md-cluster: fix deadlock issue on message lock
There is problem with previous communication mechanism, and we got below
deadlock scenario with cluster which has 3 nodes.
Sender Receiver Receiver
token(EX)
message(EX)
writes message
downconverts message(CR)
requests ack(EX)
get message(CR) gets message(CR)
reads message reads message
requests EX on message requests EX on message
To fix this problem, we do the following changes:
1. the sender downconverts MESSAGE to CW rather than CR.
2. and the receiver request PR lock not EX lock on message.
And in case we failed to down-convert EX to CW on message, it is better to
unlock message otherthan still hold the lock.
Reviewed-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Signed-off-by: Lidong Zhong <ldzhong@suse.com>
Signed-off-by: Guoqing Jiang <gqjiang@suse.com>
Signed-off-by: NeilBrown <neilb@suse.com>
diff --git a/Documentation/md-cluster.txt b/Documentation/md-cluster.txt
index de1af7d..1b79436 100644
--- a/Documentation/md-cluster.txt
+++ b/Documentation/md-cluster.txt
@@ -91,7 +91,7 @@
this message inappropriate or redundant.
3. sender write LVB.
- sender down-convert MESSAGE from EX to CR
+ sender down-convert MESSAGE from EX to CW
sender try to get EX of ACK
[ wait until all receiver has *processed* the MESSAGE ]
@@ -112,7 +112,7 @@
sender down-convert ACK from EX to CR
sender release MESSAGE
sender release TOKEN
- receiver upconvert to EX of MESSAGE
+ receiver upconvert to PR of MESSAGE
receiver get CR of ACK
receiver release MESSAGE