From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=33856 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PjruZ-0004nr-BS for qemu-devel@nongnu.org; Mon, 31 Jan 2011 06:27:12 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PjruY-0002WY-8l for qemu-devel@nongnu.org; Mon, 31 Jan 2011 06:27:11 -0500 Received: from thoth.sbs.de ([192.35.17.2]:21564) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PjruX-0002W4-SW for qemu-devel@nongnu.org; Mon, 31 Jan 2011 06:27:10 -0500 Message-ID: <4D469C87.3080909@siemens.com> Date: Mon, 31 Jan 2011 12:27:03 +0100 From: Jan Kiszka MIME-Version: 1.0 References: <4D417F1F.7020302@siemens.com> <4D418230.1010801@siemens.com> <4D4688EB.30408@redhat.com> In-Reply-To: <4D4688EB.30408@redhat.com> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] Re: [PATCH v3 14/22] kvm: Fix race between timer signals and vcpu entry under !IOTHREAD List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity Cc: Marcelo Tosatti , "qemu-devel@nongnu.org" , "kvm@vger.kernel.org" , Stefan Hajnoczi On 2011-01-31 11:03, Avi Kivity wrote: > On 01/27/2011 04:33 PM, Jan Kiszka wrote: >> Found by Stefan Hajnoczi: There is a race in kvm_cpu_exec between >> checking for exit_request on vcpu entry and timer signals arriving >> before KVM starts to catch them. Plug it by blocking both timer related >> signals also on !CONFIG_IOTHREAD and process those via signalfd. >> >> As this fix depends on real signalfd support (otherwise the timer >> signals only kick the compat helper thread, and the main thread hangs), >> we need to detect the invalid constellation and abort configure. >> >> Signed-off-by: Jan Kiszka >> CC: Stefan Hajnoczi >> --- >> >> I don't want to invest that much into !IOTHREAD anymore, so let's see if >> the proposed catch&abort is acceptable. >> > > I don't understand the dependency on signalfd. The normal way of doing > things, either waiting for the signal in sigtimedwait() or in > ioctl(KVM_RUN), works with SIGALRM just fine. And how would you be kicked out of the select() call if it is waiting with a timeout? We only have a single thread here. The only alternative is Stefan's original proposal. But that required fiddling with the signal mask twice per KVM_RUN. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux