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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Florian Westphal <fw@strlen.de>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 5.8 16/16] mptcp: free acked data before waiting for more memory
Date:   Fri, 11 Sep 2020 14:47:33 +0200
Message-Id: <20200911122500.382563283@linuxfoundation.org>
In-Reply-To: <20200911122459.585735377@linuxfoundation.org>
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From: Florian Westphal <fw@strlen.de>

[ Upstream commit 1cec170d458b1d18f6f1654ca84c0804a701c5ef ]

After subflow lock is dropped, more wmem might have been made available.

This fixes a deadlock in mptcp_connect.sh 'mmap' mode: wmem is exhausted.
But as the mptcp socket holds on to already-acked data (for retransmit)
no wakeup will occur.

Using 'goto restart' calls mptcp_clean_una(sk) which will free pages
that have been acked completely in the mean time.

Fixes: fb529e62d3f3 ("mptcp: break and restart in case mptcp sndbuf is full")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/mptcp/protocol.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -772,7 +772,6 @@ fallback:
 restart:
 	mptcp_clean_una(sk);
 
-wait_for_sndbuf:
 	__mptcp_flush_join_list(msk);
 	ssk = mptcp_subflow_get_send(msk);
 	while (!sk_stream_memory_free(sk) ||
@@ -873,7 +872,7 @@ wait_for_sndbuf:
 				 */
 				mptcp_set_timeout(sk, ssk);
 				release_sock(ssk);
-				goto wait_for_sndbuf;
+				goto restart;
 			}
 		}
 	}