From mboxrd@z Thu Jan 1 00:00:00 1970 From: maowenan Subject: Re: [PATCH 4.9-stable] tcp: add tcp_ooo_try_coalesce() helper Date: Fri, 10 Aug 2018 18:10:44 +0800 Message-ID: <13f2b820-37d6-cea0-ff75-889c81ab98f5@huawei.com> References: <1533373442.16128.123.camel@infradead.org> <1533373800-22712-1-git-send-email-dwmw@amazon.co.uk> <20180807132256.GH1904@kroah.com> <20e03726-c053-67a3-505a-7110be0f5d34@huawei.com> <20180809124726.GA9500@kroah.com> <1533819122.5775.12.camel@infradead.org> <1eb36303-c713-a517-735b-da1cd8343712@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Cc: , , , , , , , To: David Woodhouse , Greg KH Return-path: Received: from szxga05-in.huawei.com ([45.249.212.191]:10698 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727258AbeHJMkD (ORCPT ); Fri, 10 Aug 2018 08:40:03 -0400 In-Reply-To: <1eb36303-c713-a517-735b-da1cd8343712@huawei.com> Sender: netdev-owner@vger.kernel.org List-ID: On 2018/8/10 14:26, maowenan wrote: > > > On 2018/8/9 20:52, David Woodhouse wrote: >> On Thu, 2018-08-09 at 14:47 +0200, Greg KH wrote: >>> On Thu, Aug 09, 2018 at 08:37:13PM +0800, maowenan wrote: >>>> There are two patches in stable branch linux-4.4, but I have tested with below patches, and found that the cpu usage was very high. >>>> dc6ae4d tcp: detect malicious patterns in tcp_collapse_ofo_queue() >>>> 5fbec48 tcp: avoid collapses in tcp_prune_queue() if possible >>>> >>>> test results: >>>> with fix patch： 78.2% ksoftirqd >>>> no fix patch： 90% ksoftirqd >>>> >>>> there is %0 when no attack packets. >>>> >>>> so please help verify that fixed patches are enough in linux-stable 4.4. >>>> >>> >>> I do not know, I am not a network developer. Please try to reproduce >>> the same thing on a newer kernel release and see if the result is the >>> same or not. If you can find a change that I missed, please let me know >>> and I will be glad to apply it. >> >> maowenan, there were five patches in the original upstream set to >> address SegmentSmack: >> >> tcp: free batches of packets in tcp_prune_ofo_queue() >> tcp: avoid collapses in tcp_prune_queue() if possible >> tcp: detect malicious patterns in tcp_collapse_ofo_queue() >> t >> cp: call tcp_drop() from tcp_data_queue_ofo() >> tcp: add >> tcp_ooo_try_coalesce() helper >> >> I believe that the first one, "free batches of packets..." is not >> needed in 4.4 because we only have a simple queue of packets there >> anyway, so we're dropping everything each time and don't need the >> heuristics for how many to drop. >> >> That leaves two more which have so far not been backported to 4.4; can >> you try applying them and see if it resolves the problem for you? > > I have tried to add below two patches in 4.4 stable, since I can't apply > tcp: add tcp_ooo_try_coalesce() helper because conflicts, it has the same result > after testing, and the cpu usage has not obviously been improved. > > tcp: call tcp_drop() from tcp_data_queue_ofo() > tcp: increment sk_drops for dropped rx packets > > @Eric Dumazet, do you have any comments about this, and shall we apply which patches > to fix in stable branch? I have checked [PATCH net 3/5] tcp: detect malicious patterns in tcp_collapse_ofo_queue(), and found that stable branch 4.4 and 3.18 are tiny different from latest mainline, stable 4.4 branch: range_truesize = skb->truesize; latest mainline code: range_truesize += skb->truesize; I wonder know why there is some difference here, anything I have ignored? thank you. @@ -4923,11 +4925,20 @@ static void tcp_collapse_ofo_queue(struct sock *sk) if (!skb || after(TCP_SKB_CB(skb)->seq, end) || before(TCP_SKB_CB(skb)->end_seq, start)) { - tcp_collapse(sk, NULL, &tp->out_of_order_queue, - head, skb, start, end); + /* Do not attempt collapsing tiny skbs */ + if (range_truesize != head->truesize || + end - start >= SKB_WITH_OVERHEAD(SK_MEM_QUANTUM)) { + tcp_collapse(sk, NULL, &tp->out_of_order_queue, + head, skb, start, end); + } else { + sum_tiny += range_truesize; + if (sum_tiny > sk->sk_rcvbuf >> 3) + return; + } goto new_range; } + range_truesize += skb->truesize; //stable 4.4 is different from mainline. if (unlikely(before(TCP_SKB_CB(skb)->seq, start))) start = TCP_SKB_CB(skb)->seq; if (after(TCP_SKB_CB(skb)->end_seq, end)) > >> >> Thanks. >> > > > . >