netdev - [PATCH net-next 06/36] can: gw: use call_rcu() instead of costly synchronize

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Message-Id: <20220224082726.3000007-7-mkl@pengutronix.de>
Date:   Thu, 24 Feb 2022 09:26:56 +0100
From:   Marc Kleine-Budde <mkl@...gutronix.de>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, kuba@...nel.org, linux-can@...r.kernel.org,
        kernel@...gutronix.de, Eric Dumazet <edumazet@...gle.com>,
        Oliver Hartkopp <socketcan@...tkopp.net>,
        Marc Kleine-Budde <mkl@...gutronix.de>
Subject: [PATCH net-next 06/36] can: gw: use call_rcu() instead of costly synchronize_rcu()

From: Eric Dumazet <edumazet@...gle.com>

Commit fb8696ab14ad ("can: gw: synchronize rcu operations
before removing gw job entry") added three synchronize_rcu() calls
to make sure one rcu grace period was observed before freeing
a "struct cgw_job" (which are tiny objects).

This should be converted to call_rcu() to avoid adding delays
in device / network dismantles.

Use the rcu_head that was already in struct cgw_job,
not yet used.

Link: https://lore.kernel.org/all/20220207190706.1499190-1-eric.dumazet@gmail.com
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Oliver Hartkopp <socketcan@...tkopp.net>
Tested-by: Oliver Hartkopp <socketcan@...tkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
---
 net/can/gw.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/net/can/gw.c b/net/can/gw.c
index 24221352e059..1ea4cc527db3 100644
--- a/net/can/gw.c
+++ b/net/can/gw.c
@@ -577,6 +577,13 @@ static inline void cgw_unregister_filter(struct net *net, struct cgw_job *gwj)
 			  gwj->ccgw.filter.can_mask, can_can_gw_rcv, gwj);
 }
 
+static void cgw_job_free_rcu(struct rcu_head *rcu_head)
+{
+	struct cgw_job *gwj = container_of(rcu_head, struct cgw_job, rcu);
+
+	kmem_cache_free(cgw_cache, gwj);
+}
+
 static int cgw_notifier(struct notifier_block *nb,
 			unsigned long msg, void *ptr)
 {
@@ -596,8 +603,7 @@ static int cgw_notifier(struct notifier_block *nb,
 			if (gwj->src.dev == dev || gwj->dst.dev == dev) {
 				hlist_del(&gwj->list);
 				cgw_unregister_filter(net, gwj);
-				synchronize_rcu();
-				kmem_cache_free(cgw_cache, gwj);
+				call_rcu(&gwj->rcu, cgw_job_free_rcu);
 			}
 		}
 	}
@@ -1155,8 +1161,7 @@ static void cgw_remove_all_jobs(struct net *net)
 	hlist_for_each_entry_safe(gwj, nx, &net->can.cgw_list, list) {
 		hlist_del(&gwj->list);
 		cgw_unregister_filter(net, gwj);
-		synchronize_rcu();
-		kmem_cache_free(cgw_cache, gwj);
+		call_rcu(&gwj->rcu, cgw_job_free_rcu);
 	}
 }
 
@@ -1224,8 +1229,7 @@ static int cgw_remove_job(struct sk_buff *skb, struct nlmsghdr *nlh,
 
 		hlist_del(&gwj->list);
 		cgw_unregister_filter(net, gwj);
-		synchronize_rcu();
-		kmem_cache_free(cgw_cache, gwj);
+		call_rcu(&gwj->rcu, cgw_job_free_rcu);
 		err = 0;
 		break;
 	}
-- 
2.34.1