Re: [PATCH] btrfs: qgroup: Fix root item corruption when multiple same source snapshiots are created with quota enabled

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2018年05月04日 00:43, David Sterba wrote:
> On Tue, Dec 19, 2017 at 03:44:54PM +0800, Qu Wenruo wrote:
>> When multiple pending snapshots referring the same source subvolume are
>> executed, enabled quota will cause root item corruption, where root
>> items are using old bytenr (no backref in extent tree).
>>
>> This can be triggered by fstests btrfs/152.
>>
>> The cause is when source subvolume is still dirty, extra commit
>> (simplied transaction commit) of qgroup_account_snapshot() can skip
>> dirty roots not recorded in current transaction, making root item of
>> source subvolume not updated.
>>
>> Fix it by forcing recording source subvolume in current transaction
>> before qgroup sub-transaction commit.
>>
>> Reported-by: Justin Maggard <jmaggard@netgear.com>
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>> ---
>>  fs/btrfs/transaction.c | 10 +++++++++-
>>  1 file changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
>> index ddae813c01dd..f645e5de5fa5 100644
>> --- a/fs/btrfs/transaction.c
>> +++ b/fs/btrfs/transaction.c
>> @@ -319,7 +319,7 @@ static int record_root_in_trans(struct btrfs_trans_handle *trans,
>>  	if ((test_bit(BTRFS_ROOT_REF_COWS, &root->state) &&
>>  	    root->last_trans < trans->transid) || force) {
>>  		WARN_ON(root == fs_info->extent_root);
>> -		WARN_ON(root->commit_root != root->node);
>> +		WARN_ON(!force && root->commit_root != root->node);
> 
> I see this warning in current misc-next, test btrfs/152. The warning
> does not appear with reference master or 'to be sent as next pull
> rquest' testing runs.

I'll try to pin down the reason,

Thanks,
Qu

> 
> All the warnings seem to be the same, so I'm pasting the first one:
> 
> [ 7910.900575] WARNING: CPU: 3 PID: 12891 at fs/btrfs/transaction.c:303record_root_in_trans+0x40/0xe0 [btrfs]
> [ 7910.973625] CPU: 3 PID: 12891 Comm: btrfs Tainted: G        W4.17.0-rc3-1.ge195904-vanilla+ #231
> [ 7910.983421] Hardware name: empty empty/S3993, BIOS PAQEX0-302/24/2008
> [ 7910.990140] RIP: 0010:record_root_in_trans+0x40/0xe0 [btrfs]
> [ 7910.995967] RSP: 0018:ffffbc7b04f1ba50 EFLAGS: 00010202
> [ 7911.001345] RAX: ffff963ef63bcd08 RBX: ffff963e069239d8 RCX:ffff963f0a89e7e8
> [ 7911.008645] RDX: 0000000000000000 RSI: ffff963f0a89e7e8 RDI:ffff963f0278b028
> [ 7911.015940] RBP: ffffbc7b04f1bb70 R08: ffff963e06923a10 R09:0000000000000001
> [ 7911.023227] R10: 0000000000200000 R11: 0000000000000000 R12:ffff963f2247c000
> [ 7911.030523] R13: ffff963f0b3e0008 R14: ffff963f0f9608c8 R15:ffff963f06561a60
> [ 7911.037834] FS:  00007fa037b1d8c0(0000) GS:ffff963f26c00000(0000)knlGS:0000000000000000
> [ 7911.047965] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 7911.053871] CR2: 00007ffeb64a8000 CR3: 0000000213d7f000 CR4:00000000000006e0
> [ 7911.061161] Call Trace:
> [ 7911.063780]  create_pending_snapshot+0x1ff/0x1130 [btrfs]
> [ 7911.069417]  ? create_pending_snapshots+0xab/0xd0 [btrfs]
> [ 7911.075000]  create_pending_snapshots+0xab/0xd0 [btrfs]
> [ 7911.080420]  btrfs_commit_transaction+0x2ac/0xa60 [btrfs]
> [ 7911.086033]  btrfs_mksubvol+0x5e8/0x650 [btrfs]
> [ 7911.090734]  ? mnt_want_write_file+0x3b/0xc0
> [ 7911.095210]  btrfs_ioctl_snap_create_transid+0x16f/0x1a0 [btrfs]
> [ 7911.101429]  btrfs_ioctl_snap_create_v2+0x102/0x150 [btrfs]
> [ 7911.107209]  btrfs_ioctl+0x39b/0x29a0 [btrfs]
> [ 7911.111730]  ? __slab_free+0xf9/0x2a0
> [ 7911.115562]  ? trace_hardirqs_on_caller+0x105/0x1c0
> [ 7911.120623]  ? do_vfs_ioctl+0x91/0x6b0
> [ 7911.124511]  do_vfs_ioctl+0x91/0x6b0
> [ 7911.128244]  ? kfree+0x259/0x310
> [ 7911.131645]  ? syscall_trace_enter+0x1ce/0x3c0
> [ 7911.136253]  ksys_ioctl+0x70/0x80
> [ 7911.139721]  ? trace_hardirqs_off_thunk+0x1a/0x1c
> [ 7911.144592]  __x64_sys_ioctl+0x16/0x20
> [ 7911.148491]  do_syscall_64+0x62/0x1c0
> [ 7911.152300]  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> [ 7911.157503] RIP: 0033:0x7fa036bba417
> [ 7911.161220] RSP: 002b:00007ffeb64ad058 EFLAGS: 00000246 ORIG_RAX:0000000000000010
> [ 7911.169028] RAX: ffffffffffffffda RBX: 00007ffeb64c2370 RCX:00007fa036bba417
> [ 7911.176316] RDX: 00007ffeb64ad0a0 RSI: 0000000050009417 RDI:0000000000000003
> [ 7911.183606] RBP: 0000000000e63020 R08: 000000000000ffff R09:00007fa036e73698
> [ 7911.190883] R10: 0000000000000000 R11: 0000000000000246 R12:0000000000e64260
> [ 7911.198171] R13: 00007ffeb64ae1d0 R14: 000000000000000e R15:00007ffeb64ad0a0
> [ 7911.224866] irq event stamp: 8428
> [ 7911.228311] hardirqs last  enabled at (8427): [<ffffffffbd3017a0>]cmpxchg_double_slab.isra.42+0x190/0x1b0
> [ 7911.238215] hardirqs last disabled at (8428): [<ffffffffbda011ac>]error_entry+0x6c/0xc0
> [ 7911.246530] softirqs last  enabled at (8418): [<ffffffffbdc00452>]__do_softirq+0x452/0x7b4
> [ 7911.255112] softirqs last disabled at (8393): [<ffffffffbd0b4043>]irq_exit+0xc3/0xf0
> [ 7911.263167] ---[ end trace 0d6ecffc816873c4 ]---
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