Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756522Ab2K0QvP (ORCPT ); Tue, 27 Nov 2012 11:51:15 -0500 Received: from mail-yh0-f46.google.com ([209.85.213.46]:39779 "EHLO mail-yh0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756117Ab2K0QvN (ORCPT ); Tue, 27 Nov 2012 11:51:13 -0500 MIME-Version: 1.0 In-Reply-To: <20121127163910.GL12969@redhat.com> References: <1353993325.14050.49.camel@ThinkPad-T5421.cn.ibm.com> <20121127154455.GK12969@redhat.com> <20121127163910.GL12969@redhat.com> Date: Tue, 27 Nov 2012 17:51:12 +0100 Message-ID: Subject: Re: [RFC PATCH] Fix abnormal rcu dynticks_nesting values related to async page fault From: Frederic Weisbecker To: Gleb Natapov Cc: Li Zhong , linux-next list , LKML , paulmck@linux.vnet.ibm.com, sasha.levin@oracle.com, avi@redhat.com Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1230 Lines: 26 2012/11/27 Gleb Natapov : > On Tue, Nov 27, 2012 at 04:56:30PM +0100, Frederic Weisbecker wrote: >> 2012/11/27 Gleb Natapov : >> > For KVM_PV_REASON_PAGE_NOT_PRESENT it behaves like an exception. >> >> Ok. >> There seem to be a bug in kvm_async_pf_task_wait(). Using >> idle_cpu(cpu) to find out if the current task is the idle task may not >> work if there is pending wake up. Me may schedule another task but >> when that other task sleeps later we can't schedule back to idle until >> the fault is completed. >> >> The right way is to use is_idle_task(current) > But if there is pending wake up then scheduling to the waked up task is > exactly what we want. Ok, but what if that task goes to sleep soon after beeing scheduled and there is no other task on the runqueue and the page fault has not been handled yet? The only thing you can do is to schedule the idle task. But the idle task is waiting for the fault completion so you can't do that. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/