff942d98ec2000 R09:
000000000000015b
[337571.281254] R10:
0000000000000009 R11:
0000000000000001 R12:
ffff942fe8fbf600
[337571.281476] R13:
ffff942dabe23040 R14:
ffff942dabe20800 R15:
ffff942d92cf3b48
[337571.281723] FS:
00007f478adb7340(0000) GS:
ffff94349fa40000(0000) knlGS:
0000000000000000
[337571.281950] CS: 0010 DS: 0000 ES: 0000 CR0:
0000000080050033
[337571.282184] CR2:
00007f478ab9a3d5 CR3:
000000001e02c001 CR4:
0000000000370ee0
[337571.282416] DR0:
0000000000000000 DR1:
0000000000000000 DR2:
0000000000000000
[337571.282647] DR3:
0000000000000000 DR6:
00000000fffe0ff0 DR7:
0000000000000400
[337571.282874] Call Trace:
[337571.283101] <TASK>
[337571.283327] ? __die_body+0x1b/0x60
[337571.283570] ? die_addr+0x39/0x60
[337571.283796] ? exc_general_protection+0x22e/0x430
[337571.284022] ? asm_exc_general_protection+0x22/0x30
[337571.284251] ? commit_cowonly_roots+0x11f/0x250 [btrfs]
[337571.284531] btrfs_commit_transaction+0x42e/0xf90 [btrfs]
[337571.284803] ? _raw_spin_unlock+0x15/0x30
[337571.285031] ? release_extent_buffer+0x103/0x130 [btrfs]
[337571.285305] reset_balance_state+0x152/0x1b0 [btrfs]
[337571.285578] btrfs_balance+0xa50/0x11e0 [btrfs]
[337571.285864] ? __kmem_cache_alloc_node+0x14a/0x410
[337571.286086] btrfs_ioctl+0x249a/0x3320 [btrfs]
[337571.286358] ? mod_objcg_state+0xd2/0x360
[337571.286577] ? refill_obj_stock+0xb0/0x160
[337571.286798] ? seq_release+0x25/0x30
[337571.287016] ? __rseq_handle_notify_resume+0x3ba/0x4b0
[337571.287235] ? percpu_counter_add_batch+0x2e/0xa0
[337571.287455] ? __x64_sys_ioctl+0x88/0xc0
[337571.287675] __x64_sys_ioctl+0x88/0xc0
[337571.287901] do_syscall_64+0x38/0x90
[337571.288126] entry_SYSCALL_64_after_hwframe+0x72/0xdc
[337571.288352] RIP: 0033:0x7f478aaffe9b
So fix this by locking struct btrfs_fs_info::trans_lock before deleting
the quota root from that list.
Fixes:
bed92eae26cc ("Btrfs: qgroup implementation and prototypes")
CC: stable@vger.kernel.org # 4.14+
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>