Btrfs: use ACCESS_ONCE to prevent the optimize accesses to ->last_trans_log_full_commit

->last_trans_log_full_commit may be changed by the other tasks without lock,
so we need prevent the compiler from the optimize access just like
	tmp = fs_info->last_trans_log_full_commit
	if (tmp == ...)
		...

	<do something>

	if (tmp == ...)
		...

In fact, we need get the new value of ->last_trans_log_full_commit during
the second access. Fix it by ACCESS_ONCE().

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>

1 files changed, 10 insertions, 7 deletions

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 7c449c699bed..5a4e10b9ac3e 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -2375,14 +2375,14 @@ static int wait_log_commit(struct btrfs_trans_handle *trans,
                                 &wait, TASK_UNINTERRUPTIBLE);
                 mutex_unlock(&root->log_mutex);
 
-                if (root->fs_info->last_trans_log_full_commit !=
+                if (ACCESS_ONCE(root->fs_info->last_trans_log_full_commit) !=
                     trans->transid && root->log_transid < transid + 2 &&
                     atomic_read(&root->log_commit[index]))
                         schedule();
 
                 finish_wait(&root->log_commit_wait[index], &wait);
                 mutex_lock(&root->log_mutex);
-        } while (root->fs_info->last_trans_log_full_commit !=
+        } while (ACCESS_ONCE(root->fs_info->last_trans_log_full_commit) !=
                  trans->transid && root->log_transid < transid + 2 &&
                  atomic_read(&root->log_commit[index]));
         return 0;
@@ -2392,12 +2392,12 @@ static void wait_for_writer(struct btrfs_trans_handle *trans,
                             struct btrfs_root *root)
 {
         DEFINE_WAIT(wait);
-        while (root->fs_info->last_trans_log_full_commit !=
+        while (ACCESS_ONCE(root->fs_info->last_trans_log_full_commit) !=
                trans->transid && atomic_read(&root->log_writers)) {
                 prepare_to_wait(&root->log_writer_wait,
                                 &wait, TASK_UNINTERRUPTIBLE);
                 mutex_unlock(&root->log_mutex);
-                if (root->fs_info->last_trans_log_full_commit !=
+                if (ACCESS_ONCE(root->fs_info->last_trans_log_full_commit) !=
                     trans->transid && atomic_read(&root->log_writers))
                         schedule();
                 mutex_lock(&root->log_mutex);
@@ -2456,7 +2456,8 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
         }
 
         /* bail out if we need to do a full commit */
-        if (root->fs_info->last_trans_log_full_commit == trans->transid) {
+        if (ACCESS_ONCE(root->fs_info->last_trans_log_full_commit) ==
+            trans->transid) {
                 ret = -EAGAIN;
                 btrfs_free_logged_extents(log, log_transid);
                 mutex_unlock(&root->log_mutex);
@@ -2515,7 +2516,8 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
                         mutex_unlock(&log_root_tree->log_mutex);
                         goto out;
                 }
-                root->fs_info->last_trans_log_full_commit = trans->transid;
+                ACCESS_ONCE(root->fs_info->last_trans_log_full_commit) =
+                                                                trans->transid;
                 btrfs_wait_marked_extents(log, &log->dirty_log_pages, mark);
                 btrfs_free_logged_extents(log, log_transid);
                 mutex_unlock(&log_root_tree->log_mutex);
@@ -2547,7 +2549,8 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
          * now that we've moved on to the tree of log tree roots,
          * check the full commit flag again
          */
-        if (root->fs_info->last_trans_log_full_commit == trans->transid) {
+        if (ACCESS_ONCE(root->fs_info->last_trans_log_full_commit) ==
+            trans->transid) {
                 blk_finish_plug(&plug);
                 btrfs_wait_marked_extents(log, &log->dirty_log_pages, mark);
                 btrfs_free_logged_extents(log, log_transid);