Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751399AbaDUODT (ORCPT ); Mon, 21 Apr 2014 10:03:19 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:42501 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751136AbaDUODR (ORCPT ); Mon, 21 Apr 2014 10:03:17 -0400 Date: Mon, 21 Apr 2014 10:03:16 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Oliver Neukum cc: linux-kernel@vger.kernel.org Subject: Re: question on read_barrier_depends In-Reply-To: <1398073259.9256.3.camel@linux-fkkt.site> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 21 Apr 2014, Oliver Neukum wrote: > > In addition, the following code in kfifo_get() does this: > > > > *(typeof(__tmp->type))__val = \ > > (__is_kfifo_ptr(__tmp) ? \ > > ((typeof(__tmp->type))__kfifo->data) : \ > > (__tmp->buf) \ > > )[__kfifo->out & __tmp->kfifo.mask]; \ > > smp_wmb(); \ > > __kfifo->out++; \ > > > > It looks like the smp_wmb() should really be smp_mb(), because it > > separates the _read_ for val from the _write_ of kfifo->out. > > On the third hand, I now think wmb() is sufficient, because > there's also a write to __val. It does depend on the read > of buf[out & mask], but if no CPU does speculative writes > it must be correct. You are right; I missed that. Good point. Alan Stern -- 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/