From 66702eb59064f1077e89cce8e7e3cd48ec4b486c Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Mon, 23 Oct 2017 14:07:14 -0700 Subject: locking/atomics, fs/dcache: Convert ACCESS_ONCE() to READ_ONCE()/WRITE_ONCE() 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 Signed-off-by: Paul E. McKenney Cc: Al Viro Cc: Andrew Morton Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: davem@davemloft.net Cc: linux-arch@vger.kernel.org Cc: mpe@ellerman.id.au Cc: shuah@kernel.org Cc: snitzer@redhat.com Cc: thor.thayer@linux.intel.com Cc: tj@kernel.org Cc: will.deacon@arm.com Link: http://lkml.kernel.org/r/1508792849-3115-4-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar --- fs/dcache.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-) (limited to 'fs/dcache.c') diff --git a/fs/dcache.c b/fs/dcache.c index 34c852af215c..bcc9f6981569 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 @@ restart: 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 @@ restart: } /* Global root? */ if (mnt != parent) { - dentry = ACCESS_ONCE(mnt->mnt_mountpoint); + dentry = READ_ONCE(mnt->mnt_mountpoint); mnt = parent; vfsmnt = &mnt->mnt; continue; -- cgit v1.2.3-59-g8ed1b