f2fs: fix out-of-order execution in f2fs_issue_flush

In f2fs_issue_flush, due to out-of-order execution of CPU, wake_up can
be called before we insert issue_list, result in long latency of
wait_for_completion. Fix this by adding smp_mb() to force the order of
related codes.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index e3922f9..be1c49b 100644 (file)
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -549,7 +549,10 @@ int f2fs_issue_flush(struct f2fs_sb_info *sbi)
        atomic_inc(&fcc->issing_flush);
        llist_add(&cmd.llnode, &fcc->issue_list);
 
-       if (!fcc->dispatch_list)
+       /* update issue_list before we wake up issue_flush thread */
+       smp_mb();
+
+       if (waitqueue_active(&fcc->flush_wait_queue))
                wake_up(&fcc->flush_wait_queue);
 
        if (fcc->f2fs_issue_flush) {