iomap: allocate s_dio_done_wq for async reads as well

Since commit 222f2c7 ("iomap: always run error completions in user
context"), read error completions are deferred to s_dio_done_wq.  This
means the workqueue also needs to be allocated for async reads.

Fixes: 222f2c7 ("iomap: always run error completions in user context")
Reported-by: syzbot+a2b9a4ed0d61b1efb3f5@syzkaller.appspotmail.com
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20251124140013.902853-1-hch@lst.de
Tested-by: syzbot+a2b9a4ed0d61b1efb3f5@syzkaller.appspotmail.com
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Christoph Hellwig

fs/iomap/direct-io.c

@@ -734,12 +734,12 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 			}
 			goto out_free_dio;
 		}
+	}
 
-		if (!wait_for_completion && !inode->i_sb->s_dio_done_wq) {
-			ret = sb_init_dio_done_wq(inode->i_sb);
-			if (ret < 0)
-				goto out_free_dio;
-		}
+	if (!wait_for_completion && !inode->i_sb->s_dio_done_wq) {
+		ret = sb_init_dio_done_wq(inode->i_sb);
+		if (ret < 0)
+			goto out_free_dio;
 	}
 
 	inode_dio_begin(inode);