Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753764AbYGMA22 (ORCPT ); Sat, 12 Jul 2008 20:28:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751803AbYGMA2R (ORCPT ); Sat, 12 Jul 2008 20:28:17 -0400 Received: from OSB1387.piap.pl ([195.187.100.11]:41640 "EHLO khc.piap.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751616AbYGMA2Q (ORCPT ); Sat, 12 Jul 2008 20:28:16 -0400 To: , netdev@vger.kernel.org Subject: [bisected] kernel panic 2.6.22 -> 2.6.26-rc9+ From: Krzysztof Halasa Date: Sun, 13 Jul 2008 02:28:13 +0200 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4111 Lines: 121 Hi, Bisected the panic. It seems it occurs on my ARM IXP4xx big-endian system with USB ADSL PPP over ATM connection (Thomson/Alcatel Speedtouch). It doesn't seem to occur on the same IXP4xx with Ethernet or V.35 WAN, and it doesn't occur on i386 + the same Speedtouch ADSL. The kernel is basically unpatched, the only extra patch applied is the platform support (nothing magic). Generally to trigger the panic one has to request a TCP data stream over that PPPoATM connection. Reverting the commit on top of 2.6.25.10 fixes the problem. Now what's wrong with that? 7e58886b45bc4a309aeaa8178ef89ff767daaf7f: author Stephen Hemminger [TCP]: cubic optimization Use willy's work in optimizing cube root by having table for small values. --- a/net/ipv4/tcp_cubic.c +++ b/net/ipv4/tcp_cubic.c @@ -91,23 +91,51 @@ static void bictcp_init(struct sock *sk) tcp_sk(sk)->snd_ssthresh = initial_ssthresh; } -/* - * calculate the cubic root of x using Newton-Raphson +/* calculate the cubic root of x using a table lookup followed by one + * Newton-Raphson iteration. + * Avg err ~= 0.195% */ static u32 cubic_root(u64 a) { - u32 x; - - /* Initial estimate is based on: - * cbrt(x) = exp(log(x) / 3) + u32 x, b, shift; + /* + * cbrt(x) MSB values for x MSB values in [0..63]. + * Precomputed then refined by hand - Willy Tarreau + * + * For x in [0..63], + * v = cbrt(x << 18) - 1 + * cbrt(x) = (v[x] + 10) >> 6 */ - x = 1u << (fls64(a)/3); + static const u8 v[] = { + /* 0x00 */ 0, 54, 54, 54, 118, 118, 118, 118, + /* 0x08 */ 123, 129, 134, 138, 143, 147, 151, 156, + /* 0x10 */ 157, 161, 164, 168, 170, 173, 176, 179, + /* 0x18 */ 181, 185, 187, 190, 192, 194, 197, 199, + /* 0x20 */ 200, 202, 204, 206, 209, 211, 213, 215, + /* 0x28 */ 217, 219, 221, 222, 224, 225, 227, 229, + /* 0x30 */ 231, 232, 234, 236, 237, 239, 240, 242, + /* 0x38 */ 244, 245, 246, 248, 250, 251, 252, 254, + }; + + b = fls64(a); + if (b < 7) { + /* a in [0..63] */ + return ((u32)v[(u32)a] + 35) >> 6; + } + + b = ((b * 84) >> 8) - 1; + shift = (a >> (b * 3)); - /* converges to 32 bits in 3 iterations */ - x = (2 * x + (u32)div64_64(a, (u64)x*(u64)x)) / 3; - x = (2 * x + (u32)div64_64(a, (u64)x*(u64)x)) / 3; - x = (2 * x + (u32)div64_64(a, (u64)x*(u64)x)) / 3; + x = ((u32)(((u32)v[shift] + 10) << b)) >> 6; + /* + * Newton-Raphson iteration + * 2 + * x = ( 2 * x + a / x ) / 3 + * k+1 k k + */ + x = (2 * x + (u32)div64_64(a, (u64)x * (u64)(x - 1))); + x = ((x * 341) >> 10); return x; } PC is at bictcp_cong_avoid+0x33c/0x454 Backtrace: bictcp_cong_avoid+0x0/0x454 from tcp_cong_avoid+0x1c/0x30 tcp_cong_avoid+0x0/0x30 from tcp_ack+0x156c/0x1c6c r4:00000000 tcp_ack+0x0/0x1c6c from tcp_rcv_established+0x4a8/0x76c tcp_rcv_established+0x0/0x76c from tcp_v4_do_rcv+0x25c/0x458 tcp_v4_do_rcv+0x0/0x458 from tcp_v4_rcv+0x6c4/0x7ec tcp_v4_rcv+0x0/0x7ec from ip_local_deliver_finish+0xe4/0x24c ip_local_deliver_finish+0x0/0x24c from ip_local_deliver+0x4c/0xac r7:c043817c r6:c6818612 r5:c6a6a3c0 r4:c6a6a3c0 ip_local_deliver+0x0/0xac from ip_rcv_finish+0x114/0x378 r4:80000000 ip_rcv_finish+0x0/0x378 from ip_rcv+0x1f8/0x2a8 ip_rcv+0x0/0x2a8 from netif_receive_skb+0x36c/0x4a4 r7:00000800 r6:c0405e80 r5:c6a6a3c0 r4:c0436d54 netif_receive_skb+0x0/0x4a4 from process_backlog+0x88/0x14c r8:00000040 r7:c0436d24 r6:00000000 r5:c0436d0c r4:c6912c00 process_backlog+0x0/0x14c from net_rx_action+0xb4/0x1c4 net_rx_action+0x0/0x1c4 from __do_softirq+0x68/0xe0 _do_softirq+0x0/0xe0 from irq_exit+0x48/0x50 r7:00000000 r6:c04344d0 r5:c040ae24 r4:00000014 irq_exit+0x0/0x50 from asm_do_IRQ+0x48/0x5c asm_do_IRQ+0x0/0x5c from __irq_svc+0x24/0x60 ... -- Krzysztof Halasa -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/