From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751070AbaK0P4V (ORCPT ); Thu, 27 Nov 2014 10:56:21 -0500 Received: from aserp1040.oracle.com ([141.146.126.69]:20888 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750816AbaK0P4U (ORCPT ); Thu, 27 Nov 2014 10:56:20 -0500 Date: Thu, 27 Nov 2014 18:57:52 +0300 From: Dan Carpenter To: Steven Rostedt Cc: Ingo Molnar , linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org Subject: [patch v2] tracing: truncated output is better than nothing Message-ID: <20141127155752.GA21914@mwanda> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141126102244.4bffa4b2@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: ucsinet22.oracle.com [156.151.31.94] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The initial reason for this patch is that I noticed that: if (len > TRACE_BUF_SIZE) is off by one. In this code, if len == TRACE_BUF_SIZE, then it means we have truncated the last character off the output string. If we truncate two or more characters then we exit without printing. After some discussion, we decided that printing truncated data is better than not printing at all so we should just use vscnprintf() and remove the test entirely. Also I have updated memcpy() to copy the NUL char instead of setting the NUL in a separate step. Signed-off-by: Dan Carpenter diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 42a822d..ab76b7b 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2160,9 +2160,7 @@ __trace_array_vprintk(struct ring_buffer *buffer, goto out; } - len = vsnprintf(tbuffer, TRACE_BUF_SIZE, fmt, args); - if (len > TRACE_BUF_SIZE) - goto out; + len = vscnprintf(tbuffer, TRACE_BUF_SIZE, fmt, args); local_save_flags(flags); size = sizeof(*entry) + len + 1; @@ -2173,8 +2171,7 @@ __trace_array_vprintk(struct ring_buffer *buffer, entry = ring_buffer_event_data(event); entry->ip = ip; - memcpy(&entry->buf, tbuffer, len); - entry->buf[len] = '\0'; + memcpy(&entry->buf, tbuffer, len + 1); if (!call_filter_check_discard(call, entry, buffer, event)) { __buffer_unlock_commit(buffer, event); ftrace_trace_stack(buffer, flags, 6, pc);