sgi-xp: eliminate false detection of no heartbeat

After XPC has been up and running on multiple partitions for any length of
time, if XPC on one of the partitions is stopped and restarted (either by
a rmmod/insmod or a system restart), it is possible for the XPCs running
on the other partitions to falsely detect a lack of heartbeat from the XPC
that was just restarted.  This false detection will occur if the restarted
XPC comes up within the five-seconds preceding one of the other XPC's
heartbeat check (which occurs once every twenty seconds).

The detection of no heartbeat results in the detecting XPC deactivating
from the just restarted XPC.  The only remedy is to restart one of the
XPCs and hope that one doesn't hit this five-second window on any of the
other partitions.
Signed-off-by: NDean Nelson <dcn@sgi.com>
Signed-off-by: NRobin Holt <holt@sgi.com>
Cc: <stable@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/misc/sgi-xp/xpc_sn2.c

@@ -899,7 +899,7 @@ xpc_update_partition_info_sn2(struct xpc_partition *part, u8 remote_rp_version,
 	dev_dbg(xpc_part, "  remote_vars_pa = 0x%016lx\n",
 		part_sn2->remote_vars_pa);
 
-	part->last_heartbeat = remote_vars->heartbeat;
+	part->last_heartbeat = remote_vars->heartbeat - 1;
 	dev_dbg(xpc_part, "  last_heartbeat = 0x%016lx\n",
 		part->last_heartbeat);