[PATCH] Btrfs: Intialize btrfs_root->highest_objectid when loading tree root and subvolume roots

[Chandan Rajendra <chandan@linux.vnet.ibm.com>]

The following call trace is seen when btrfs/031 test is executed in a loop,

[  120.577208] WARNING: CPU: 3 PID: 6202 at /home/chandan/repos/linux/fs/btrfs/ioctl.c:558 create_subvol+0x3e6/0x729()
[  120.581521] BTRFS: Transaction aborted (error -2)
[  120.585410] Modules linked in:
[  120.587460] CPU: 3 PID: 6202 Comm: btrfs Not tainted 4.2.0-rc5+ #27
[  120.591232] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
[  120.596134]  ffffffff81c009d0 ffff880c846ff918 ffffffff81988f34 0000000000000001
[  120.600754]  ffff880c846ff968 ffff880c846ff958 ffffffff81050315 ffff880c846ff938
[  120.605166]  ffff880c85ae6000 ffff8809b944e000 ffff880a96c5a448 0000000000000000
[  120.609589] Call Trace:
[  120.610936]  [<ffffffff81988f34>] dump_stack+0x45/0x57
[  120.613868]  [<ffffffff81050315>] warn_slowpath_common+0x85/0xc0
[  120.616812]  [<ffffffff81050391>] warn_slowpath_fmt+0x41/0x50
[  120.619681]  [<ffffffff81985a84>] create_subvol+0x3e6/0x729
[  120.622390]  [<ffffffff8112d977>] ? zone_statistics+0x77/0x90
[  120.625111]  [<ffffffff8136577e>] btrfs_mksubvol.isra.30+0x37e/0x530
[  120.628091]  [<ffffffff8111a248>] ? __alloc_pages_nodemask+0x1b8/0x950
[  120.631091]  [<ffffffff81180f6a>] ? __mnt_want_write_file+0x1a/0x30
[  120.635156]  [<ffffffff81365a31>] btrfs_ioctl_snap_create_transid+0x101/0x180
[  120.639936]  [<ffffffff81365b02>] btrfs_ioctl_snap_create+0x52/0x70
[  120.643942]  [<ffffffff813684ae>] btrfs_ioctl+0x46e/0x2450
[  120.647204]  [<ffffffff8111f926>] ? lru_cache_add_active_or_unevictable+0x26/0x80
[  120.651647]  [<ffffffff81174dd1>] do_vfs_ioctl+0x2c1/0x4a0
[  120.655111]  [<ffffffff813be198>] ? selinux_file_ioctl+0x48/0xd0
[  120.658500]  [<ffffffff813b875e>] ? security_file_ioctl+0x3e/0x60
[  120.661680]  [<ffffffff81175024>] SyS_ioctl+0x74/0x80
[  120.664464]  [<ffffffff819932d7>] entry_SYSCALL_64_fastpath+0x12/0x6a
[  120.667824] ---[ end trace 13f2ab1e5917a256 ]---
[  120.670159] BTRFS: error (device loop0) in create_subvol:558: errno=-2 No such entry
[  120.673872] BTRFS info (device loop0): forced readonly
[  120.701265] BTRFS info (device loop0): disk space caching is enabled
[  120.704934] BTRFS error (device loop0): Remounting read-write after error is not allowed
[  120.904385] BTRFS error (device loop0): cleaner transaction attach returned -30

This occurs because,

Mount filesystem
Create subvol with ID 257
Unmount filesystem
Mount filesystem
Delete subvol with ID 257
  btrfs_drop_snapshot()
    Add root corresponding to subvol 257 into
    btrfs_transaction->dropped_roots list
Create new subvol (i.e. create_subvol())
  257 is returned as the next free objectid
  btrfs_read_fs_root_no_name()
    Finds the btrfs_root instance corresponding to the old subvol with ID 257
    in btrfs_fs_info->fs_roots_radix.
    Returns error since btrfs_root_item->refs has the value of 0.

To fix the issue the commit initializes tree root's and subvolume root's
highest_objectid when loading the roots from disk.

