From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH] sched: access local runqueue directly in single_task_running Date: Fri, 18 Sep 2015 13:35:39 +0200 Message-ID: <20150918113539.GL3604@twins.programming.kicks-ass.net> References: <1442568465-71559-1-git-send-email-dingel@linux.vnet.ibm.com> <55FBF4FD.6060609@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Dominik Dingel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Ingo Molnar , Tim Chen , stable@vger.kernel.org To: Paolo Bonzini Return-path: Content-Disposition: inline In-Reply-To: <55FBF4FD.6060609@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Fri, Sep 18, 2015 at 01:26:53PM +0200, Paolo Bonzini wrote: > > +++ b/kernel/sched/core.c > > @@ -2614,13 +2614,13 @@ unsigned long nr_running(void) > > > > /* > > * Check if only the current task is running on the cpu. > > + * > > + * Caution result is subject to time-of-check-to-time-of-use race, > > + * every caller is responsible to set up additional fences if necessary. > > Let's expand it a bit more: > > * Caution: this function does not check that the caller has disabled > * preemption, thus the result might have a time-of-check-to-time-of-use > * race. The caller is responsible to use this correctly, for example: > * > * - use it from a non-preemptable section > * > * - use it from a thread that is bound to a single CPU > * > * - use it in a loop where each iteration takes very little time > * (e.g. a polling loop) > */ > > I'll include it in my pull request. In which case: Acked-by: Peter Zijlstra (Intel)