sysfs: Fix locking and factor out sysfs_sd_setattr

Cleanly separate the work that is specific to setting the
attributes of a sysfs_dirent from what is needed to update
the attributes of a vfs inode.

Additionally grab the sysfs_mutex to keep any nasties from
surprising us when updating the sysfs_dirent.
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Eric W. Biederman <ebiederm@aristanetworks.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/sysfs/inode.c

@@ -65,30 +65,14 @@ static struct sysfs_inode_attrs *sysfs_init_inode_attrs(struct sysfs_dirent *sd)
 	return attrs;
 }
 
-int sysfs_setattr(struct dentry * dentry, struct iattr * iattr)
+int sysfs_sd_setattr(struct sysfs_dirent *sd, struct iattr * iattr)
 {
-	struct inode * inode = dentry->d_inode;
-	struct sysfs_dirent * sd = dentry->d_fsdata;
 	struct sysfs_inode_attrs *sd_attrs;
 	struct iattr *iattrs;
 	unsigned int ia_valid = iattr->ia_valid;
-	int error;
-
-	if (!sd)
-		return -EINVAL;
 
 	sd_attrs = sd->s_iattr;
 
-	error = inode_change_ok(inode, iattr);
-	if (error)
-		return error;
-
-	iattr->ia_valid &= ~ATTR_SIZE; /* ignore size changes */
-
-	error = inode_setattr(inode, iattr);
-	if (error)
-		return error;
-
 	if (!sd_attrs) {
 		/* setting attributes for the first time, allocate now */
 		sd_attrs = sysfs_init_inode_attrs(sd);
@@ -111,12 +95,39 @@ int sysfs_setattr(struct dentry * dentry, struct iattr * iattr)
 			iattrs->ia_ctime = iattr->ia_ctime;
 		if (ia_valid & ATTR_MODE) {
 			umode_t mode = iattr->ia_mode;
-
-			if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
-				mode &= ~S_ISGID;
 			iattrs->ia_mode = sd->s_mode = mode;
 		}
 	}
+	return 0;
+}
+
+int sysfs_setattr(struct dentry *dentry, struct iattr *iattr)
+{
+	struct inode *inode = dentry->d_inode;
+	struct sysfs_dirent *sd = dentry->d_fsdata;
+	int error;
+
+	if (!sd)
+		return -EINVAL;
+
+	error = inode_change_ok(inode, iattr);
+	if (error)
+		return error;
+
+	iattr->ia_valid &= ~ATTR_SIZE; /* ignore size changes */
+	if (iattr->ia_valid & ATTR_MODE) {
+		if (!in_group_p(inode->i_gid) && !capable(CAP_FSETID))
+			iattr->ia_mode &= ~S_ISGID;
+	}
+
+	error = inode_setattr(inode, iattr);
+	if (error)
+		return error;
+
+	mutex_lock(&sysfs_mutex);
+	error = sysfs_sd_setattr(sd, iattr);
+	mutex_unlock(&sysfs_mutex);
+
 	return error;
 }
 

fs/sysfs/sysfs.h

@@ -155,6 +155,7 @@ static inline void __sysfs_put(struct sysfs_dirent *sd)
  */
 struct inode *sysfs_get_inode(struct sysfs_dirent *sd);
 void sysfs_delete_inode(struct inode *inode);
+int sysfs_sd_setattr(struct sysfs_dirent *sd, struct iattr *iattr);
 int sysfs_setattr(struct dentry *dentry, struct iattr *iattr);
 int sysfs_setxattr(struct dentry *dentry, const char *name, const void *value,
 		size_t size, int flags);