From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [RFC PATCH v2] Add rcu user eqs exception hooks for async page fault Date: Wed, 28 Nov 2012 15:53:45 +0200 Message-ID: <20121128135345.GG928@redhat.com> References: <1353993325.14050.49.camel@ThinkPad-T5421.cn.ibm.com> <1354090704.3054.13.camel@ThinkPad-T5421.cn.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mx1.redhat.com ([209.132.183.28]:56578 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932175Ab2K1Nxx (ORCPT ); Wed, 28 Nov 2012 08:53:53 -0500 Content-Disposition: inline In-Reply-To: Sender: linux-next-owner@vger.kernel.org List-ID: To: Frederic Weisbecker Cc: Li Zhong , linux-next list , LKML , paulmck@linux.vnet.ibm.com, sasha.levin@oracle.com, avi@redhat.com On Wed, Nov 28, 2012 at 01:55:42PM +0100, Frederic Weisbecker wrote: > > So I still want to remove it. And later if it shows that we really needs > > rcu somewhere in this code path, maybe we could use RCU_NONIDLE() to > > protect it. ( The suspicious RCU usage reported in commit > > c5e015d4949aa665 seems related to schedule(), which is not in the code > > path if we are in cpu idle eqs ) > > Yes but if rcu_irq_*() calls are fine to be called there, and I > believe they are because exception_enter() exits the user mode, we > should start to protect there right now instead of waiting for a > potential future warning of illegal RCU use. > Async page not present is not much different from regular page fault exception when it happens not on idle task (regular #PF cannot happen on idle task), but code have a special handling for idle task. So why do you think rcu_irq_*() is required here, but not in page fault handler? > > > > I think we still need Gleb's patch about the idle check in > > kvm_async_pf_task_wait(), and maybe another patch for the > > exit_idle()/enter_idle() issue. > > Right. > Done. -- Gleb.