From: David Sterba <dsterba@suse.com>
Date: Mon, 16 Feb 2015 18:39:00 +0000 (+0100)
Subject: btrfs: remove extra barrier before waitqueue_active
X-Git-Tag: v4.4-rc1~82^2~38^2~1
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=779adf0f647651f5a45eeee3442c881300ce989e;p=karo-tx-linux.git

btrfs: remove extra barrier before waitqueue_active

Removing barriers is scary, but a call to atomic_dec_and_test implies
a barrier, so we don't need to issue another one.

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

diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index d0deb4643502..63275594debd 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -229,7 +229,9 @@ int btrfs_pin_log_trans(struct btrfs_root *root)
 void btrfs_end_log_trans(struct btrfs_root *root)
 {
 	if (atomic_dec_and_test(&root->log_writers)) {
-		smp_mb();
+		/*
+		 * Implicit memory barrier after atomic_dec_and_test
+		 */
 		if (waitqueue_active(&root->log_writer_wait))
 			wake_up(&root->log_writer_wait);
 	}
@@ -2820,7 +2822,9 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans,
 
 	mutex_lock(&log_root_tree->log_mutex);
 	if (atomic_dec_and_test(&log_root_tree->log_writers)) {
-		smp_mb();
+		/*
+		 * Implicit memory barrier after atomic_dec_and_test
+		 */
 		if (waitqueue_active(&log_root_tree->log_writer_wait))
 			wake_up(&log_root_tree->log_writer_wait);
 	}