fs/ext4: fix comments mentioning i_mutex

inode->i_mutex has been replaced with inode->i_rwsem long ago. Fix
comments still mentioning i_mutex.

Signed-off-by: hongnanli <hongnan.li@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220121070611.21618-1-hongnan.li@linux.alibaba.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/fs/ext4/migrate.c b/fs/ext4/migrate.c
index ff8916e..7a5353a 100644
--- a/fs/ext4/migrate.c
+++ b/fs/ext4/migrate.c
@@ -485,7 +485,7 @@ int ext4_ext_migrate(struct inode *inode)
 	 * when we add extents we extent the journal
 	 */
 	/*
-	 * Even though we take i_mutex we can still cause block
+	 * Even though we take i_rwsem we can still cause block
 	 * allocation via mmap write to holes. If we have allocated
 	 * new blocks we fail migrate.  New block allocation will
 	 * clear EXT4_STATE_EXT_MIGRATE flag.  The flag is updated