From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932923AbcHJWJn (ORCPT ); Wed, 10 Aug 2016 18:09:43 -0400 Received: from mail-yw0-f196.google.com ([209.85.161.196]:33751 "EHLO mail-yw0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932392AbcHJWJk (ORCPT ); Wed, 10 Aug 2016 18:09:40 -0400 Date: Wed, 10 Aug 2016 18:09:32 -0400 From: Tejun Heo To: Roman Pen Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/1] percpu-refcount: do not forget to rcu_barrier() just before freeing Message-ID: <20160810220932.GA2695@mtj.duckdns.org> References: <20160810195539.6588-1-roman.penyaev@profitbricks.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160810195539.6588-1-roman.penyaev@profitbricks.com> User-Agent: Mutt/1.6.2 (2016-07-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 10, 2016 at 09:55:39PM +0200, Roman Pen wrote: > percpu issues some RCU callbacks to synchronize its state, so before > freeing we have to wait all those callbacks to finish. > > E.g. the following simple sequence on stack causes nasty crash: > > struct percpu_ref ref; > > percpu_ref_init(&ref, release, 0, GFP_KERNEL); > percpu_ref_kill(&ref); > percpu_ref_exit(&ref); Hmmm... that's just an illegal sequence of operations. You can't exit a ref which hasn't completed killing yet (the kill callback hasn't been called). Thanks. -- tejun