Miao Xie
2014-Feb-20 10:08 UTC
[PATCH 1/9] 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> --- fs/btrfs/tree-log.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 deletions(-) diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c index 7c449c6..5a4e10b 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); -- 1.8.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html