btrfs: fall back to global reservation when removing subvolumes

I recently did some ENOSPC testing that involved filling the disk
while create and removing snapshots in a loop. During the test cycle,
I ran into an ENOSPC when trying to remove a snapshot, leaving the fs
stuck in ENOSPC even after a umount/mount cycle.

This patch allow subvolume removal to fall back onto the global
block reservation in order to succeed when it would have failed
otherwise.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

3 files changed, 12 insertions, 5 deletions

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index e795bf135e80..8cc03321a368 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3175,7 +3175,7 @@ void btrfs_orphan_release_metadata(struct inode *inode);
 int btrfs_subvolume_reserve_metadata(struct btrfs_root *root,
                                      struct btrfs_block_rsv *rsv,
                                      int nitems,
-                                     u64 *qgroup_reserved);
+                                     u64 *qgroup_reserved, bool use_global_rsv);
 void btrfs_subvolume_release_metadata(struct btrfs_root *root,
                                       struct btrfs_block_rsv *rsv,
                                       u64 qgroup_reserved);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 3e7e05e6156f..7bea4d2f85dc 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4742,10 +4742,12 @@ void btrfs_orphan_release_metadata(struct inode *inode)
 int btrfs_subvolume_reserve_metadata(struct btrfs_root *root,
                                      struct btrfs_block_rsv *rsv,
                                      int items,
-                                     u64 *qgroup_reserved)
+                                     u64 *qgroup_reserved,
+                                     bool use_global_rsv)
 {
         u64 num_bytes;
         int ret;
+        struct btrfs_block_rsv *global_rsv = &root->fs_info->global_block_rsv;
 
         if (root->fs_info->quota_enabled) {
                 /* One for parent inode, two for dir entries */
@@ -4764,6 +4766,10 @@ int btrfs_subvolume_reserve_metadata(struct btrfs_root *root,
                                             BTRFS_BLOCK_GROUP_METADATA);
         ret = btrfs_block_rsv_add(root, rsv, num_bytes,
                                   BTRFS_RESERVE_FLUSH_ALL);
+
+        if (ret == -ENOSPC && use_global_rsv)
+                ret = btrfs_block_rsv_migrate(global_rsv, rsv, num_bytes);
+
         if (ret) {
                 if (*qgroup_reserved)
                         btrfs_qgroup_free(root, *qgroup_reserved);
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 238a05545ee2..841044b80658 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -396,7 +396,7 @@ static noinline int create_subvol(struct inode *dir,
          * of create_snapshot().
          */
         ret = btrfs_subvolume_reserve_metadata(root, &block_rsv,
-                                               7, &qgroup_reserved);
+                                               7, &qgroup_reserved, false);
         if (ret)
                 return ret;
 
@@ -576,7 +576,8 @@ static int create_snapshot(struct btrfs_root *root, struct inode *dir,
          */
         ret = btrfs_subvolume_reserve_metadata(BTRFS_I(dir)->root,
                                         &pending_snapshot->block_rsv, 7,
-                                        &pending_snapshot->qgroup_reserved);
+                                        &pending_snapshot->qgroup_reserved,
+                                        false);
         if (ret)
                 goto out;
 
@@ -2174,7 +2175,7 @@ static noinline int btrfs_ioctl_snap_destroy(struct file *file,
          * ref/backref.
          */
         err = btrfs_subvolume_reserve_metadata(root, &block_rsv,
-                                               5, &qgroup_reserved);
+                                               5, &qgroup_reserved, true);
         if (err)
                 goto out_up_write;