Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756410AbZFSGoP (ORCPT ); Fri, 19 Jun 2009 02:44:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751615AbZFSGoA (ORCPT ); Fri, 19 Jun 2009 02:44:00 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:53658 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751330AbZFSGn7 (ORCPT ); Fri, 19 Jun 2009 02:43:59 -0400 Message-ID: <4A3B3415.5060304@cn.fujitsu.com> Date: Fri, 19 Jun 2009 14:45:41 +0800 From: Li Zefan User-Agent: Thunderbird 2.0.0.9 (X11/20071115) MIME-Version: 1.0 To: Steven Rostedt CC: Ingo Molnar , Frederic Weisbecker , LKML Subject: [PATCH 1/5] tracing/events: don't increment @pos in s_start() References: <4A3B3372.4040608@cn.fujitsu.com> In-Reply-To: <4A3B3372.4040608@cn.fujitsu.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2304 Lines: 83 While testing syscall tracepoints posted by Jason, I found 3 entries were missing when reading available_events. The output size of available_events is < 4 pages, which means we lost 1 item per page. The cause is, it's wrong to increment @pos in s_start(). Actually there's another bug here -- reading avaiable_events/set_events can race with module unload: # cat available_events | s_start() | s_stop() | | # rmmod foo.ko s_start() | call = list_entry(m->private) | @call might be freed and accessing it will lead to crash. [ Impact fix missing entries when reading available_events/set_events ] Signed-off-by: Li Zefan --- kernel/trace/trace_events.c | 28 ++++++++++++++++++++++------ 1 files changed, 22 insertions(+), 6 deletions(-) diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index aa341ff..4ab596e 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -300,10 +300,18 @@ t_next(struct seq_file *m, void *v, loff_t *pos) static void *t_start(struct seq_file *m, loff_t *pos) { + struct ftrace_event_call *call = NULL; + loff_t l; + mutex_lock(&event_mutex); - if (*pos == 0) - m->private = ftrace_events.next; - return t_next(m, NULL, pos); + + m->private = ftrace_events.next; + for (l = 0; l <= *pos; ) { + call = t_next(m, NULL, &l); + if (!call) + break; + } + return call; } static void * @@ -332,10 +340,18 @@ s_next(struct seq_file *m, void *v, loff_t *pos) static void *s_start(struct seq_file *m, loff_t *pos) { + struct ftrace_event_call *call = NULL; + loff_t l; + mutex_lock(&event_mutex); - if (*pos == 0) - m->private = ftrace_events.next; - return s_next(m, NULL, pos); + + m->private = ftrace_events.next; + for (l = 0; l <= *pos; ) { + call = s_next(m, NULL, &l); + if (!call) + break; + } + return call; } static int t_show(struct seq_file *m, void *v) -- 1.5.4.rc3 -- 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/