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mn10300: READ_ONCE() now implies smp_read_barrier_depends()

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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>
This commit is contained in:
Paul E. McKenney 2017-10-09 09:17:49 -07:00
parent 4055594644
commit a4bd78ed21
1 changed files with 5 additions and 2 deletions
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7
arch/mn10300/kernel/mn10300-serial.c
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@ -550,7 +550,7 @@ try_again:
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();