Commit a4bd78ed authored Oct 09, 2017 by Paul E. McKenney

mn10300: READ_ONCE() now implies smp_read_barrier_depends()



Given that READ_ONCE() now implies smp_read_barrier_depends(),
there is no need for the open-coded smp_read_barrier_depends() in
mn10300_serial_receive_interrupt() and mn10300_serial_poll_get_char().
This commit therefore removes them, but replaces them with comments
calling out that carrying dependencies through non-pointers is quite
dangerous.  Compilers simply know too much about integers.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: <linux-am33-list@redhat.com>

parent 40555946

arch/mn10300/kernel/mn10300-serial.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -550,7 +550,7 @@ static void mn10300_serial_receive_interrupt(struct mn10300_serial_port *port)
		return;
		}

		smp_read_barrier_depends();
		/* READ_ONCE() enforces dependency, but dangerous through integer!!! */
		ch = port->rx_buffer[ix++];
		st = port->rx_buffer[ix++];
		smp_mb();
		@@ -1728,7 +1728,10 @@ static int mn10300_serial_poll_get_char(struct uart_port *_port)
		if (CIRC_CNT(port->rx_inp, ix, MNSC_BUFFER_SIZE) == 0)
		return NO_POLL_CHAR;

		smp_read_barrier_depends();
		/*
		* READ_ONCE() enforces dependency, but dangerous
		* through integer!!!
		*/
		ch = port->rx_buffer[ix++];
		st = port->rx_buffer[ix++];
		smp_mb();