src/paxos_lease.c

[David Teigland]

 src/paxos_lease.c |   22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

New commits:
commit 5be245a0c186d319b7572ca812a0067a48b420dc
Author: David Teigland <teigland(a)redhat.com&gt;
Date:   Tue Mar 1 16:12:31 2011 -0600

    sanlock: fix host_id expiration check
    
    When checking if another hostid has expired we cannot base
    it on the last disk renewal time from the other host, because
    the other host may not have time in sync.

diff --git a/src/paxos_lease.c b/src/paxos_lease.c
index 96e77cc..ee1fb75 100644
--- a/src/paxos_lease.c
+++ b/src/paxos_lease.c
@@ -606,6 +606,7 @@ int paxos_lease_acquire(struct token *token, int force GNUC_UNUSED,
 	struct leader_record new_leader;
 	struct leader_record host_id_leader;
 	struct paxos_dblock dblock;
+	time_t start;
 	uint64_t last_timestamp = 0;
 	int error;
 
@@ -634,6 +635,8 @@ int paxos_lease_acquire(struct token *token, int force GNUC_UNUSED,
 	log_token(token, "paxos_acquire check owner_id %llu",
 		  (unsigned long long)prev_leader.owner_id);
 
+	start = time(NULL);
+
 	while (1) {
 		error = host_id_leader_read(prev_leader.space_name,
 					    prev_leader.owner_id,
@@ -682,14 +685,31 @@ int paxos_lease_acquire(struct token *token, int force GNUC_UNUSED,
 
 		/* if the owner hasn't renewed its host_id lease for
 		   host_id_timeout_seconds then its watchdog should have fired
-		   by now */
+		   by now
+
+		   if we trust that the clocks are in sync among hosts, then this
+		   check could be: if (time(NULL) - host_id_leader.timestamp >
+		   to.host_id_timeout_seconds), but if the clocks are out of sync,
+		   this check would easily give two hosts the lease.
+
+		   N.B. we need to be careful about ever comparing local time(NULL)
+		   to a time value we read off disk from another node that may
+		   have different time. */
 
+		if (time(NULL) - start > to.host_id_timeout_seconds) {
+			log_token(token, "paxos_acquire host_id %llu expired %llu",
+				  (unsigned long long)prev_leader.owner_id,
+				  (unsigned long long)host_id_leader.timestamp);
+			goto run;
+		}
+#if 0
 		if (time(NULL) - host_id_leader.timestamp > to.host_id_timeout_seconds) {
 			log_token(token, "paxos_acquire host_id %llu expired %llu",
 				  (unsigned long long)prev_leader.owner_id,
 				  (unsigned long long)host_id_leader.timestamp);
 			goto run;
 		}
+#endif
 
 		/* the owner is renewing its host_id so it's alive */