btrfs: fix warning when freeing leaf after subvolume creation failure

When creating a subvolume, at ioctl.c:create_subvol(), if we fail to
insert the root item for the new subvolume into the root tree, we can
trigger the following warning:

[78961.741046] WARNING: CPU: 0 PID: 4079814 at fs/btrfs/extent-tree.c:3357 btrfs_free_tree_block+0x2af/0x310 [btrfs]
[78961.743344] Modules linked in:
[78961.749440]  dm_snapshot dm_thin_pool (...)
[78961.773648] CPU: 0 PID: 4079814 Comm: fsstress Not tainted 5.16.0-rc4-btrfs-next-108 #1
[78961.775198] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[78961.777266] RIP: 0010:btrfs_free_tree_block+0x2af/0x310 [btrfs]
[78961.778398] Code: 17 00 48 85 (...)
[78961.781067] RSP: 0018:ffffaa4001657b28 EFLAGS: 00010202
[78961.781877] RAX: 0000000000000213 RBX: ffff897f8a796910 RCX: 0000000000000000
[78961.782780] RDX: 0000000000000000 RSI: 0000000011004000 RDI: 00000000ffffffff
[78961.783764] RBP: ffff8981f490e800 R08: 0000000000000001 R09: 0000000000000000
[78961.784740] R10: 0000000000000000 R11: 0000000000000001 R12: ffff897fc963fcc8
[78961.785665] R13: 0000000000000001 R14: ffff898063548000 R15: ffff898063548000
[78961.786620] FS:  00007f31283c6b80(0000) GS:ffff8982ace00000(0000) knlGS:0000000000000000
[78961.787717] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[78961.788598] CR2: 00007f31285c3000 CR3: 000000023fcc8003 CR4: 0000000000370ef0
[78961.789568] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[78961.790585] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[78961.791684] Call Trace:
[78961.792082]  <TASK>
[78961.792359]  create_subvol+0x5d1/0x9a0 [btrfs]
[78961.793054]  btrfs_mksubvol+0x447/0x4c0 [btrfs]
[78961.794009]  ? preempt_count_add+0x49/0xa0
[78961.794705]  __btrfs_ioctl_snap_create+0x123/0x190 [btrfs]
[78961.795712]  ? _copy_from_user+0x66/0xa0
[78961.796382]  btrfs_ioctl_snap_create_v2+0xbb/0x140 [btrfs]
[78961.797392]  btrfs_ioctl+0xd1e/0x35c0 [btrfs]
[78961.798172]  ? __slab_free+0x10a/0x360
[78961.798820]  ? rcu_read_lock_sched_held+0x12/0x60
[78961.799664]  ? lock_release+0x223/0x4a0
[78961.800321]  ? lock_acquired+0x19f/0x420
[78961.800992]  ? rcu_read_lock_sched_held+0x12/0x60
[78961.801796]  ? trace_hardirqs_on+0x1b/0xe0
[78961.802495]  ? _raw_spin_unlock_irqrestore+0x3e/0x60
[78961.803358]  ? kmem_cache_free+0x321/0x3c0
[78961.804071]  ? __x64_sys_ioctl+0x83/0xb0
[78961.804711]  __x64_sys_ioctl+0x83/0xb0
[78961.805348]  do_syscall_64+0x3b/0xc0
[78961.805969]  entry_SYSCALL_64_after_hwframe+0x44/0xae
[78961.806830] RIP: 0033:0x7f31284bc957
[78961.807517] Code: 3c 1c 48 f7 d8 (...)

This is because we are calling btrfs_free_tree_block() on an extent
buffer that is dirty. Fix that by cleaning the extent buffer, with
btrfs_clean_tree_block(), before freeing it.

This was triggered by test case generic/475 from fstests.

Fixes: 67addf2900 ("btrfs: fix metadata extent leak after failure to create subvolume")
CC: stable@vger.kernel.org # 4.4+
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ioctl.c

@@ -618,10 +618,11 @@ static noinline int create_subvol(struct user_namespace *mnt_userns,
 		 * tree block so that we don't leak space and leave the
 		 * filesystem in an inconsistent state (an extent item in the
 		 * extent tree with a backreference for a root that does not
-		 * exists). Also no need to have the tree block locked since it
-		 * is not in any tree at this point, so no other task can find
-		 * it and use it.
+		 * exists).
 		 */
+		btrfs_tree_lock(leaf);
+		btrfs_clean_tree_block(leaf);
+		btrfs_tree_unlock(leaf);
 		btrfs_free_tree_block(trans, objectid, leaf, 0, 1);
 		free_extent_buffer(leaf);
 		goto fail;