[PATCH RFC] RDMA/cm: add timeout to cm_destroy_id wait

[Manjunath Patil <manjunath.b.patil@xxxxxxxxxx>]

Add timeout to cm_destroy_id, so that userspace can trigger any data
collection that would help in analyzing the cause of delay in destroying
the cm_id.

New noinline function helps dtrace/ebpf programs to hook on to it.
Existing functionality isn't changed except triggering a probe-able new
function at every timeout interval.

We have seen cases where CM messages stuck with MAD layer (either due to
software bug or faulty HCA), leading to cm_id getting stuck in the
following call stack. This patch helps in resolving such issues faster.

kernel: ... INFO: task XXXX:56778 blocked for more than 120 seconds.
...
	Call Trace:
	__schedule+0x2bc/0x895
	schedule+0x36/0x7c
	schedule_timeout+0x1f6/0x31f
 	? __slab_free+0x19c/0x2ba
	wait_for_completion+0x12b/0x18a
	? wake_up_q+0x80/0x73
	cm_destroy_id+0x345/0x610 [ib_cm]
	ib_destroy_cm_id+0x10/0x20 [ib_cm]
	rdma_destroy_id+0xa8/0x300 [rdma_cm]
	ucma_destroy_id+0x13e/0x190 [rdma_ucm]
	ucma_write+0xe0/0x160 [rdma_ucm]
	__vfs_write+0x3a/0x16d
	vfs_write+0xb2/0x1a1
	? syscall_trace_enter+0x1ce/0x2b8
	SyS_write+0x5c/0xd3
	do_syscall_64+0x79/0x1b9
	entry_SYSCALL_64_after_hwframe+0x16d/0x0

Signed-off-by: Manjunath Patil <manjunath.b.patil@xxxxxxxxxx>
---
 drivers/infiniband/core/cm.c | 38 +++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/core/cm.c b/drivers/infiniband/core/cm.c
index ff58058aeadc..03f7b80efa77 100644
--- a/drivers/infiniband/core/cm.c
+++ b/drivers/infiniband/core/cm.c
@@ -34,6 +34,20 @@ MODULE_AUTHOR("Sean Hefty");
 MODULE_DESCRIPTION("InfiniBand CM");
 MODULE_LICENSE("Dual BSD/GPL");
 
+static unsigned long cm_destroy_id_wait_timeout_sec = 10;
+
+static struct ctl_table_header *cm_ctl_table_header;
+static struct ctl_table cm_ctl_table[] = {
+	{
+		.procname	= "destroy_id_wait_timeout_sec",
+		.data		= &cm_destroy_id_wait_timeout_sec,
+		.maxlen		= sizeof(cm_destroy_id_wait_timeout_sec),
+		.mode		= 0644,
+		.proc_handler	= proc_doulongvec_minmax,
+	},
+	{ }
+};
+
 static const char * const ibcm_rej_reason_strs[] = {
 	[IB_CM_REJ_NO_QP]			= "no QP",
 	[IB_CM_REJ_NO_EEC]			= "no EEC",
@@ -1025,10 +1039,20 @@ static void cm_reset_to_idle(struct cm_id_private *cm_id_priv)
 	}
 }
 
+static noinline void cm_destroy_id_wait_timeout(struct ib_cm_id *cm_id)
+{
+	struct cm_id_private *cm_id_priv;
+
+	cm_id_priv = container_of(cm_id, struct cm_id_private, id);
+	pr_err("%s: cm_id=%p timed out. state=%d refcnt=%d\n", __func__,
+	       cm_id, cm_id->state, refcount_read(&cm_id_priv->refcount));
+}
+
 static void cm_destroy_id(struct ib_cm_id *cm_id, int err)
 {
 	struct cm_id_private *cm_id_priv;
 	struct cm_work *work;
+	int ret;
 
 	cm_id_priv = container_of(cm_id, struct cm_id_private, id);
 	spin_lock_irq(&cm_id_priv->lock);
@@ -1135,7 +1159,14 @@ static void cm_destroy_id(struct ib_cm_id *cm_id, int err)
 
 	xa_erase(&cm.local_id_table, cm_local_id(cm_id->local_id));
 	cm_deref_id(cm_id_priv);
-	wait_for_completion(&cm_id_priv->comp);
+	do {
+		ret = wait_for_completion_timeout(&cm_id_priv->comp,
+						  msecs_to_jiffies(
+				cm_destroy_id_wait_timeout_sec * 1000));
+		if (!ret) /* timeout happened */
+			cm_destroy_id_wait_timeout(cm_id);
+	} while (!ret);
+
 	while ((work = cm_dequeue_work(cm_id_priv)) != NULL)
 		cm_free_work(work);
 
@@ -4505,6 +4536,10 @@ static int __init ib_cm_init(void)
 	ret = ib_register_client(&cm_client);
 	if (ret)
 		goto error3;
+	cm_ctl_table_header = register_net_sysctl(&init_net,
+						  "net/ib_cm", cm_ctl_table);
+	if (!cm_ctl_table_header)
+		pr_warn("ib_cm: couldn't register sysctl path, using default values\n");
 
 	return 0;
 error3:
@@ -4522,6 +4557,7 @@ static void __exit ib_cm_cleanup(void)
 		cancel_delayed_work(&timewait_info->work.work);
 	spin_unlock_irq(&cm.lock);
 
+	unregister_net_sysctl_table(cm_ctl_table_header);
 	ib_unregister_client(&cm_client);
 	destroy_workqueue(cm.wq);
 
-- 
2.31.1