From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: Endless loop in qcow2_alloc_cluster_offset Date: Mon, 07 Dec 2009 16:25:46 +0100 Message-ID: <4B1D1E7A.8060307@siemens.com> References: <4B0537EB.4000909@siemens.com> <4B055AEF.4030406@redhat.com> <4B055D32.3040601@siemens.com> <4B1D0E34.6070907@siemens.com> <4B1D1618.2080900@siemens.com> <4B1D1946.7080908@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Cc: qemu-devel , kvm To: Kevin Wolf Return-path: Received: from thoth.sbs.de ([192.35.17.2]:23135 "EHLO thoth.sbs.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935216AbZLGP0B (ORCPT ); Mon, 7 Dec 2009 10:26:01 -0500 In-Reply-To: <4B1D1946.7080908@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Kevin Wolf wrote: > Am 07.12.2009 15:50, schrieb Jan Kiszka: >> Jan Kiszka wrote: >>> And now it happened again (qemu-kvm head, during kernel installation >>> from network onto local qcow2-disk). Any clever idea how to proceed with >>> this? >>> >>> I could try to run the step in a loop, hopefully retriggering it once in >>> a (likely longer) while. But then we need some good instrumentation first. >>> >> Maybe I'm seeing ghosts, and I don't even have a minimal clue about what >> goes on in the code, but this looks fishy: >> >> preallocate() invokes qcow2_alloc_cluster_offset() passing &meta, a >> stack variable. It seems that qcow2_alloc_cluster_offset() may insert >> this structure into cluster_allocs and leave it there. So we corrupt the >> queue as soon as preallocate() returns, no? > > preallocate() is about metadata preallocation during image creation. It > is only ever run by qemu-img. Apart from that it calls > run_dependent_requests() which removes the request from the list again. OK, I see - was far too easy anyway. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1NHfTI-0007V7-Ea for qemu-devel@nongnu.org; Mon, 07 Dec 2009 10:25:56 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1NHfTC-0007O8-EM for qemu-devel@nongnu.org; Mon, 07 Dec 2009 10:25:55 -0500 Received: from [199.232.76.173] (port=40225 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1NHfTC-0007Np-71 for qemu-devel@nongnu.org; Mon, 07 Dec 2009 10:25:50 -0500 Received: from thoth.sbs.de ([192.35.17.2]:23041) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1NHfTC-0001Xo-3Q for qemu-devel@nongnu.org; Mon, 07 Dec 2009 10:25:50 -0500 Message-ID: <4B1D1E7A.8060307@siemens.com> Date: Mon, 07 Dec 2009 16:25:46 +0100 From: Jan Kiszka MIME-Version: 1.0 References: <4B0537EB.4000909@siemens.com> <4B055AEF.4030406@redhat.com> <4B055D32.3040601@siemens.com> <4B1D0E34.6070907@siemens.com> <4B1D1618.2080900@siemens.com> <4B1D1946.7080908@redhat.com> In-Reply-To: <4B1D1946.7080908@redhat.com> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] Re: Endless loop in qcow2_alloc_cluster_offset List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: qemu-devel , kvm Kevin Wolf wrote: > Am 07.12.2009 15:50, schrieb Jan Kiszka: >> Jan Kiszka wrote: >>> And now it happened again (qemu-kvm head, during kernel installation >>> from network onto local qcow2-disk). Any clever idea how to proceed with >>> this? >>> >>> I could try to run the step in a loop, hopefully retriggering it once in >>> a (likely longer) while. But then we need some good instrumentation first. >>> >> Maybe I'm seeing ghosts, and I don't even have a minimal clue about what >> goes on in the code, but this looks fishy: >> >> preallocate() invokes qcow2_alloc_cluster_offset() passing &meta, a >> stack variable. It seems that qcow2_alloc_cluster_offset() may insert >> this structure into cluster_allocs and leave it there. So we corrupt the >> queue as soon as preallocate() returns, no? > > preallocate() is about metadata preallocation during image creation. It > is only ever run by qemu-img. Apart from that it calls > run_dependent_requests() which removes the request from the list again. OK, I see - was far too easy anyway. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux