netdev - [PATCH net-next] net/sysctl: avoid two synchronize

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Message-Id: <20220225161855.489923-1-eric.dumazet@gmail.com>
Date:   Fri, 25 Feb 2022 08:18:55 -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>
Subject: [PATCH net-next] net/sysctl: avoid two synchronize_rcu() calls

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

Both rps_sock_flow_sysctl() and flow_limit_cpu_sysctl()
are using synchronize_rcu() right before freeing memory
either by vfree() or kfree()

They can switch to kvfree_rcu(ptr) and kfree_rcu(ptr) to benefit
from asynchronous mode, instead of blocking the current thread.

Note that kvfree_rcu(ptr) and kfree_rcu(ptr) eventually can
have to use synchronize_rcu() in some memory pressure cases.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/sysctl_net_core.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index dbeb8ecbcd98f0aa6c02c650f925b05faf23ecad..7123fe7feeac634023d4e73247db0a20e3fcc383 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -103,8 +103,7 @@ static int rps_sock_flow_sysctl(struct ctl_table *table, int write,
 			if (orig_sock_table) {
 				static_branch_dec(&rps_needed);
 				static_branch_dec(&rfs_needed);
-				synchronize_rcu();
-				vfree(orig_sock_table);
+				kvfree_rcu(orig_sock_table);
 			}
 		}
 	}
@@ -142,8 +141,7 @@ static int flow_limit_cpu_sysctl(struct ctl_table *table, int write,
 				     lockdep_is_held(&flow_limit_update_mutex));
 			if (cur && !cpumask_test_cpu(i, mask)) {
 				RCU_INIT_POINTER(sd->flow_limit, NULL);
-				synchronize_rcu();
-				kfree(cur);
+				kfree_rcu(cur);
 			} else if (!cur && cpumask_test_cpu(i, mask)) {
 				cur = kzalloc_node(len, GFP_KERNEL,
 						   cpu_to_node(i));
-- 
2.35.1.574.g5d30c73bfb-goog