Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752520AbdLATwu (ORCPT ); Fri, 1 Dec 2017 14:52:50 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:38924 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752283AbdLATva (ORCPT ); Fri, 1 Dec 2017 14:51:30 -0500 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, "Paul E. McKenney" , Mark Rutland , Subject: [PATCH tip/core/rcu 02/21] mn10300: READ_ONCE() now implies smp_read_barrier_depends() Date: Fri, 1 Dec 2017 11:50:57 -0800 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20171201195053.GA23494@linux.vnet.ibm.com> References: <20171201195053.GA23494@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17120119-0024-0000-0000-000002FB38C8 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008137; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000243; SDB=6.00953999; UDB=6.00482085; IPR=6.00734074; BA=6.00005726; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00018295; XFM=3.00000015; UTC=2017-12-01 19:51:22 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17120119-0025-0000-0000-00004631D6F3 Message-Id: <1512157876-24665-2-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-12-01_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=1 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1712010232 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1572 Lines: 42 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