From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: [PATCH 14/19] doc: filesystems: Kill off ACCESS_ONCE() Date: Mon, 23 Oct 2017 14:07:24 -0700 Message-ID: <1508792849-3115-14-git-send-email-paulmck@linux.vnet.ibm.com> References: <20171023210408.GA2930@linux.vnet.ibm.com> Return-path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:54020 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751608AbdJWVHm (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 v9NL6XIa002172 for ; Mon, 23 Oct 2017 17:07:41 -0400 Received: from e19.ny.us.ibm.com (e19.ny.us.ibm.com [129.33.205.209]) by mx0a-001b2d01.pphosted.com with ESMTP id 2dsng0q0pp-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 23 Oct 2017 17:07:41 -0400 Received: from localhost by e19.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, "Paul E. McKenney" 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 documentation, leaving references to ACCESS_ONCE() instances which have been removed. As a preparatory step, this patch converts the filesystems documentation 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: Paul E. McKenney Acked-by: Will Deacon Acked-by: Mark Rutland --- Documentation/filesystems/path-lookup.md | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/Documentation/filesystems/path-lookup.md b/Documentation/filesystems/path-lookup.md index 1b39e084a2b2..1933ef734e63 100644 --- a/Documentation/filesystems/path-lookup.md +++ b/Documentation/filesystems/path-lookup.md @@ -826,9 +826,9 @@ If the filesystem may need to revalidate dcache entries, then *is* passed the dentry but does not have access to the `inode` or the `seq` number from the `nameidata`, so it needs to be extra careful when accessing fields in the dentry. This "extra care" typically -involves using `ACCESS_ONCE()` or the newer [`READ_ONCE()`] to access -fields, and verifying the result is not NULL before using it. This -pattern can be see in `nfs_lookup_revalidate()`. +involves using [`READ_ONCE()`] to access fields, and verifying the +result is not NULL before using it. This pattern can be seen in +`nfs_lookup_revalidate()`. A pair of patterns ------------------ -- 2.5.2