From: Mark Rutland <mark.rutland@xxxxxxx>
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 <mark.rutland@xxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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 f90141387f01..f283cd31a491 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 ed1a7cf6923a..1d8f5818f647 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);
}
/**
--
2.5.2
