From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755268AbdJISas (ORCPT ); Mon, 9 Oct 2017 14:30:48 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:33766 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755110AbdJISaq (ORCPT ); Mon, 9 Oct 2017 14:30:46 -0400 From: Mark Rutland To: linux-kernel@vger.kernel.org Cc: Mark Rutland , Al Viro , Andrew Morton Subject: [PATCH 04/13] fs: dcache: kill off ACCESS_ONCE() Date: Mon, 9 Oct 2017 19:28:41 +0100 Message-Id: <1507573730-8083-5-git-send-email-mark.rutland@arm.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1507573730-8083-1-git-send-email-mark.rutland@arm.com> References: <1507573730-8083-1-git-send-email-mark.rutland@arm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 dcache 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: Al Viro Cc: Andrew Morton --- fs/dcache.c | 18 +++++++++--------- include/linux/dcache.h | 4 ++-- 2 files changed, 11 insertions(+), 11 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index f901413..f283cd3 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -630,7 +630,7 @@ static inline struct dentry *lock_parent(struct dentry *dentry) rcu_read_lock(); spin_unlock(&dentry->d_lock); again: - parent = ACCESS_ONCE(dentry->d_parent); + parent = READ_ONCE(dentry->d_parent); spin_lock(&parent->d_lock); /* * We can't blindly lock dentry until we are sure @@ -721,7 +721,7 @@ static inline bool fast_dput(struct dentry *dentry) * around with a zero refcount. */ smp_rmb(); - d_flags = ACCESS_ONCE(dentry->d_flags); + d_flags = READ_ONCE(dentry->d_flags); d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_DISCONNECTED; /* Nothing to do? Dropping the reference was all we needed? */ @@ -850,11 +850,11 @@ struct dentry *dget_parent(struct dentry *dentry) * locking. */ rcu_read_lock(); - ret = ACCESS_ONCE(dentry->d_parent); + ret = READ_ONCE(dentry->d_parent); gotref = lockref_get_not_zero(&ret->d_lockref); rcu_read_unlock(); if (likely(gotref)) { - if (likely(ret == ACCESS_ONCE(dentry->d_parent))) + if (likely(ret == READ_ONCE(dentry->d_parent))) return ret; dput(ret); } @@ -3040,7 +3040,7 @@ static int prepend(char **buffer, int *buflen, const char *str, int namelen) * @buflen: allocated length of the buffer * @name: name string and length qstr structure * - * With RCU path tracing, it may race with d_move(). Use ACCESS_ONCE() to + * With RCU path tracing, it may race with d_move(). Use READ_ONCE() to * make sure that either the old or the new name pointer and length are * fetched. However, there may be mismatch between length and pointer. * The length cannot be trusted, we need to copy it byte-by-byte until @@ -3054,8 +3054,8 @@ static int prepend(char **buffer, int *buflen, const char *str, int namelen) */ static int prepend_name(char **buffer, int *buflen, const struct qstr *name) { - const char *dname = ACCESS_ONCE(name->name); - u32 dlen = ACCESS_ONCE(name->len); + const char *dname = READ_ONCE(name->name); + u32 dlen = READ_ONCE(name->len); char *p; smp_read_barrier_depends(); @@ -3120,7 +3120,7 @@ static int prepend_path(const struct path *path, struct dentry * parent; if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) { - struct mount *parent = ACCESS_ONCE(mnt->mnt_parent); + struct mount *parent = READ_ONCE(mnt->mnt_parent); /* Escaped? */ if (dentry != vfsmnt->mnt_root) { bptr = *buffer; @@ -3130,7 +3130,7 @@ static int prepend_path(const struct path *path, } /* Global root? */ if (mnt != parent) { - dentry = ACCESS_ONCE(mnt->mnt_mountpoint); + dentry = READ_ONCE(mnt->mnt_mountpoint); mnt = parent; vfsmnt = &mnt->mnt; continue; diff --git a/include/linux/dcache.h b/include/linux/dcache.h index ed1a7cf..1d8f581 100644 --- a/include/linux/dcache.h +++ b/include/linux/dcache.h @@ -519,7 +519,7 @@ static inline struct inode *d_inode(const struct dentry *dentry) } /** - * d_inode_rcu - Get the actual inode of this dentry with ACCESS_ONCE() + * d_inode_rcu - Get the actual inode of this dentry with READ_ONCE() * @dentry: The dentry to query * * This is the helper normal filesystems should use to get at their own inodes @@ -527,7 +527,7 @@ static inline struct inode *d_inode(const struct dentry *dentry) */ static inline struct inode *d_inode_rcu(const struct dentry *dentry) { - return ACCESS_ONCE(dentry->d_inode); + return READ_ONCE(dentry->d_inode); } /** -- 1.9.1