From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [RFC PATCH] fix select(2) race between main_loop_wait and qemu_aio_wait Date: Mon, 05 Mar 2012 16:24:10 +0200 Message-ID: <4F54CC8A.5010509@redhat.com> References: <1330936455-23802-1-git-send-email-pbonzini@redhat.com> <4F548263.1070905@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Cc: Paolo Bonzini , qemu-devel@nongnu.org, kvm@vger.kernel.org, laurent@vivier.eu, anthony@codemonkey.ws To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:62161 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932581Ab2CEOYS (ORCPT ); Mon, 5 Mar 2012 09:24:18 -0500 In-Reply-To: <4F548263.1070905@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: On 03/05/2012 11:07 AM, Jan Kiszka wrote: > On 2012-03-05 09:34, Paolo Bonzini wrote: > > This is quite ugly. Two threads, one running main_loop_wait and > > one running qemu_aio_wait, can race with each other on running the > > same iohandler. The result is that an iohandler could run while the > > underlying socket is not readable or writable, with possibly ill effects. > > Hmm, isn't it a problem already that a socket is polled by two threads > at the same time? Can't that be avoided? Could it be done simply by adding a mutex there? It's hardly a clean fix, but it's not a clean problem. > Long-term, I'd like to cut out certain file descriptors from the main > loop and process them completely in separate threads (for separate > locking, prioritization etc.). Dunno how NBD works, but maybe it should > be reworked like this already. Ideally qemu_set_fd_handler2() should be made thread local, and each device thread would run a copy of the main loop, just working on different data. -- error compiling committee.c: too many arguments to function