[PATCH dlm/tool] dlm_controld: send plock operations without resource lookup

From: David Teigland <[email protected]>

When plock_ownership mode is disabled, a plock operation read from
the kernel can be sent to all nodes immediately, without looking up
the local resource struct.  This is faster, and it avoids a bug in
cases where multiple threads in a process submit concurrent fcntl
lock ops on a file.

This bug occurs because create/free of the resource struct should
only be done in the context of ordered receive_plock cpg messages.
plock unlock results were being incorrectly returned based on the
non-existence of a struct resource checked in process_plocks (outside
of the ordered message context.)  In this case, the existence of the
resource struct was used to imply a lock state ("no locks"), which is
invalid to conclude outside of the message context.  The bug would
only appear in the unusual scenario where multiple threads in a
process are running concurrent fcntl lock operations on a file.

This fix does not address the problem when plock_ownership is enabled,
so warnings are added for the plock_ownership setting.
---
 dlm_controld/dlm_controld.8 | 2 ++
 dlm_controld/main.c         | 2 +-
 dlm_controld/plock.c        | 5 +++++
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/dlm_controld/dlm_controld.8 b/dlm_controld/dlm_controld.8
index d72ebb29..a607f73c 100644
--- a/dlm_controld/dlm_controld.8
+++ b/dlm_controld/dlm_controld.8
@@ -50,6 +50,8 @@ For default settings, see dlm_controld -h.
 .B --plock_ownership | -o
 0|1
         enable/disable plock ownership
+.br
+        (WARNING: do not enable if threads perform fcntl locking.)
 
 .B --drop_resources_time | -t
 .I int
diff --git a/dlm_controld/main.c b/dlm_controld/main.c
index a4beb312..d2dfe601 100644
--- a/dlm_controld/main.c
+++ b/dlm_controld/main.c
@@ -1860,7 +1860,7 @@ static void set_opt_defaults(void)
 	set_opt_default(plock_ownership_ind,
 			"plock_ownership", 'o', req_arg_bool,
 			0, NULL, 0, 0,
-			"enable/disable plock ownership");
+			"enable/disable plock ownership (do not enable if threads do fcntl locking)");
 
 	set_opt_default(drop_resources_time_ind,
 			"drop_resources_time", 't', req_arg_int,
diff --git a/dlm_controld/plock.c b/dlm_controld/plock.c
index 1944cd59..30cf61a5 100644
--- a/dlm_controld/plock.c
+++ b/dlm_controld/plock.c
@@ -1599,6 +1599,11 @@ void process_plocks(int ci)
 		plock_rate_delays = 0;
 	}
 
+	if (!opt(plock_ownership_ind)) {
+		send_plock(ls, NULL, &info);
+		return;
+	}
+
 	create = (info.optype == DLM_PLOCK_OP_UNLOCK) ? 0 : 1;
 
 	rv = find_resource(ls, info.number, create, &r);
-- 
2.43.0