btrfs: Replace ACCESS_ONCE with (READ|WRITE)_ONCE

Commit Message

Nikolay Borisov Dec. 26, 2016, 11:08 a.m. UTC

Use the newer and standardized functions when performing volatile
accesses. Following text is taken from 4d3199e4ca8e
("locking: Remove ACCESS_ONCE() usage") :

    ACCESS_ONCE() does not work reliably on non-scalar types.
    For example gcc 4.6 and 4.7 might remove the volatile tag
    for such accesses during the SRA (scalar replacement of
    aggregates) step:
	https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145

Signed-off-by: Nikolay Borisov <[e-mail]>
---
 fs/btrfs/delayed-inode.c |  4 ++--
 fs/btrfs/super.c         |  2 +-
 fs/btrfs/transaction.c   | 10 +++++-----
 fs/btrfs/tree-log.h      |  4 ++--
 4 files changed, 10 insertions(+), 10 deletions(-)

Comments

David Sterba Jan. 2, 2017, 3:16 p.m. UTC | #1

On Mon, Dec 26, 2016 at 01:08:09PM +0200, Nikolay Borisov wrote:
> Use the newer and standardized functions when performing volatile
> accesses. Following text is taken from 4d3199e4ca8e
> ("locking: Remove ACCESS_ONCE() usage") :
> 
>     ACCESS_ONCE() does not work reliably on non-scalar types.
>     For example gcc 4.6 and 4.7 might remove the volatile tag
>     for such accesses during the SRA (scalar replacement of
>     aggregates) step:
> 	https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145
> 
> Signed-off-by: Nikolay Borisov <[e-mail]>

A patch fort that has been sent and queued already,
https://patchwork.kernel.org/patch/9476137/
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Patch

diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index 80982a83c9fd..353e40fceba8 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -79,7 +79,7 @@  static struct btrfs_delayed_node *btrfs_get_delayed_node(struct inode *inode)
 	u64 ino = btrfs_ino(inode);
 	struct btrfs_delayed_node *node;
 
-	node = ACCESS_ONCE(btrfs_inode->delayed_node);
+	node = READ_ONCE(btrfs_inode->delayed_node);
 	if (node) {
 		atomic_inc(&node->refs);
 		return node;
@@ -1292,7 +1292,7 @@  void btrfs_remove_delayed_node(struct inode *inode)
 {
 	struct btrfs_delayed_node *delayed_node;
 
-	delayed_node = ACCESS_ONCE(BTRFS_I(inode)->delayed_node);
+	delayed_node = READ_ONCE(BTRFS_I(inode)->delayed_node);
 	if (!delayed_node)
 		return;
 
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index b5ae7d3d1896..93ed29c2a38b 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -265,7 +265,7 @@  void __btrfs_abort_transaction(struct btrfs_trans_handle *trans,
 		           function, line, errstr);
 		return;
 	}
-	ACCESS_ONCE(trans->transaction->aborted) = errno;
+	WRITE_ONCE(trans->transaction->aborted, errno);
 	/* Wake up anybody who may be waiting on this transaction */
 	wake_up(&fs_info->transaction_wait);
 	wake_up(&fs_info->transaction_blocked_wait);
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 0e0508f488b2..bd2890c2c9d3 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -866,14 +866,14 @@  static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
 
 	if (lock && !atomic_read(&info->open_ioctl_trans) &&
 	    should_end_transaction(trans) &&
-	    ACCESS_ONCE(cur_trans->state) == TRANS_STATE_RUNNING) {
+	    READ_ONCE(cur_trans->state) == TRANS_STATE_RUNNING) {
 		spin_lock(&info->trans_lock);
 		if (cur_trans->state == TRANS_STATE_RUNNING)
 			cur_trans->state = TRANS_STATE_BLOCKED;
 		spin_unlock(&info->trans_lock);
 	}
 
-	if (lock && ACCESS_ONCE(cur_trans->state) == TRANS_STATE_BLOCKED) {
+	if (lock && READ_ONCE(cur_trans->state) == TRANS_STATE_BLOCKED) {
 		if (throttle)
 			return btrfs_commit_transaction(trans);
 		else
@@ -1940,7 +1940,7 @@  int btrfs_commit_transaction(struct btrfs_trans_handle *trans)
 	int ret;
 
 	/* Stop the commit early if ->aborted is set */
-	if (unlikely(ACCESS_ONCE(cur_trans->aborted))) {
+	if (unlikely(READ_ONCE(cur_trans->aborted))) {
 		ret = cur_trans->aborted;
 		btrfs_end_transaction(trans);
 		return ret;
@@ -2080,7 +2080,7 @@  int btrfs_commit_transaction(struct btrfs_trans_handle *trans)
 		   atomic_read(&cur_trans->num_writers) == 1);
 
 	/* ->aborted might be set after the previous check, so check it */
-	if (unlikely(ACCESS_ONCE(cur_trans->aborted))) {
+	if (unlikely(READ_ONCE(cur_trans->aborted))) {
 		ret = cur_trans->aborted;
 		goto scrub_continue;
 	}
@@ -2194,7 +2194,7 @@  int btrfs_commit_transaction(struct btrfs_trans_handle *trans)
 	 * The tasks which save the space cache and inode cache may also
 	 * update ->aborted, check it.
 	 */
-	if (unlikely(ACCESS_ONCE(cur_trans->aborted))) {
+	if (unlikely(READ_ONCE(cur_trans->aborted))) {
 		ret = cur_trans->aborted;
 		mutex_unlock(&fs_info->tree_log_mutex);
 		mutex_unlock(&fs_info->reloc_mutex);
diff --git a/fs/btrfs/tree-log.h b/fs/btrfs/tree-log.h
index ab858e31ccbc..127eae01bb1b 100644
--- a/fs/btrfs/tree-log.h
+++ b/fs/btrfs/tree-log.h
@@ -48,13 +48,13 @@  static inline void btrfs_init_log_ctx(struct btrfs_log_ctx *ctx,
 static inline void btrfs_set_log_full_commit(struct btrfs_fs_info *fs_info,
 					     struct btrfs_trans_handle *trans)
 {
-	ACCESS_ONCE(fs_info->last_trans_log_full_commit) = trans->transid;
+	WRITE_ONCE(fs_info->last_trans_log_full_commit, trans->transid);
 }
 
 static inline int btrfs_need_log_full_commit(struct btrfs_fs_info *fs_info,
 					     struct btrfs_trans_handle *trans)
 {
-	return ACCESS_ONCE(fs_info->last_trans_log_full_commit) ==
+	return READ_ONCE(fs_info->last_trans_log_full_commit) ==
 		trans->transid;
 }