[Cluster-devel] [PATCH 03/11] GFS2: Protect log tail calculations with inside locks

[Bob Peterson <rpeterso@redhat.com>]

This patch adjusts two functions related to the journal's log tail.
It essentially moves them inside the protective locks so they can't
be moved by another process. If the calculations aren't protected,
the log's tail may not be properly pulled, which eventually makes
it seem like there isn't enough room in the journal for more
transactions. This results in a hang where GFS2 repeatedly does
log flushes without making any progress or making any room.
---
 fs/gfs2/log.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/fs/gfs2/log.c b/fs/gfs2/log.c
index 536e7a6..18959de 100644
--- a/fs/gfs2/log.c
+++ b/fs/gfs2/log.c
@@ -277,11 +277,12 @@ static void gfs2_ail2_empty_one(struct gfs2_sbd *sdp, struct gfs2_trans *tr)
 static void ail2_empty(struct gfs2_sbd *sdp, unsigned int new_tail)
 {
 	struct gfs2_trans *tr, *safe;
-	unsigned int old_tail = sdp->sd_log_tail;
-	int wrap = (new_tail < old_tail);
-	int a, b, rm;
+	unsigned int old_tail;
+	int wrap, a, b, rm;
 
 	spin_lock(&sdp->sd_ail_lock);
+	old_tail = sdp->sd_log_tail;
+	wrap = (new_tail < old_tail);
 
 	list_for_each_entry_safe(tr, safe, &sdp->sd_ail2_list, tr_list) {
 		a = (old_tail <= tr->tr_first);
-- 
2.4.3