linux-kernel - [PATCH 5.17 081/140] RDMA/irdma: Reduce iWARP QP destroy time

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Date:   Tue, 10 May 2022 15:07:51 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Shiraz Saleem <shiraz.saleem@...el.com>,
        Jason Gunthorpe <jgg@...dia.com>
Subject: [PATCH 5.17 081/140] RDMA/irdma: Reduce iWARP QP destroy time

From: Shiraz Saleem <shiraz.saleem@...el.com>

commit 2df6d895907b2f5dfbc558cbff7801bba82cb3cc upstream.

QP destroy is synchronous and waits for its refcnt to be decremented in
irdma_cm_node_free_cb (for iWARP) which fires after the RCU grace period
elapses.

Applications running a large number of connections are exposed to high
wait times on destroy QP for events like SIGABORT.

The long pole for this wait time is the firing of the call_rcu callback
during a CM node destroy which can be slow. It holds the QP reference
count and blocks the destroy QP from completing.

call_rcu only needs to make sure that list walkers have a reference to the
cm_node object before freeing it and thus need to wait for grace period
elapse. The rest of the connection teardown in irdma_cm_node_free_cb is
moved out of the grace period wait in irdma_destroy_connection. Also,
replace call_rcu with a simple kfree_rcu as it just needs to do a kfree on
the cm_node

Fixes: 146b9756f14c ("RDMA/irdma: Add connection manager")
Link: https://lore.kernel.org/r/20220425181703.1634-3-shiraz.saleem@intel.com
Signed-off-by: Shiraz Saleem <shiraz.saleem@...el.com>
Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/infiniband/hw/irdma/cm.c |   10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

--- a/drivers/infiniband/hw/irdma/cm.c
+++ b/drivers/infiniband/hw/irdma/cm.c
@@ -2305,10 +2305,8 @@ err:
 	return NULL;
 }

-static void irdma_cm_node_free_cb(struct rcu_head *rcu_head)
+static void irdma_destroy_connection(struct irdma_cm_node *cm_node)
 {
-	struct irdma_cm_node *cm_node =
-			    container_of(rcu_head, struct irdma_cm_node, rcu_head);
 	struct irdma_cm_core *cm_core = cm_node->cm_core;
 	struct irdma_qp *iwqp;
 	struct irdma_cm_info nfo;
@@ -2356,7 +2354,6 @@ static void irdma_cm_node_free_cb(struct
 	}

 	cm_core->cm_free_ah(cm_node);
-	kfree(cm_node);
 }

 /**
@@ -2384,8 +2381,9 @@ void irdma_rem_ref_cm_node(struct irdma_

 	spin_unlock_irqrestore(&cm_core->ht_lock, flags);

-	/* wait for all list walkers to exit their grace period */
-	call_rcu(&cm_node->rcu_head, irdma_cm_node_free_cb);
+	irdma_destroy_connection(cm_node);
+
+	kfree_rcu(cm_node, rcu_head);
 }

 /**