tty: tty_io: Switch to vmalloc() fallback in case of TTY_NO_WRITE_SPLIT

When TTY_NO_WRITE_SPLIT is set and 64 KiB chunks are used, allow
vmalloc() fallback. Supply __GFP_RETRY_MAYFAIL to make kmalloc()
preferable over vmalloc() since we may want a better performance.

Note, both current users copy data to another buffer anyway, so
the type of our allocation doesn't affect their expectations.

Signed-off-by: Andy Shevchenko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/tty_io.c

···
 {
 	tty_ldisc_deinit(tty);
 	put_device(tty->dev);
-	kfree(tty->write_buf);
+	kvfree(tty->write_buf);
 	tty->magic = 0xDEADDEAD;
 	kfree(tty);
 }
···
 	 * layer has problems with bigger chunks. It will
 	 * claim to be able to handle more characters than
 	 * it actually does.
-	 *
-	 * FIXME: This can probably go away now except that 64K chunks
-	 * are too likely to fail unless switched to vmalloc...
 	 */
 	chunk = 2048;
 	if (test_bit(TTY_NO_WRITE_SPLIT, &tty->flags))
···
 		if (chunk < 1024)
 			chunk = 1024;
 
-		buf_chunk = kmalloc(chunk, GFP_KERNEL);
+		buf_chunk = kvmalloc(chunk, GFP_KERNEL | __GFP_RETRY_MAYFAIL);
 		if (!buf_chunk) {
 			ret = -ENOMEM;
 			goto out;
 		}
-		kfree(tty->write_buf);
+		kvfree(tty->write_buf);
 		tty->write_cnt = chunk;
 		tty->write_buf = buf_chunk;
 	}

drivers/usb/class/cdc-acm.c

···
 	if (retval)
 		goto error_get_interface;
 
-	/*
-	 * FIXME: Why do we need this? Allocating 64K of physically contiguous
-	 * memory is really nasty...
-	 */
 	set_bit(TTY_NO_WRITE_SPLIT, &tty->flags);
 	acm->control->needs_remote_wakeup = 1;