netdev - [PATCH net-next 5/5] mptcp: make the locking tx schema more readable

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Date:   Thu, 26 Aug 2021 17:44:54 -0700
From:   Mat Martineau <mathew.j.martineau@...ux.intel.com>
To:     netdev@...r.kernel.org
Cc:     Paolo Abeni <pabeni@...hat.com>, davem@...emloft.net,
        kuba@...nel.org, matthieu.baerts@...sares.net,
        mptcp@...ts.linux.dev, Florian Westphal <fw@...len.de>,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>
Subject: [PATCH net-next 5/5] mptcp: make the locking tx schema more readable

From: Paolo Abeni <pabeni@...hat.com>

Florian noted the locking schema used by __mptcp_push_pending()
is hard to follow, let's add some more descriptive comments
and drop an unneeded and confusing check.

Suggested-by: Florian Westphal <fw@...len.de>
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@...ux.intel.com>
---
 net/mptcp/protocol.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 1a408395e78f..ade648c3512b 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1515,15 +1515,19 @@ void __mptcp_push_pending(struct sock *sk, unsigned int flags)
 			mptcp_flush_join_list(msk);
 			ssk = mptcp_subflow_get_send(msk);
 
-			/* try to keep the subflow socket lock across
-			 * consecutive xmit on the same socket
+			/* First check. If the ssk has changed since
+			 * the last round, release prev_ssk
 			 */
 			if (ssk != prev_ssk && prev_ssk)
 				mptcp_push_release(sk, prev_ssk, &info);
 			if (!ssk)
 				goto out;
 
-			if (ssk != prev_ssk || !prev_ssk)
+			/* Need to lock the new subflow only if different
+			 * from the previous one, otherwise we are still
+			 * helding the relevant lock
+			 */
+			if (ssk != prev_ssk)
 				lock_sock(ssk);
 
 			/* keep it simple and always provide a new skb for the
-- 
2.33.0