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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 8B85BC433F5 for ; Sun, 5 Sep 2021 23:55:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5000260EBA for ; Sun, 5 Sep 2021 23:55:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238428AbhIEX4i (ORCPT ); Sun, 5 Sep 2021 19:56:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33476 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229666AbhIEX4h (ORCPT ); Sun, 5 Sep 2021 19:56:37 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EB83BC061575; Sun, 5 Sep 2021 16:55:33 -0700 (PDT) From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1630886132; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=htNt0m9nOHGLJS+qiDTAK6Mcl3GNSWsAsqlDk5pIWKs=; b=ZJXLgiWpz+VGt31DxlSZe++i8KKC++HF9m4G3FH/T/6A2sCUjWn3aJs+vD53/fjjJqragO ZG8TcI6DvtiZA+MJPz1fTW+ReHyM2H5OdfFVrvG8WCcbI4eNPcP2W8sgQV9VseiZcocov5 /wqMfBAWHQdK3HAlgszTKljhO05jxatal0rNcQE79mUpfJJD4WiEAHOsgDiIV2Qc9HL2Dk 3vnHP9gw8DXZ79EqT4vgitX/80aeSx3qBwmlhxH+65Yh9ipeffGOGR0L0erjz+MJMkt5+m p0CFx36xhtYq8BDb1gCDvGtgkps8o+g3LeL3NOa2bKAsJOAyK22Z9M5ycjmJAg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1630886132; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=htNt0m9nOHGLJS+qiDTAK6Mcl3GNSWsAsqlDk5pIWKs=; b=Tc++YGUfuxCKx0MXvCKWxi6HEsU5Kceo6oXMeNF4ECU00N0iQ8K+JsA6MfvnfrAMQj1FgX Rlj6xebVNdu3hdCg== To: Hillf Danton , syzbot Cc: eric.dumazet@gmail.com, hdanton@sina.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] INFO: task hung in __lru_add_drain_all In-Reply-To: <20210904080739.3026-1-hdanton@sina.com> References: <20210904005650.2914-1-hdanton@sina.com> <20210904080739.3026-1-hdanton@sina.com> Date: Mon, 06 Sep 2021 01:55:31 +0200 Message-ID: <87h7eya87g.ffs@tglx> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Sat, Sep 04 2021 at 16:07, Hillf Danton wrote: > > See if ieee80211_iface_work is burning more CPU cycles than thought, given the > bound workqueue work blocked for more than 143 seconds. > > #syz test git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master > > --- a/net/mac80211/iface.c > +++ b/net/mac80211/iface.c > @@ -1494,6 +1494,7 @@ static void ieee80211_iface_work(struct > > kfree_skb(skb); > kcov_remote_stop(); > + cond_resched(); > } > > /* process status queue */ > @@ -1504,6 +1505,7 @@ static void ieee80211_iface_work(struct > kfree_skb(skb); > > kcov_remote_stop(); > + cond_resched(); > } > > /* then other type-dependent work */ > -- Again. What are you trying to achieve here? ieee80211_iface_work() is a work function invoked from a worker thread in preemptible task context. The kernel config used for this has CONFIG_PREEMPT=y, which means that the context in which you are sprinkling cond_resched() is already fully preemtible and the only reason for this fail would be a fatal bug in the scheduler core or in the preemption mechanism. Pretty unlikely to go unnoticed for anything else than for this particular reproducer. Can you please stop waisting precious compute power? Thanks, tglx