From: Chris Mason <chris.mason@fusionio.com>
Date: Wed, 25 Jul 2012 20:03:32 +0000 (-0400)
Subject: Btrfs: add a barrier before a waitqueue_active check
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=cd1cfc49153ba2bef247e500d8bd4d135193ece9;p=linux-beck.git

Btrfs: add a barrier before a waitqueue_active check

We were missing wakeups on the delayed ref waitqueue due
to races on waitqueue_active.

Signed-off-by: Chris Mason <chris.mason@fusionio.com>
---

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 44f06201f376..4e1b153b7c47 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -5294,6 +5294,7 @@ static noinline int check_ref_cleanup(struct btrfs_trans_handle *trans,
 	rb_erase(&head->node.rb_node, &delayed_refs->root);
 
 	delayed_refs->num_entries--;
+	smp_mb();
 	if (waitqueue_active(&root->fs_info->tree_mod_seq_wait))
 		wake_up(&root->fs_info->tree_mod_seq_wait);