[PATCH V2] btrfs: fix warning in create_pending_snapshot

[Edward Adam Davis <eadavis@qq.com>]

[syz logs]
1.syz reported:
open("./file0", O_RDONLY)               = 4
ioctl(4, BTRFS_IOC_QUOTA_CTL, {cmd=BTRFS_QUOTA_CTL_ENABLE}) = 0
openat(AT_FDCWD, "blkio.bfq.time_recursive", O_RDWR|O_CREAT|O_NOCTTY|O_TRUNC|O_APPEND|FASYNC|0x18, 000) = 5
ioctl(5, BTRFS_IOC_QGROUP_CREATE, {create=1, qgroupid=256}) = 0
openat(AT_FDCWD, ".", O_RDONLY)         = 6
------------[ cut here ]------------
BTRFS: Transaction aborted (error -17)
WARNING: CPU: 0 PID: 5057 at fs/btrfs/transaction.c:1778 create_pending_snapshot+0x25f4/0x2b70 fs/btrfs/transaction.c:1778
Modules linked in:
CPU: 0 PID: 5057 Comm: syz-executor225 Not tainted 6.6.0-syzkaller-15365-g305230142ae0 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
RIP: 0010:create_pending_snapshot+0x25f4/0x2b70 fs/btrfs/transaction.c:1778
Code: f8 fd 48 c7 c7 00 43 ab 8b 89 de e8 76 4b be fd 0f 0b e9 30 f3 ff ff e8 7a 8d f8 fd 48 c7 c7 00 43 ab 8b 89 de e8 5c 4b be fd <0f> 0b e9 f8 f6 ff ff e8 60 8d f8 fd 48 c7 c7 00 43 ab 8b 89 de e8
RSP: 0018:ffffc90003abf580 EFLAGS: 00010246
RAX: 10fb7cf24e10ea00 RBX: 00000000ffffffef RCX: ffff888023ea9dc0
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc90003abf870 R08: ffffffff81547c82 R09: 1ffff11017305172
R10: dffffc0000000000 R11: ffffed1017305173 R12: ffff888078ae2878
R13: 00000000ffffffef R14: 0000000000000000 R15: ffff888078ae2818
FS:  000055555667d380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f6ff7bf2304 CR3: 0000000079f17000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 create_pending_snapshots+0x195/0x1d0 fs/btrfs/transaction.c:1967
 btrfs_commit_transaction+0xf1c/0x3730 fs/btrfs/transaction.c:2440
 create_snapshot+0x4a5/0x7e0 fs/btrfs/ioctl.c:845
 btrfs_mksubvol+0x5d0/0x750 fs/btrfs/ioctl.c:995
 btrfs_mksnapshot+0xb5/0xf0 fs/btrfs/ioctl.c:1041
 __btrfs_ioctl_snap_create+0x344/0x460 fs/btrfs/ioctl.c:1294
 btrfs_ioctl_snap_create+0x13c/0x190 fs/btrfs/ioctl.c:1321
 btrfs_ioctl+0xbbf/0xd40
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

2. syz repro:
r0 = open(&(0x7f0000000080)='./file0\x00', 0x0, 0x0)
ioctl$BTRFS_IOC_QUOTA_CTL(r0, 0xc0109428, &(0x7f0000000000)={0x1})
r1 = openat$cgroup_ro(0xffffffffffffff9c, &(0x7f0000000100)='blkio.bfq.time_recursive\x00', 0x275a, 0x0)
ioctl$BTRFS_IOC_QGROUP_CREATE(r1, 0x4010942a, &(0x7f0000000640)={0x1, 0x100})
r2 = openat(0xffffffffffffff9c, &(0x7f0000000500)='.\x00', 0x0, 0x0)
ioctl$BTRFS_IOC_SNAP_CREATE(r0, 0x50009401, &(0x7f0000000a80)={{r2},

[Analysis]
1. ioctl$BTRFS_IOC_QGROUP_CREATE(r1, 0x4010942a, &(0x7f0000000640)={0x1, 0x100})
After executing create qgroup, a qgroup of "qgroupid=256" will be created, 
which corresponds to the file "blkio.bfq.time_recursive".

2. ioctl$BTRFS_IOC_SNAP_CREATE(r0, 0x50009401, &(0x7f0000000a80)={{r2},
Create snap is to create a subvolume for the file0.

Therefore, the qgroup created for the file 'blkio.bfq.time_recursive' cannot 
be used for file0.

[Fix]
After added new qgroup to qgroup tree, we need to sync free_objectid use
the qgroupid, avoiding subvolume creation failure.

Reported-and-tested-by: syzbot+4d81015bc10889fd12ea@syzkaller.appspotmail.com
Fixes: 6ed05643ddb1 ("btrfs: create qgroup earlier in snapshot creation")
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 fs/btrfs/qgroup.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index edb84cc03237..9be5a836c9c0 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -218,6 +218,7 @@ static struct btrfs_qgroup *add_qgroup_rb(struct btrfs_fs_info *fs_info,
 			p = &(*p)->rb_right;
 		} else {
 			kfree(prealloc);
+			prealloc = NULL;
 			return qgroup;
 		}
 	}
@@ -1697,6 +1698,7 @@ int btrfs_create_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
 	struct btrfs_root *quota_root;
 	struct btrfs_qgroup *qgroup;
 	struct btrfs_qgroup *prealloc = NULL;
+	u64 objid;
 	int ret = 0;
 
 	if (btrfs_qgroup_mode(fs_info) == BTRFS_QGROUP_MODE_DISABLED)
@@ -1727,6 +1729,8 @@ int btrfs_create_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid)
 	spin_lock(&fs_info->qgroup_lock);
 	qgroup = add_qgroup_rb(fs_info, prealloc, qgroupid);
 	spin_unlock(&fs_info->qgroup_lock);
+	while (prealloc && !btrfs_get_free_objectid(fs_info->tree_root, 
+				&objid) && objid <= qgroupid);
 	prealloc = NULL;
 
 	ret = btrfs_sysfs_add_one_qgroup(fs_info, qgroup);
-- 
2.25.1