[PATCH v5 9/9] btrfs: Use sb_want_write() to protect sysfs feature change.

[Qu Wenruo]

Just like label change, use sb_want_write() to do a correct protection.

Signed-off-by: Qu Wenruo <quwen...@cn.fujitsu.com>
---
v4:
  Newly introduced.
v5:
  Change to sb_want_write().
---
 fs/btrfs/sysfs.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 3218245..64f876e 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -154,9 +154,15 @@ static ssize_t btrfs_feature_attr_store(struct kobject 
*kobj,
        btrfs_info(fs_info, "%s %s feature flag",
                   val ? "Setting" : "Clearing", fa->kobj_attr.attr.name);
 
+       ret = sb_want_write(fs_info->sb);
+       if (ret)
+               return ret;
+
        trans = btrfs_start_transaction(fs_info->fs_root, 0);
-       if (IS_ERR(trans))
-               return PTR_ERR(trans);
+       if (IS_ERR(trans)) {
+               ret = PTR_ERR(trans);
+               goto out;
+       }
 
        spin_lock(&fs_info->super_lock);
        features = get_features(fs_info, fa->feature_set);
@@ -168,10 +174,12 @@ static ssize_t btrfs_feature_attr_store(struct kobject 
*kobj,
        spin_unlock(&fs_info->super_lock);
 
        ret = btrfs_commit_transaction(trans, fs_info->fs_root);
-       if (ret)
-               return ret;
 
-       return count;
+out:
+       sb_drop_write(fs_info->sb);
+       if (!ret)
+               return count;
+       return ret;
 }
 
 static umode_t btrfs_feature_visible(struct kobject *kobj,
-- 
2.2.2

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