RDMA/iwcm: Use a default listen backlog if needed

If the user creates a listening cm_id with backlog of 0 the IWCM ends
up not allowing any connection requests at all.  The correct behavior
is for the IWCM to pick a default value if the user backlog parameter
is zero.

Lustre from version 1.8.8 onward uses a backlog of 0, which breaks
iwarp support without this fix.

Signed-off-by: Steve Wise <swise@opengridcomputing.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Roland Dreier <roland@purestorage.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/drivers/infiniband/core/iwcm.c b/drivers/infiniband/core/iwcm.c
index 3d2e489ab732..ff9163dc1596 100644
--- a/drivers/infiniband/core/iwcm.c
+++ b/drivers/infiniband/core/iwcm.c
@@ -46,6 +46,7 @@
 #include <linux/completion.h>
 #include <linux/slab.h>
 #include <linux/module.h>
+#include <linux/sysctl.h>
 
 #include <rdma/iw_cm.h>
 #include <rdma/ib_addr.h>
@@ -65,6 +66,20 @@ struct iwcm_work {
         struct list_head free_list;
 };
 
+static unsigned int default_backlog = 256;
+
+static struct ctl_table_header *iwcm_ctl_table_hdr;
+static struct ctl_table iwcm_ctl_table[] = {
+        {
+                .procname       = "default_backlog",
+                .data           = &default_backlog,
+                .maxlen         = sizeof(default_backlog),
+                .mode           = 0644,
+                .proc_handler   = proc_dointvec,
+        },
+        { }
+};
+
 /*
  * The following services provide a mechanism for pre-allocating iwcm_work
  * elements.  The design pre-allocates them  based on the cm_id type:
@@ -425,6 +440,9 @@ int iw_cm_listen(struct iw_cm_id *cm_id, int backlog)
 
         cm_id_priv = container_of(cm_id, struct iwcm_id_private, id);
 
+        if (!backlog)
+                backlog = default_backlog;
+
         ret = alloc_work_entries(cm_id_priv, backlog);
         if (ret)
                 return ret;
@@ -1030,11 +1048,20 @@ static int __init iw_cm_init(void)
         if (!iwcm_wq)
                 return -ENOMEM;
 
+        iwcm_ctl_table_hdr = register_net_sysctl(&init_net, "net/iw_cm",
+                                                 iwcm_ctl_table);
+        if (!iwcm_ctl_table_hdr) {
+                pr_err("iw_cm: couldn't register sysctl paths\n");
+                destroy_workqueue(iwcm_wq);
+                return -ENOMEM;
+        }
+
         return 0;
 }
 
 static void __exit iw_cm_cleanup(void)
 {
+        unregister_net_sysctl_table(iwcm_ctl_table_hdr);
         destroy_workqueue(iwcm_wq);
 }