From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: [PATCH 06/19] media: dvb_ringbuffer: Kill off ACCESS_ONCE() Date: Mon, 23 Oct 2017 14:07:16 -0700 Message-ID: <1508792849-3115-6-git-send-email-paulmck@linux.vnet.ibm.com> References: <20171023210408.GA2930@linux.vnet.ibm.com> Return-path: In-Reply-To: <20171023210408.GA2930@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org To: mingo@kernel.org Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, will.deacon@arm.com, mark.rutland@arm.com, snitzer@redhat.com, thor.thayer@linux.intel.com, viro@zeniv.linux.org.uk, davem@davemloft.net, shuah@kernel.org, mpe@ellerman.id.au, tj@kernel.org, torvalds@linux-foundation.org, Mauro Carvalho Chehab , Sakari Ailus List-Id: linux-arch.vger.kernel.org From: Mark Rutland For several reasons, it is desirable to use {READ,WRITE}_ONCE() in preference to ACCESS_ONCE(), and new code is expected to use one of the former. So far, there's been no reason to change most existing uses of ACCESS_ONCE(), as these aren't currently harmful. However, for some features it is necessary to instrument reads and writes separately, which is not possible with ACCESS_ONCE(). This distinction is critical to correct operation. It's possible to transform the bulk of kernel code using the Coccinelle script below. However, this doesn't handle comments, leaving references to ACCESS_ONCE() instances which have been removed. As a preparatory step, this patch converts the DVB ringbuffer code and comments to use {READ,WRITE}_ONCE() consistently. ---- virtual patch @ depends on patch @ expression E1, E2; @@ - ACCESS_ONCE(E1) = E2 + WRITE_ONCE(E1, E2) @ depends on patch @ expression E; @@ - ACCESS_ONCE(E) + READ_ONCE(E) ---- Signed-off-by: Mark Rutland Cc: Mauro Carvalho Chehab Cc: Sakari Ailus --- drivers/media/dvb-core/dvb_ringbuffer.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/media/dvb-core/dvb_ringbuffer.c b/drivers/media/dvb-core/dvb_ringbuffer.c index 2322af1b8742..53011629c9ad 100644 --- a/drivers/media/dvb-core/dvb_ringbuffer.c +++ b/drivers/media/dvb-core/dvb_ringbuffer.c @@ -66,12 +66,12 @@ ssize_t dvb_ringbuffer_free(struct dvb_ringbuffer *rbuf) { ssize_t free; - /* ACCESS_ONCE() to load read pointer on writer side + /* READ_ONCE() to load read pointer on writer side * this pairs with smp_store_release() in dvb_ringbuffer_read(), * dvb_ringbuffer_read_user(), dvb_ringbuffer_flush(), * or dvb_ringbuffer_reset() */ - free = ACCESS_ONCE(rbuf->pread) - rbuf->pwrite; + free = READ_ONCE(rbuf->pread) - rbuf->pwrite; if (free <= 0) free += rbuf->size; return free-1; @@ -143,7 +143,7 @@ ssize_t dvb_ringbuffer_read_user(struct dvb_ringbuffer *rbuf, u8 __user *buf, si todo -= split; /* smp_store_release() for read pointer update to ensure * that buf is not overwritten until read is complete, - * this pairs with ACCESS_ONCE() in dvb_ringbuffer_free() + * this pairs with READ_ONCE() in dvb_ringbuffer_free() */ smp_store_release(&rbuf->pread, 0); } @@ -168,7 +168,7 @@ void dvb_ringbuffer_read(struct dvb_ringbuffer *rbuf, u8 *buf, size_t len) todo -= split; /* smp_store_release() for read pointer update to ensure * that buf is not overwritten until read is complete, - * this pairs with ACCESS_ONCE() in dvb_ringbuffer_free() + * this pairs with READ_ONCE() in dvb_ringbuffer_free() */ smp_store_release(&rbuf->pread, 0); } -- 2.5.2 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:54068 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751619AbdJWVHm (ORCPT ); Mon, 23 Oct 2017 17:07:42 -0400 Received: from pps.filterd (m0098399.