Btrfs: barrier before waitqueue_active

We need a barrir before calling waitqueue_active otherwise we will miss
wakeups.  So in places that do atomic_dec(); then atomic_read() use
atomic_dec_return() which imply a memory barrier (see memory-barriers.txt)
and then add an explicit memory barrier everywhere else that need them.
Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>

1 files changed, 4 insertions, 3 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index a7ad8fc8dc53..dd86a5d88428 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -754,9 +754,7 @@ static void run_one_async_done(struct btrfs_work *work)
         limit = btrfs_async_submit_limit(fs_info);
         limit = limit * 2 / 3;
 
-        atomic_dec(&fs_info->nr_async_submits);
-
-        if (atomic_read(&fs_info->nr_async_submits) < limit &&
+        if (atomic_dec_return(&fs_info->nr_async_submits) < limit &&
             waitqueue_active(&fs_info->async_submit_wait))
                 wake_up(&fs_info->async_submit_wait);
 
@@ -3783,14 +3781,17 @@ int btrfs_cleanup_transaction(struct btrfs_root *root)
                 /* FIXME: cleanup wait for commit */
                 t->in_commit = 1;
                 t->blocked = 1;
+                smp_mb();
                 if (waitqueue_active(&root->fs_info->transaction_blocked_wait))
                         wake_up(&root->fs_info->transaction_blocked_wait);
 
                 t->blocked = 0;
+                smp_mb();
                 if (waitqueue_active(&root->fs_info->transaction_wait))
                         wake_up(&root->fs_info->transaction_wait);
 
                 t->commit_done = 1;
+                smp_mb();
                 if (waitqueue_active(&t->commit_wait))
                         wake_up(&t->commit_wait);