From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 38288C2D0DC for ; Thu, 2 Jan 2020 13:28:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0389D20863 for ; Thu, 2 Jan 2020 13:28:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728409AbgABN2v (ORCPT ); Thu, 2 Jan 2020 08:28:51 -0500 Received: from s3.sipsolutions.net ([144.76.43.62]:57490 "EHLO sipsolutions.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728323AbgABN2u (ORCPT ); Thu, 2 Jan 2020 08:28:50 -0500 Received: by sipsolutions.net with esmtpsa (TLS1.3:ECDHE_SECP256R1__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.92.3) (envelope-from ) id 1in0Wl-005R8Q-C2; Thu, 02 Jan 2020 14:28:39 +0100 Message-ID: <1762437703fd150bb535ee488c78c830f107a531.camel@sipsolutions.net> Subject: Re: PROBLEM: Wireless networking goes down on Acer C720P Chromebook (bisected) From: Johannes Berg To: Stephen Oberholtzer , toke@redhat.com Cc: "David S. Miller" , linux-wireless@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Date: Thu, 02 Jan 2020 14:28:35 +0100 In-Reply-To: (sfid-20200101_015805_066597_5A8428D1) References: (sfid-20200101_015805_066597_5A8428D1) Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.34.2 (3.34.2-1.fc31) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2019-12-31 at 19:49 -0500, Stephen Oberholtzer wrote: > Wireless networking goes down on Acer C720P Chromebook (bisected) > > Culprit: 7a89233a ("mac80211: Use Airtime-based Queue Limits (AQL) on > packet dequeue") > > I found that the newest kernel (5.4) displayed a curious issue on my > Acer C720P Chromebook: shortly after bringing networking up, all > connections would suddenly fail. I discovered that I could > consistently reproduce the issue by ssh'ing into the machine and > running 'dmesg' -- on a non-working kernel; I would get partial > output, and then the connection would completely hang. This was so > consistent, in fact, that I was able to leverage it to automate the > process from 'git bisect run'. > > KEYWORDS: c720p, chromebook, wireless, networking, mac80211 > > KERNEL: any kernel containing commit 7a89233a ("mac80211: Use > Airtime-based Queue Limits (AQL) on packet dequeue") > > I find this bit in the offending commit's message suspicious: > > > This patch does *not* include any mechanism to wake a throttled TXQ again, > > on the assumption that this will happen anyway as a side effect of whatever > > freed the skb (most commonly a TX completion). > > Methinks this assumption is not a fully valid one. I think I found at least one hole in this, but IIRC (it was before my vacation, sorry) it was pretty unlikely to actually happen. Perhaps there are more though. https://lore.kernel.org/r/b14519e81b6d2335bd0cb7dcf074f0d1a4eec707.camel@sipsolutions.net > I'll be happy to test any patches. If you need some printk calls, just > tell me where to put 'em. Do you get any output at all? Like a WARN_ON() for an underflow, or something? johannes