btrfs: qgroup: preallocate memory before adding a relation

There's a transaction joined in the qgroup relation add/remove ioctl and
any error will lead to abort/error. We could lift the allocation from
btrfs_add_qgroup_relation() and move it outside of the transaction
context. The relation deletion does not need that.

The ownership of the structure is moved to the add relation handler.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index d28ebab..dc7300f 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3829,6 +3829,7 @@ static long btrfs_ioctl_qgroup_assign(struct file *file, void __user *arg)
        struct btrfs_fs_info *fs_info = inode_to_fs_info(inode);
        struct btrfs_root *root = BTRFS_I(inode)->root;
        struct btrfs_ioctl_qgroup_assign_args *sa;
+       struct btrfs_qgroup_list *prealloc = NULL;
        struct btrfs_trans_handle *trans;
        int ret;
        int err;
@@ -3849,14 +3850,27 @@ static long btrfs_ioctl_qgroup_assign(struct file *file, void __user *arg)
                goto drop_write;
        }
 
+       if (sa->assign) {
+               prealloc = kzalloc(sizeof(*prealloc), GFP_KERNEL);
+               if (!prealloc) {
+                       ret = -ENOMEM;
+                       goto drop_write;
+               }
+       }
+
        trans = btrfs_join_transaction(root);
        if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);
                goto out;
        }
 
+       /*
+        * Prealloc ownership is moved to the relation handler, there it's used
+        * or freed on error.
+        */
        if (sa->assign) {
-               ret = btrfs_add_qgroup_relation(trans, sa->src, sa->dst);
+               ret = btrfs_add_qgroup_relation(trans, sa->src, sa->dst, prealloc);
+               prealloc = NULL;
        } else {
                ret = btrfs_del_qgroup_relation(trans, sa->src, sa->dst);
        }
@@ -3873,6 +3887,7 @@ static long btrfs_ioctl_qgroup_assign(struct file *file, void __user *arg)
                ret = err;
 
 out:
+       kfree(prealloc);
        kfree(sa);
 drop_write:
        mnt_drop_write_file(file);

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 8b01bfd..5d57a28 100644 (file)
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -155,16 +155,6 @@ static inline u64 btrfs_qgroup_get_new_refcnt(const struct btrfs_qgroup *qg, u64
        return qg->new_refcnt - seq;
 }
 
-/*
- * glue structure to represent the relations between qgroups.
- */
-struct btrfs_qgroup_list {
-       struct list_head next_group;
-       struct list_head next_member;
-       struct btrfs_qgroup *group;
-       struct btrfs_qgroup *member;
-};
-
 static int
 qgroup_rescan_init(struct btrfs_fs_info *fs_info, u64 progress_objectid,
                   int init_flags);
@@ -1569,15 +1559,21 @@ out:
        return ret;
 }
 
-int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans, u64 src, u64 dst)
+/*
+ * Add relation between @src and @dst qgroup. The @prealloc is allocated by the
+ * callers and transferred here (either used or freed on error).
+ */
+int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans, u64 src, u64 dst,
+                             struct btrfs_qgroup_list *prealloc)
 {
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_qgroup *parent;
        struct btrfs_qgroup *member;
        struct btrfs_qgroup_list *list;
-       struct btrfs_qgroup_list *prealloc = NULL;
        int ret = 0;
 
+       ASSERT(prealloc);
+
        /* Check the level of src and dst first */
        if (btrfs_qgroup_level(src) >= btrfs_qgroup_level(dst))
                return -EINVAL;
@@ -1602,11 +1598,6 @@ int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans, u64 src, u64 dst
                }
        }
 
-       prealloc = kzalloc(sizeof(*list), GFP_NOFS);
-       if (!prealloc) {
-               ret = -ENOMEM;
-               goto out;
-       }
        ret = add_qgroup_relation_item(trans, src, dst);
        if (ret)
                goto out;

diff --git a/fs/btrfs/qgroup.h b/fs/btrfs/qgroup.h
index 95881dc..deb479d 100644 (file)
--- a/fs/btrfs/qgroup.h
+++ b/fs/btrfs/qgroup.h
@@ -278,6 +278,14 @@ struct btrfs_qgroup {
        struct kobject kobj;
 };
 
+/* Glue structure to represent the relations between qgroups. */
+struct btrfs_qgroup_list {
+       struct list_head next_group;
+       struct list_head next_member;
+       struct btrfs_qgroup *group;
+       struct btrfs_qgroup *member;
+};
+
 struct btrfs_squota_delta {
        /* The fstree root this delta counts against. */
        u64 root;
@@ -321,7 +329,8 @@ int btrfs_qgroup_rescan(struct btrfs_fs_info *fs_info);
 void btrfs_qgroup_rescan_resume(struct btrfs_fs_info *fs_info);
 int btrfs_qgroup_wait_for_completion(struct btrfs_fs_info *fs_info,
                                     bool interruptible);
-int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans, u64 src, u64 dst);
+int btrfs_add_qgroup_relation(struct btrfs_trans_handle *trans, u64 src, u64 dst,
+                             struct btrfs_qgroup_list *prealloc);
 int btrfs_del_qgroup_relation(struct btrfs_trans_handle *trans, u64 src,
                              u64 dst);
 int btrfs_create_qgroup(struct btrfs_trans_handle *trans, u64 qgroupid);