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authorMark Rutland <mark.rutland@arm.com>2017-10-23 14:07:14 -0700
committerIngo Molnar <mingo@kernel.org>2017-10-25 11:00:57 +0200
commit66702eb59064f1077e89cce8e7e3cd48ec4b486c (patch)
treebba2d6a8321865a9d25816d3e334960572a52dfe /fs/dcache.c
parenteeafcc5a5925d0819dad462eac1d42fda5fbe36f (diff)
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 <mark.rutland@arm.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> 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 <mingo@kernel.org>
Diffstat (limited to 'fs/dcache.c')
-rw-r--r--fs/dcache.c18
1 files changed, 9 insertions, 9 deletions
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;