dax: skip read lock assertion for read-only filesystems

The commit 168316d("dax: assert that i_rwsem is held
exclusive for writes") added lock assertions to ensure proper
locking in DAX operations. However, these assertions trigger
false-positive lockdep warnings since read lock is unnecessary
on read-only filesystems(e.g., erofs).

This patch skips the read lock assertion for read-only filesystems,
eliminating the spurious warnings while maintaining the integrity
checks for writable filesystems.

Fixes: 168316d ("dax: assert that i_rwsem is held exclusive for writes")
Signed-off-by: Yuezhang Mo <Yuezhang.Mo@sony.com>
Reviewed-by: Friendy Su <friendy.su@sony.com>
Reviewed-by: Daniel Palmer <daniel.palmer@sony.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: YuezhangMo

fs/dax.c

@@ -1725,7 +1725,7 @@ dax_iomap_rw(struct kiocb *iocb, struct iov_iter *iter,
 	if (iov_iter_rw(iter) == WRITE) {
 		lockdep_assert_held_write(&iomi.inode->i_rwsem);
 		iomi.flags |= IOMAP_WRITE;
-	} else {
+	} else if (!sb_rdonly(iomi.inode->i_sb)) {
 		lockdep_assert_held(&iomi.inode->i_rwsem);
 	}