From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755902AbdJJAXE (ORCPT ); Mon, 9 Oct 2017 20:23:04 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:49390 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755712AbdJJAWy (ORCPT ); Mon, 9 Oct 2017 20:22:54 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, torvalds@linux-foundation.org, mark.rutland@arm.com, dhowells@redhat.com, linux-arch@vger.kernel.org, peterz@infradead.org, will.deacon@arm.com, "Paul E. McKenney" , Subject: [PATCH RFC tip/core/rcu 02/15] mn10300: READ_ONCE() now implies smp_read_barrier_depends() Date: Mon, 9 Oct 2017 17:22:36 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20171010001951.GA6476@linux.vnet.ibm.com> References: <20171010001951.GA6476@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17101000-0052-0000-0000-0000026F2FB3 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007870; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000235; SDB=6.00928858; UDB=6.00467488; IPR=6.00709129; BA=6.00005631; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00017467; XFM=3.00000015; UTC=2017-10-10 00:22:51 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17101000-0053-0000-0000-00005244CAD8 Message-Id: <1507594969-8347-2-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-10-09_07:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1707230000 definitions=main-1710100003 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Cc: David Howells Cc: Mark Rutland Cc: --- 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