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v9NL68fl147280 for ; Mon, 23 Oct 2017 17:07:42 -0400 Received: from e18.ny.us.ibm.com (e18.ny.us.ibm.com [129.33.205.208]) by mx0a-001b2d01.pphosted.com with ESMTP id 2dsng0q0qa-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 23 Oct 2017 17:07:42 -0400 Received: from localhost by e18.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 23 Oct 2017 17:07:40 -0400 From: "Paul E. McKenney" Subject: [PATCH 06/19] media: dvb_ringbuffer: Kill off ACCESS_ONCE() Date: Mon, 23 Oct 2017 14:07:16 -0700 In-Reply-To: <20171023210408.GA2930@linux.vnet.ibm.com> References: <20171023210408.GA2930@linux.vnet.ibm.com> Message-ID: <1508792849-3115-6-git-send-email-paulmck@linux.vnet.ibm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: mingo@kernel.org Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, will.deacon@arm.com, mark.rutland@arm.com, snitzer@redhat.com, thor.thayer@linux.intel.com, viro@zeniv.linux.org.uk, davem@davemloft.net, shuah@kernel.org, mpe@ellerman.id.au, tj@kernel.org, torvalds@linux-foundation.org, Mauro Carvalho Chehab , Sakari Ailus Message-ID: <20171023210716.ezaO-zoYzCGKkCds57j2BNq7TLBAHI4axLrFl49Wl04@z> From: Mark Rutland For several reasons, it is desirable to use {READ,WRITE}_ONCE() in preference to ACCESS_ONCE(), and new code is expected to use one of the former. So far, there's been no reason to change most existing uses of ACCESS_ONCE(), as these aren't currently harmful. However, for some features it is necessary to instrument reads and writes separately, which is not possible with ACCESS_ONCE(). This distinction is critical to correct operation. It's possible to transform the bulk of kernel code using the Coccinelle script below. However, this doesn't handle comments, leaving references to ACCESS_ONCE() instances which have been removed. As a preparatory step, this patch converts the DVB ringbuffer code and comments to use {READ,WRITE}_ONCE() consistently. ---- virtual patch @ depends on patch @ expression E1, E2; @@ - ACCESS_ONCE(E1) = E2 + WRITE_ONCE(E1, E2) @ depends on patch @ expression E; @@ - ACCESS_ONCE(E) + READ_ONCE(E) ---- Signed-off-by: Mark Rutland Cc: Mauro Carvalho Chehab Cc: Sakari Ailus --- drivers/media/dvb-core/dvb_ringbuffer.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/drivers/media/dvb-core/dvb_ringbuffer.c b/drivers/media/dvb-core/dvb_ringbuffer.c index 2322af1b8742..53011629c9ad 100644 --- a/drivers/media/dvb-core/dvb_ringbuffer.c +++ b/drivers/media/dvb-core/dvb_ringbuffer.c @@ -66,12 +66,12 @@ ssize_t dvb_ringbuffer_free(struct dvb_ringbuffer *rbuf) { ssize_t free; - /* ACCESS_ONCE() to load read pointer on writer side + /* READ_ONCE() to load read pointer on writer side * this pairs with smp_store_release() in dvb_ringbuffer_read(), * dvb_ringbuffer_read_user(), dvb_ringbuffer_flush(), * or dvb_ringbuffer_reset() */ - free = ACCESS_ONCE(rbuf->pread) - rbuf->pwrite; + free = READ_ONCE(rbuf->pread) - rbuf->pwrite; if (free <= 0) free += rbuf->size; return free-1; @@ -143,7 +143,7 @@ ssize_t dvb_ringbuffer_read_user(struct dvb_ringbuffer *rbuf, u8 __user *buf, si todo -= split; /* smp_store_release() for read pointer update to ensure * that buf is not overwritten until read is complete, - * this pairs with ACCESS_ONCE() in dvb_ringbuffer_free() + * this pairs with READ_ONCE() in dvb_ringbuffer_free() */ smp_store_release(&rbuf->pread, 0); } @@ -168,7 +168,7 @@ void dvb_ringbuffer_read(struct dvb_ringbuffer *rbuf, u8 *buf, size_t len) todo -= split; /* smp_store_release() for read pointer update to ensure * that buf is not overwritten until read is complete, - * this pairs with ACCESS_ONCE() in dvb_ringbuffer_free() + * this pairs with READ_ONCE() in dvb_ringbuffer_free() */ smp_store_release(&rbuf->pread, 0); } -- 2.5.2