[Cluster-devel] [GFS2] Fix assert in log code

[Steven Whitehouse]

>From 3a46e3bef51f7a1feffafcac855c1b252fcc5877 Mon Sep 17 00:00:00 2001
From: Steven Whitehouse <swhiteho at redhat.com>
Date: Thu, 10 Jan 2008 14:49:43 +0000
Subject: [PATCH] [GFS2] Fix assert in log code

Although the values were all being calculated correctly, there was a
race in the assert due to the way it was using atomic variables. This
changes the value we assert on so that we get the same effect by testing
a different variable. This prevents the assert triggering when it shouldn't.

Signed-off-by: Steven Whitehouse <swhiteho at redhat.com>

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 40c51bf..6e6a104 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -749,7 +749,7 @@ void __gfs2_log_flush(struct gfs2_sbd *sdp, struct gfs2_glock *gl)
 static void log_refund(struct gfs2_sbd *sdp, struct gfs2_trans *tr)
 {
 	unsigned int reserved;
-	unsigned int old;
+	unsigned int unused;
 
 	gfs2_log_lock(sdp);
 
@@ -761,14 +761,11 @@ static void log_refund(struct gfs2_sbd *sdp, struct gfs2_trans *tr)
 	sdp->sd_log_commited_revoke += tr->tr_num_revoke - tr->tr_num_revoke_rm;
 	gfs2_assert_withdraw(sdp, ((int)sdp->sd_log_commited_revoke) >= 0);
 	reserved = calc_reserved(sdp);
-	old = atomic_read(&sdp->sd_log_blks_free);
-	atomic_add(tr->tr_reserved - (reserved - sdp->sd_log_blks_reserved),
-		   &sdp->sd_log_blks_free);
-
-	gfs2_assert_withdraw(sdp, atomic_read(&sdp->sd_log_blks_free) >= old);
+	unused = sdp->sd_log_blks_reserved - reserved + tr->tr_reserved;
+	gfs2_assert_withdraw(sdp, unused >= 0);
+	atomic_add(unused, &sdp->sd_log_blks_free);
 	gfs2_assert_withdraw(sdp, atomic_read(&sdp->sd_log_blks_free) <=
 			     sdp->sd_jdesc->jd_blocks);
-
 	sdp->sd_log_blks_reserved = reserved;
 
 	gfs2_log_unlock(sdp);
-- 
1.5.1.2