Commit 66702eb5 authored by Mark Rutland's avatar Mark Rutland Committed by Ingo Molnar
Browse files

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: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarPaul 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: default avatarIngo Molnar <mingo@kernel.org>
parent eeafcc5a

fs/dcache.c

+9 −9
Original line number Diff line number Diff line
@@ -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;

include/linux/dcache.h

+2 −2
Original line number Diff line number Diff line
@@ -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);

}



/**

CRA Git | Maintained and supported by SUSTech CRA and CCSE