[Cluster-devel] dlm: Don't send callback to node making lock request when "try 1cb" fails

[Steven Whitehouse <swhiteho@redhat.com>]

When converting a lock, an lkb is in the granted state and also being used
to request a new state. In the case that the conversion was a "try 1cb"
type which has failed, and if the new state was incompatible with the old
state, a callback was being generated to the requesting node. This is
incorrect as callbacks should only be sent to all the other nodes holding
blocking locks. The requesting node should receive the normal (failed)
response to its "try 1cb" conversion request only.

This was discovered while debugging a performance problem on GFS2, however
this fix also speeds up GFS as well. In the GFS2 case the performance gain
is over 10x for cases of write activity to an inode whose glock is cached
on another, idle (wrt that glock) node.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Tested-by: Abhijith Das <adas@redhat.com>

diff --git a/fs/dlm/lock.c b/fs/dlm/lock.c
index 031dbe3..dae42e1 100644
--- a/fs/dlm/lock.c
+++ b/fs/dlm/lock.c
@@ -1846,6 +1846,8 @@ static void send_bast_queue(struct dlm_rsb *r, struct list_head *head,
 	struct dlm_lkb *gr;
 
 	list_for_each_entry(gr, head, lkb_statequeue) {
+		if (gr == lkb)
+			continue;
 		if (gr->lkb_bastfn && modes_require_bast(gr, lkb)) {
 			queue_bast(r, gr, lkb->lkb_rqmode);
 			gr->lkb_highbast = lkb->lkb_rqmode;