From: David Sterba <dsterba@suse.com>
Date: Fri, 16 Mar 2018 01:39:40 +0000 (+0100)
Subject: btrfs: update barrier in should_cow_block
X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=d1980131ca7f0776542f776ceb777cd01eb983e2;p=openwrt%2Fstaging%2Fblogic.git

btrfs: update barrier in should_cow_block

Once there was a simple int force_cow that was used with the plain
barriers, and then converted to a bit, so we should use the appropriate
barrier helper.

Other variables in the complex if condition do not depend on a barrier,
so we should be fine in case the atomic barrier becomes a no-op.

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

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 7c8faeb868f4..a2c9d21176e2 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -1441,8 +1441,8 @@ static inline int should_cow_block(struct btrfs_trans_handle *trans,
 	if (btrfs_is_testing(root->fs_info))
 		return 0;
 
-	/* ensure we can see the force_cow */
-	smp_rmb();
+	/* Ensure we can see the FORCE_COW bit */
+	smp_mb__before_atomic();
 
 	/*
 	 * We do not need to cow a block if