From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 02C0F158208; Tue, 9 Jul 2024 11:22:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720524158; cv=none; b=lmo9oKgUjsMMe/Ul9qbsqnL6nifvE8o5uE1gDMa2PjptqbZ7X7pWGp60vqDDnqN52iddJ5qWX3wIX1Tl/y7o3wCF2eWkD3VCjBVQ++ni7HjvEx2VSaIiUzI/RuXsAoh4VTr08rOx92PzNzajZ0KTeLedLDr5KAjav9QNKoTQ6sQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1720524158; c=relaxed/simple; bh=+xo/bblR2R2ENm7tnv9TnLZSknSbhaSO8ocEbv43WEk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=mFFDBsMqDk300Ul2od4KTAH5NWS7UrpHbNeP5DbRmWEV41talpr/LDz5AOYlh+HJTma4kZuwjqgBqR2fvRbtltVu6PqjVCADGXkO9U4kA23UWDXlC9AwciPI4ZveIav+5XBb7J9CYiElEpeC9UDoopi355EOt4SNKZ+ZVLdcXFo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=ztXuimAE; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="ztXuimAE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 75538C3277B; Tue, 9 Jul 2024 11:22:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1720524157; bh=+xo/bblR2R2ENm7tnv9TnLZSknSbhaSO8ocEbv43WEk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ztXuimAETekU9wWG4VqaMOtl9V6SUXRJ5Jl80PqSxgNdiRvZxe0cqQFEddd+cyCNI vpe/eu2KyPer21wI4WN1oJDjrifTbtN78VahvDaUGPRfwttawz6qEAK3yqlEbWJxpe gKaFYdilUhfc+16GfzxE5BMPuFIk37gyaiwm7WNU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Neal Cardwell , Yuchung Cheng , Eric Dumazet , "David S. Miller" , Sasha Levin Subject: [PATCH 6.9 089/197] UPSTREAM: tcp: fix DSACK undo in fast recovery to call tcp_try_to_open() Date: Tue, 9 Jul 2024 13:09:03 +0200 Message-ID: <20240709110712.410069115@linuxfoundation.org> X-Mailer: git-send-email 2.45.2 In-Reply-To: <20240709110708.903245467@linuxfoundation.org> References: <20240709110708.903245467@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Neal Cardwell [ Upstream commit a6458ab7fd4f427d4f6f54380453ad255b7fde83 ] In some production workloads we noticed that connections could sometimes close extremely prematurely with ETIMEDOUT after transmitting only 1 TLP and RTO retransmission (when we would normally expect roughly tcp_retries2 = TCP_RETR2 = 15 RTOs before a connection closes with ETIMEDOUT). >>From tracing we determined that these workloads can suffer from a scenario where in fast recovery, after some retransmits, a DSACK undo can happen at a point where the scoreboard is totally clear (we have retrans_out == sacked_out == lost_out == 0). In such cases, calling tcp_try_keep_open() means that we do not execute any code path that clears tp->retrans_stamp to 0. That means that tp->retrans_stamp can remain erroneously set to the start time of the undone fast recovery, even after the fast recovery is undone. If minutes or hours elapse, and then a TLP/RTO/RTO sequence occurs, then the start_ts value in retransmits_timed_out() (which is from tp->retrans_stamp) will be erroneously ancient (left over from the fast recovery undone via DSACKs). Thus this ancient tp->retrans_stamp value can cause the connection to die very prematurely with ETIMEDOUT via tcp_write_err(). The fix: we change DSACK undo in fast recovery (TCP_CA_Recovery) to call tcp_try_to_open() instead of tcp_try_keep_open(). This ensures that if no retransmits are in flight at the time of DSACK undo in fast recovery then we properly zero retrans_stamp. Note that calling tcp_try_to_open() is more consistent with other loss recovery behavior, since normal fast recovery (CA_Recovery) and RTO recovery (CA_Loss) both normally end when tp->snd_una meets or exceeds tp->high_seq and then in tcp_fastretrans_alert() the "default" switch case executes tcp_try_to_open(). Also note that by inspection this change to call tcp_try_to_open() implies at least one other nice bug fix, where now an ECE-marked DSACK that causes an undo will properly invoke tcp_enter_cwr() rather than ignoring the ECE mark. Fixes: c7d9d6a185a7 ("tcp: undo on DSACK during recovery") Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Sasha Levin --- net/ipv4/tcp_input.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 0953c915bb4de..77109976fe836 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -3074,7 +3074,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una, return; if (tcp_try_undo_dsack(sk)) - tcp_try_keep_open(sk); + tcp_try_to_open(sk, flag); tcp_identify_packet_loss(sk, ack_flag); if (icsk->icsk_ca_state != TCP_CA_Recovery) { -- 2.43.0