@@ -1300,6 +1300,16 @@ static struct btrfs_root *btrfs_get_root_ref(struct btrfs_fs_info *fs_info,
root = btrfs_get_global_root(fs_info, objectid);
if (root)
return root;
+
+ /*
+ * If we're called for non-subvolume trees, and above function didn't
+ * found one, do not try to read it from disk.
+ *
+ * This is mostly for fst and quota trees, which can change at runtime
+ * and should only be grabbed from fs_info.
+ */
+ if (!is_fstree(objectid) && objectid != BTRFS_DATA_RELOC_TREE_OBJECTID)
+ return ERR_PTR(-ENOENT);
again:
root = btrfs_lookup_fs_root(fs_info, objectid);
if (root) {
[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 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 85724171b302 ("btrfs: fix the btrfs_get_global_root return value"). Before that commit, for quota and free space tree, we exit immediately if we can not 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. Reviewed-by: Filipe Manana <fdmanana@suse.com> Fixes: 85724171b302 ("btrfs: fix the btrfs_get_global_root return value") Reported-and-tested-by: syzbot+ae97a827ae1c3336bbb4@syzkaller.appspotmail.com Signed-off-by: Qu Wenruo <wqu@suse.com> --- fs/btrfs/disk-io.c | 10 ++++++++++ 1 file changed, 10 insertions(+)