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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 96D44C433E3 for ; Mon, 3 Aug 2020 04:15:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 76C5B20775 for ; Mon, 3 Aug 2020 04:15:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="s0z2n5m6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725268AbgHCEPx (ORCPT ); Mon, 3 Aug 2020 00:15:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51438 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725924AbgHCEPt (ORCPT ); Mon, 3 Aug 2020 00:15:49 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5D4FBC06174A for ; Sun, 2 Aug 2020 21:15:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=wYTRpjfymCgNRLej5wa/gQSa8PBvdtAZGCPIUw1orIo=; b=s0z2n5m6s1IMkI7HeCbgC2dlPf yOPQ7BAYBx8xmZVunwFYfWN6nYPt2x1KIyS4lLLOgdNFTKvWGE3D6Hz8Fs7CFfPz7MZrU7FKpf+He 0f2MnechNqzWqFvqwXebGadiknhHgLO+GyC+wC8MWnmPga/96miDjjZ0BjO6cxzUYfOgpyTeGCUqD ZWCjR3OtOz+GGYf6k0OVKpl6w1WFCRDWFRU/T8VyyWFTeI0nqLzVyKMPJ0Gh7b8eFxen2dVvGmtyd CD/MeQ1G2iuvQRH+x/whh1+kZv4JCaWg4G/iUrADUtJvDi+dkKHTLzkq7kGreM6LnKrt2arjVrndp k/WWaalA==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1k2Rt5-0006Ub-5j; Mon, 03 Aug 2020 04:15:47 +0000 Date: Mon, 3 Aug 2020 05:15:47 +0100 From: Matthew Wilcox To: David Niklas Cc: linux-doc@vger.kernel.org, corbet@lwn.net Subject: Re: PROBLEM: Missing debug instructions when EIP is not present Message-ID: <20200803041547.GZ23808@casper.infradead.org> References: <20200802224652.6be413fe@Phenom-II-x6.niklas.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200802224652.6be413fe@Phenom-II-x6.niklas.com> Sender: linux-doc-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Sun, Aug 02, 2020 at 10:46:52PM -0400, David Niklas wrote: > The file: Documentation/admin-guide/bug-hunting.rst > gives instructions on how to find the offending line of code using EIP. > My particular bug that I need to report doesn't have EIP listed -- at > least not by name. I tried to guess what EIP was in > my case "__schedule+0x29e/0x6c0" but that didn't produce any results in > gdb on my debug kernel. EIP is the x86-32 name for what x86-64 calls RIP. Not much help in this case, because it's pointing to a userspace address (actually, I think it's the vdso). > I don't appear to have the referenced module type problem: > "[] :jbd:log_wait_commit+0xa3/0xf5" > > I'm totally new to kernel debugging so the documentation is really > important and I'm rather frustrated in even bothering to read it as it's > incomplete/unhelpful. > > Here's the exact bug I'm trying to tackle. > > [68812.480447] INFO: task CacheThread_Blo:9414 blocked for more than 480 > seconds. That's the important bit. Your task tried to take a mutex and 480 seconds later, it still didn't have it. > [68812.480459] Not tainted 4.14.184-nopreempt-AMDGPU-dav9 > #1 [68812.480464] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" > disables this message. [68812.480469] CacheThread_Blo D 0 9414 9082 > 0x00000080 [68812.480476] Call Trace: > [68812.480494] __schedule+0x29e/0x6c0 > [68812.480505] schedule+0x32/0x80 > [68812.480513] schedule_preempt_disabled+0xa/0x10 > [68812.480520] __mutex_lock.isra.1+0x26b/0x4e0 > [68812.480550] ? do_journal_begin_r+0xbe/0x390 [reiserfs] > [68812.480570] do_journal_begin_r+0xbe/0x390 [reiserfs] The mutex it tried to take was in the function do_journal_begin_r(). Best of luck debugging reiserfs problems these days. It doesn't get a lot of love.