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

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Date:   Mon,  7 Feb 2022 11:07:06 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Oliver Hartkopp <socketcan@...tkopp.net>
Subject: [PATCH net-next] 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.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Oliver Hartkopp <socketcan@...tkopp.net>
---
 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 d8861e862f157aec36c417b71eb7e8f59bd064b9..20e74fe7d0906dccc65732b8f9e7e14e2d1192c3 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;
 	}
-- 
2.35.0.263.gb82422642f-goog