From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: [PATCH 10/19] samples: mic/mpssd/mpssd.c: Kill off ACCESS_ONCE() Date: Mon, 23 Oct 2017 14:07:20 -0700 Message-ID: <1508792849-3115-10-git-send-email-paulmck@linux.vnet.ibm.com> References: <20171023210408.GA2930@linux.vnet.ibm.com> Return-path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:48350 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751525AbdJWVHl (ORCPT ); Mon, 23 Oct 2017 17:07:41 -0400 Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v9NL6A9F083459 for ; Mon, 23 Oct 2017 17:07:41 -0400 Received: from e13.ny.us.ibm.com (e13.ny.us.ibm.com [129.33.205.203]) by mx0a-001b2d01.pphosted.com with ESMTP id 2dsksdbdqd-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 23 Oct 2017 17:07:40 -0400 Received: from localhost by e13.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 In-Reply-To: <20171023210408.GA2930@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 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. The bulk of the kernel code can be transformed via Coccinelle to use {READ,WRITE}_ONCE(), though this only modifies users of ACCESS_ONCE(), and not the implementation itself. As such, it has the potential to break homebrew ACCESS_ONCE() macros seen in some user code in the kernel tree (e.g. the virtio code, as fixed in commit ea9156fb3b71d9f7). To avoid fragility if/when that transformation occurs, and to align with the preferred usage of {READ,WRITE}_ONCE(), this patch updates the MPSSD sample code to use READ_ONCE() rather than ACCESS_ONCE(). There should be no functional change as a result of this patch. Signed-off-by: Mark Rutland Cc: Shuah Khan --- samples/mic/mpssd/mpssd.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/samples/mic/mpssd/mpssd.c b/samples/mic/mpssd/mpssd.c index 49db1def1721..f42ce551bb48 100644 --- a/samples/mic/mpssd/mpssd.c +++ b/samples/mic/mpssd/mpssd.c @@ -65,7 +65,7 @@ static struct mic_info mic_list; /* to align the pointer to the (next) page boundary */ #define PAGE_ALIGN(addr) _ALIGN(addr, PAGE_SIZE) -#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) +#define READ_ONCE(x) (*(volatile typeof(x) *)&(x)) #define GSO_ENABLED 1 #define MAX_GSO_SIZE (64 * 1024) @@ -382,7 +382,7 @@ disp_iovec(struct mic_info *mic, struct mic_copy_desc *copy, static inline __u16 read_avail_idx(struct mic_vring *vr) { - return ACCESS_ONCE(vr->info->avail_idx); + return READ_ONCE(vr->info->avail_idx); } static inline void txrx_prepare(int type, bool tx, struct mic_vring *vr, @@ -523,7 +523,7 @@ spin_for_descriptors(struct mic_info *mic, struct mic_vring *vr) { __u16 avail_idx = read_avail_idx(vr); - while (avail_idx == le16toh(ACCESS_ONCE(vr->vr.avail->idx))) { + while (avail_idx == le16toh(READ_ONCE(vr->vr.avail->idx))) { #ifdef DEBUG mpsslog("%s %s waiting for desc avail %d info_avail %d\n", mic->name, __func__, -- 2.5.2