From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH block/for-3.3/core] block: an exiting task should be allowed to create io_context Date: Tue, 3 Jan 2012 09:59:22 -0800 Message-ID: <20120103175922.GC31746@google.com> References: <20111222234639.GS17084@google.com> <20111223004244.GU17084@google.com> <20111225010238.GA6013@htj.dyndns.org> <20111228164836.GP17712@google.com> <20111228211918.GA3516@google.com> <20120103173500.GB31746@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <20120103173500.GB31746@google.com> Sender: linux-next-owner@vger.kernel.org To: Hugh Dickins , Jens Axboe , Shaohua Li Cc: Andrew Morton , Stephen Rothwell , linux-next@vger.kernel.org, LKML , linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org, x86@kernel.org List-Id: linux-scsi@vger.kernel.org Hello, again. Adding Shaohua Li as he fixed a similar issue in 4a0b75c7d0 "block, cfq: fix empty queue crash caused by request merge". The original thread can be read from http://thread.gmane.org/gmane.linux.kernel.next/20064/focus=3D20159 On Tue, Jan 03, 2012 at 09:35:00AM -0800, Tejun Heo wrote: > Happy new year, guys. >=20 > On Wed, Dec 28, 2011 at 01:19:18PM -0800, Tejun Heo wrote: > > > On Wed, Dec 28, 2011 at 9:50 AM, Hugh Dickins = wrote: > > > > "It's the tmpfs swapping test that I've been running, with vari= ations, > > > > for years. =A0System booted with mem=3D700M and 1.5G swap, two = repetitious > > > > make -j20 kernel builds (of a 2.6.24 kernel: I stuck with that = because > > > > the balance of built to unbuilt source grows smaller with later= kernels), > > > > one directly in a tmpfs, the other in a 1k-block ext2 (that I d= rive with > > > > ext4's CONFIG_EXT4_USE_FOR_EXT23) on /dev/loop0 on a 450MB tmpf= s file." > > > > > > > > I doubt much of that (quoted from an older mail to someone else= about > > > > one of the many other bugs it's found) is relevant: maybe just = plenty > > > > of file I/O and swapping. > > >=20 > > > Plain -j4 build isn't triggering anything. I'll try to replicate= the condition. > >=20 > > It's not too reliable but I can reproduce it with -j 22 allmodconfi= g > > build inside qemu w/ 512M of memory. I'll try to find out what's > > going on. >=20 > I misread the code, the problem is empty cfqq on the cfq prio tree. = I > don't think this is caused by recent io_context changes. It looks > like somebody is forgetting to remove cfqq from the dispatch prio tre= e > after emptying a cfqq by removing a request from it. Jens, any ideas= ? That should have been service tree. I couldn't find more missing removals other than the one Shaohua's patch already fixed. Close cooperator selection in cfq_select_queue() seems suspicious tho. I can't see what prevents it from returning an empty coopeator cfqq. I'm trying to verify whether that's the case. Will update when I know more. Thanks. --=20 tejun