From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752073AbbIESiU (ORCPT ); Sat, 5 Sep 2015 14:38:20 -0400 Received: from mail-yk0-f179.google.com ([209.85.160.179]:35947 "EHLO mail-yk0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751027AbbIESiH (ORCPT ); Sat, 5 Sep 2015 14:38:07 -0400 Date: Sat, 5 Sep 2015 14:38:01 -0400 From: Tejun Heo To: "Richard W.M. Jones" Cc: Josh Boyer , Jeff Moyer , msnitzer@redhat.com, Li Zefan , Johannes Weiner , cgroups@vger.kernel.org, "Linux-Kernel@Vger. Kernel. Org" Subject: Re: __blkg_lookup oops with 4.2-rcX Message-ID: <20150905183801.GA8231@mtj.duckdns.org> References: <20150902145307.GG22326@mtj.duckdns.org> <20150902153255.GH22326@mtj.duckdns.org> <20150904104602.GN29283@redhat.com> <20150904171302.GE25329@mtj.duckdns.org> <20150904204244.GQ29283@redhat.com> <20150905153439.GA18461@redhat.com> <20150905154840.GA19460@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150905154840.GA19460@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Sep 05, 2015 at 04:48:40PM +0100, Richard W.M. Jones wrote: > On Sat, Sep 05, 2015 at 04:34:39PM +0100, Richard W.M. Jones wrote: > > [ 52.259269] BUG: unable to handle kernel NULL pointer dereference at 00000000000009c8 > > [ 52.259269] IP: [] __blkg_lookup+0x40/0xe0 > > And also: > > $ addr2line -e /usr/lib/debug/lib/modules/4.3.0-0.rc0.git7.1.rwmj3.fc24.x86_64/vmlinux ffffffff813f8b10 > /usr/src/debug/kernel-4.2.fc24/linux-4.3.0-0.rc0.git7.1.rwmj3.fc24.x86_64/block/blk-cgroup.c:158 > > 152 /* > 153 * Hint didn't match. Look up from the radix tree. Note that the > 154 * hint can only be updated under queue_lock as otherwise @blkg > 155 * could have already been removed from blkg_tree. The caller is > 156 * responsible for grabbing queue_lock if @update_hint. > 157 */ > 158 blkg = radix_tree_lookup(&blkcg->blkg_tree, q->id); Okay, found the bug. It was an existing problem which got exposed by the recent bypass change. Will soon post a patch. Thanks a lot! -- tejun