Signed-off-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
---
 fs/btrfs/disk-io.c   | 35 +++++++++++++++++++++++++++++++++++
 fs/btrfs/inode-map.c |  9 +--------
 fs/btrfs/inode-map.h |  1 +
 fs/btrfs/ioctl.c     |  4 ++++
 4 files changed, 41 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 807f685..3b1abe7 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1573,8 +1573,27 @@ int btrfs_init_fs_root(struct btrfs_root *root)
 	ret = get_anon_bdev(&root->anon_dev);
 	if (ret)
 		goto free_writers;
+
+	mutex_lock(&root->objectid_mutex);
+	ret = btrfs_find_highest_objectid(root,
+					&root->highest_objectid);
+	if (ret) {
+		mutex_unlock(&root->objectid_mutex);
+		goto free_root_dev;
+	}
+
+	if (unlikely(root->highest_objectid >= BTRFS_LAST_FREE_OBJECTID)) {
+		mutex_unlock(&root->objectid_mutex);
+		ret = -ENOSPC;
+		goto free_root_dev;
+	}
+
+	mutex_unlock(&root->objectid_mutex);
+
 	return 0;
 
+free_root_dev:
+	free_anon_bdev(root->anon_dev);
 free_writers:
 	btrfs_free_subvolume_writers(root->subv_writers);
 fail:
@@ -2892,6 +2911,22 @@ retry_root_backup:
 	tree_root->commit_root = btrfs_root_node(tree_root);
 	btrfs_set_root_refs(&tree_root->root_item, 1);
 
+	mutex_lock(&tree_root->objectid_mutex);
+	ret = btrfs_find_highest_objectid(tree_root,
+					&tree_root->highest_objectid);
+	if (ret) {
+		mutex_unlock(&tree_root->objectid_mutex);
+		goto recovery_tree_root;
+	}
+
+	if (unlikely(tree_root->highest_objectid >= BTRFS_LAST_FREE_OBJECTID)) {
+		mutex_unlock(&tree_root->objectid_mutex);
+		ret = -ENOSPC;
+		goto recovery_tree_root;
+	}
+
+	mutex_unlock(&tree_root->objectid_mutex);
+
 	ret = btrfs_read_roots(fs_info, tree_root);
 	if (ret)
 		goto recovery_tree_root;
diff --git a/fs/btrfs/inode-map.c b/fs/btrfs/inode-map.c
index d4a582a..9f06e8b 100644
--- a/fs/btrfs/inode-map.c
+++ b/fs/btrfs/inode-map.c
@@ -515,7 +515,7 @@ out:
 	return ret;
 }
 
-static int btrfs_find_highest_objectid(struct btrfs_root *root, u64 *objectid)
+int btrfs_find_highest_objectid(struct btrfs_root *root, u64 *objectid)
 {
 	struct btrfs_path *path;
 	int ret;
@@ -555,13 +555,6 @@ int btrfs_find_free_objectid(struct btrfs_root *root, u64 *objectid)
 	int ret;
 	mutex_lock(&root->objectid_mutex);
 
-	if (unlikely(root->highest_objectid < BTRFS_FIRST_FREE_OBJECTID)) {
-		ret = btrfs_find_highest_objectid(root,
-						  &root->highest_objectid);
-		if (ret)
-			goto out;
-	}
-
 	if (unlikely(root->highest_objectid >= BTRFS_LAST_FREE_OBJECTID)) {
 		ret = -ENOSPC;
 		goto out;
diff --git a/fs/btrfs/inode-map.h b/fs/btrfs/inode-map.h
index ddb347b..c8e864b 100644
--- a/fs/btrfs/inode-map.h
+++ b/fs/btrfs/inode-map.h
@@ -9,5 +9,6 @@ int btrfs_save_ino_cache(struct btrfs_root *root,
 			 struct btrfs_trans_handle *trans);
 
 int btrfs_find_free_objectid(struct btrfs_root *root, u64 *objectid);
+int btrfs_find_highest_objectid(struct btrfs_root *root, u64 *objectid);
 
 #endif
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 0adf542..ad7422b 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -568,6 +568,10 @@ static noinline int create_subvol(struct inode *dir,
 		goto fail;
 	}
 
+	mutex_lock(&new_root->objectid_mutex);
+	new_root->highest_objectid = new_dirid;
+	mutex_unlock(&new_root->objectid_mutex);
+
 	/*
 	 * insert the directory item
 	 */
-- 
2.1.0