linux-kernel - [PATCH net-next v2] mptcp: remove unneeded lock when listing scheds

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Message-Id: <20241104-net-next-mptcp-sched-unneeded-lock-v2-1-2ccc1e0c750c@kernel.org>
Date: Mon, 04 Nov 2024 13:43:47 +0100
From: "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
To: mptcp@...ts.linux.dev, Mat Martineau <martineau@...nel.org>, 
 Geliang Tang <geliang@...nel.org>, "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
 "Matthieu Baerts (NGI0)" <matttbe@...nel.org>
Subject: [PATCH net-next v2] mptcp: remove unneeded lock when listing
 scheds

mptcp_get_available_schedulers() needs to iterate over the schedulers'
list only to read the names: it doesn't modify anything there.

In this case, it is enough to hold the RCU read lock, no need to combine
this with the associated spin lock as it was done since its introduction
in commit 73c900aa3660 ("mptcp: add net.mptcp.available_schedulers").

Suggested-by: Paolo Abeni <pabeni@...hat.com>
Reviewed-by: Geliang Tang <geliang@...nel.org>
Reviewed-by: Simon Horman <horms@...nel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@...nel.org>
---
v2:
 - Rebased on top of net-next instead of net, same code.
 - Removed the 'Fixes' tag, add Simon's RvB tag.
 - Link to v1: https://lore.kernel.org/20241021-net-mptcp-sched-lock-v1-2-637759cf061c@kernel.org
---
 net/mptcp/sched.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/net/mptcp/sched.c b/net/mptcp/sched.c
index 78ed508ebc1b8dd9f0e020cca1bdd86f24f0afeb..df7dbcfa3b71370cc4d7e4e4f16cc1e41a50dddf 100644
--- a/net/mptcp/sched.c
+++ b/net/mptcp/sched.c
@@ -60,7 +60,6 @@ void mptcp_get_available_schedulers(char *buf, size_t maxlen)
 	size_t offs = 0;

 	rcu_read_lock();
-	spin_lock(&mptcp_sched_list_lock);
 	list_for_each_entry_rcu(sched, &mptcp_sched_list, list) {
 		offs += snprintf(buf + offs, maxlen - offs,
 				 "%s%s",
@@ -69,7 +68,6 @@ void mptcp_get_available_schedulers(char *buf, size_t maxlen)
 		if (WARN_ON_ONCE(offs >= maxlen))
 			break;
 	}
-	spin_unlock(&mptcp_sched_list_lock);
 	rcu_read_unlock();
 }

---
base-commit: ecf99864ea6b1843773589a935bb026951bf12dd
change-id: 20241104-net-next-mptcp-sched-unneeded-lock-006eb3fc96b7

Best regards,
-- 
Matthieu Baerts (NGI0) <matttbe@...nel.org>