From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753209AbaKZOnK (ORCPT ); Wed, 26 Nov 2014 09:43:10 -0500 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.231]:29923 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750991AbaKZOnI (ORCPT ); Wed, 26 Nov 2014 09:43:08 -0500 Date: Wed, 26 Nov 2014 09:43:06 -0500 From: Steven Rostedt To: Dan Carpenter Cc: Ingo Molnar , linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org Subject: Re: [patch] tracing: off by one in __trace_array_vprintk() Message-ID: <20141126094306.4f465616@gandalf.local.home> In-Reply-To: <20141126143719.GT4893@mwanda> References: <20141126140621.GA18740@mwanda> <20141126092706.5d4038d4@gandalf.local.home> <20141126143719.GT4893@mwanda> X-Mailer: Claws Mail 3.10.1 (GTK+ 2.24.25; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-RR-Connecting-IP: 107.14.168.142:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 26 Nov 2014 17:37:19 +0300 Dan Carpenter wrote: > On Wed, Nov 26, 2014 at 09:27:06AM -0500, Steven Rostedt wrote: > > On Wed, 26 Nov 2014 17:06:21 +0300 > > Dan Carpenter wrote: > > > > > This check says "goto out;" if we had to truncate the string. > > > > > > The "tbuffer" buffer has TRACE_BUF_SIZE bytes. The vsnprintf() function > > > returns the number of characters (not counting the NUL char) which would > > > have been printed if there were space. If we we tried to print > > > TRACE_BUF_SIZE characters, the last character would have been truncated > > > to make space for the NUL character so we should "goto out;". > > > > > > > Oh, and the NUL character is never copied. We copy the string into the > > buffer with: > > > > memcpy(&entry->buf, tbuffer, len); > > > > Where len does not include NUL, and why we add it ourselves. > > Yeah. I noticed that. Probably we should change the memcpy() to: > > memcpy(&entry->buf, tbuffer, len + 1); > > and remove separate NUL assignment? It's a speedup! I'll do it in v2. > I highly doubt it's much of a speed up. And we do that by sacrificing that one byte of buffer, which would lose the printk if len does equal TRACE_BUF_SIZE. I don't see a bug here. What exactly are you trying to fix? -- Steve