On 09/04/2016 07:24 PM, NeilBrown wrote:

On Sun, Sep 04 2016, Guoqing Jiang wrote:

quoted

The md-cluster is compiled as module by default,
if it is compiled by built-in way, then we can't
make md-cluster works.

[64782.630008] md/raid1:md127: active with 2 out of 2 mirrors
[64782.630528] md-cluster module not found.
[64782.630530] md127: Could not setup cluster service (-2)

Fixes: edb39c9 ("Introduce md_cluster_operations to handle cluster functions")
Cc: stable@vger.kernel.org # v4.1+

The above results in you sending email to
    stable@vger.kernel.org#v4.1+
which is not a valid address.

The correct form for comments in email address is to use parentheses.
e.g.
    Cc: stable@vger.kernel.org (v4.1+)

Thanks for correct it!

quoted

Cc: NeilBrown <redacted>
Reported-by: Marc Smith <redacted>
Signed-off-by: Guoqing Jiang <redacted>
---
Changes:
1. call try_module_get if md_cluster_ops is already set,
otherwise try_module_get/module_put are unbalanced.

  drivers/md/md.c | 14 +++++---------
  1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 67642ba..6ac5abe 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c

@@ -7610,16 +7610,12 @@ EXPORT_SYMBOL(unregister_md_cluster_operations);
  
  int md_setup_cluster(struct mddev *mddev, int nodes)
  {
-	int err;
-
-	err = request_module("md-cluster");
-	if (err) {
-		pr_err("md-cluster module not found.\n");
-		return -ENOENT;
-	}
-
+	if (!md_cluster_ops)
+		request_module("md-cluster");
  	spin_lock(&pers_lock);
-	if (!md_cluster_ops || !try_module_get(md_cluster_mod)) {
+	/* ensure module won't be unloaded */
+	if (!try_module_get(md_cluster_mod)) {

Why did you drop the "!md_cluster_ops" test?

What happens if the md-cluster module cannot be loaded?
md_cluster_ops will be NULL and md_cluster_mod will be NULL.
try_module_get(NULL) succeeds, so with this patch md_setup_cluster()
will succeed if the module is needed but fails to load.

Yes, I just find try_module_get(NULL) could return true, it seems not
correct for the return value, maybe it need to be changed to:

             return module ? ret : false;

Anyway, I will send v3 with add "!md_cluster_ops" test back.

Thanks,
Guoqing