From: David Sterba <dsterba@suse.com>
Date: Sat, 10 Oct 2015 16:24:48 +0000 (+0200)
Subject: btrfs: add barrier for waitqueue_active in clear_btree_io_tree
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=b666a9cd993c6a49c4bf23a1ed476359c978f60b;p=linux-beck.git

btrfs: add barrier for waitqueue_active in clear_btree_io_tree

waitqueue_active should be preceded by a barrier, in this function we
don't need to call it all the time.

Signed-off-by: David Sterba <dsterba@suse.com>
---

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 74bc3338418b..e8e5b5a10719 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -82,6 +82,12 @@ void btrfs_put_transaction(struct btrfs_transaction *transaction)
 static void clear_btree_io_tree(struct extent_io_tree *tree)
 {
 	spin_lock(&tree->lock);
+	/*
+	 * Do a single barrier for the waitqueue_active check here, the state
+	 * of the waitqueue should not change once clear_btree_io_tree is
+	 * called.
+	 */
+	smp_mb();
 	while (!RB_EMPTY_ROOT(&tree->state)) {
 		struct rb_node *node;
 		struct extent_state *state;