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Subject[PATCH tip/core/rcu 02/21] mn10300: READ_ONCE() now implies smp_read_barrier_depends()
Date
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>
---
arch/mn10300/kernel/mn10300-serial.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/mn10300/kernel/mn10300-serial.c b/arch/mn10300/kernel/mn10300-serial.c
index d7ef1232a82a..4994b570dfd9 100644
--- a/arch/mn10300/kernel/mn10300-serial.c
+++ b/arch/mn10300/kernel/mn10300-serial.c
@@ -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();
--
2.5.2
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