nilfs2: use inode_set_flags() in nilfs_set_inode_flags()

Use inode_set_flags() to atomically set i_flags instead of clearing out
the S_IMMUTABLE, S_APPEND, etc.  flags and then setting them from the
FS_IMMUTABLE_FL, FS_APPEND_FL flags to avoid a race where an immutable
file has the immutable flag cleared for a brief window of time.

This is a similar fix to commit 5f16f3225b06 ("ext4: atomically set
inode->i_flags in ext4_set_inode_flags()").

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/nilfs2/inode.c

@@ -443,19 +443,20 @@ struct inode *nilfs_new_inode(struct inode *dir, umode_t mode)
 void nilfs_set_inode_flags(struct inode *inode)
 {
 	unsigned int flags = NILFS_I(inode)->i_flags;
+	unsigned int new_fl = 0;
 
-	inode->i_flags &= ~(S_SYNC | S_APPEND | S_IMMUTABLE | S_NOATIME |
-			    S_DIRSYNC);
 	if (flags & FS_SYNC_FL)
-		inode->i_flags |= S_SYNC;
+		new_fl |= S_SYNC;
 	if (flags & FS_APPEND_FL)
-		inode->i_flags |= S_APPEND;
+		new_fl |= S_APPEND;
 	if (flags & FS_IMMUTABLE_FL)
-		inode->i_flags |= S_IMMUTABLE;
+		new_fl |= S_IMMUTABLE;
 	if (flags & FS_NOATIME_FL)
-		inode->i_flags |= S_NOATIME;
+		new_fl |= S_NOATIME;
 	if (flags & FS_DIRSYNC_FL)
-		inode->i_flags |= S_DIRSYNC;
+		new_fl |= S_DIRSYNC;
+	inode_set_flags(inode, new_fl, S_SYNC | S_APPEND | S_IMMUTABLE |
+			S_NOATIME | S_DIRSYNC);
 }
 
 int nilfs_read_inode_common(struct inode *inode,