From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754938AbZHYQC3 (ORCPT ); Tue, 25 Aug 2009 12:02:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754701AbZHYQC3 (ORCPT ); Tue, 25 Aug 2009 12:02:29 -0400 Received: from mtagate6.de.ibm.com ([195.212.17.166]:60476 "EHLO mtagate6.de.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754680AbZHYQC2 (ORCPT ); Tue, 25 Aug 2009 12:02:28 -0400 Date: Tue, 25 Aug 2009 18:02:37 +0200 From: Hendrik Brueckner To: Frederic Weisbecker Cc: Hendrik Brueckner , Jason Baron , linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, rostedt@goodmis.org, peterz@infradead.org, mathieu.desnoyers@polymtl.ca, jiayingz@google.com, mbligh@google.com, lizf@cn.fujitsu.com, Heiko Carstens , Martin Schwidefsky Subject: Re: [PATCH 08/12] add trace events for each syscall entry/exit Message-ID: <20090825160237.GG4639@cetus.boeblingen.de.ibm.com> Mail-Followup-To: Hendrik Brueckner , Frederic Weisbecker , Jason Baron , linux-kernel@vger.kernel.org, mingo@elte.hu, laijs@cn.fujitsu.com, rostedt@goodmis.org, peterz@infradead.org, mathieu.desnoyers@polymtl.ca, jiayingz@google.com, mbligh@google.com, lizf@cn.fujitsu.com, Heiko Carstens , Martin Schwidefsky References: <20090825141547.GE6114@nowhere> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090825141547.GE6114@nowhere> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 25, 2009 at 04:15:49PM +0200, Frederic Weisbecker wrote: > On Tue, Aug 25, 2009 at 02:50:27PM +0200, Hendrik Brueckner wrote: > > There are at least two scenarios where syscall_get_nr() can return -1: > > > > 1. For example, ptrace stores an invalid syscall number, and thus, > > tracing code resets it. > > (see do_syscall_trace_enter in arch/s390/kernel/ptrace.c) > > > > 2. The syscall_regfunc() (kernel/tracepoint.c) sets the TIF_SYSCALL_FTRACE > > (now: TIF_SYSCALL_TRACEPOINT) flag for all threads which includes > > kernel threads. > > However, the ftrace selftest triggers a kernel oops when testing syscall > > trace points: > > - The kernel thread is started as ususal (do_fork()), > > - tracing code sets TIF_SYSCALL_FTRACE, > > - the ret_from_fork() function is triggered and starts > > ftrace_syscall_exit() with an invalid syscall number. > > > > I wonder if there is any way to identify such situation...? For the second case, it might be an option to avoid setting the TIF_SYSCALL_FTRACE flag for kernel threads. Kernel threads have task_struct->mm set to NULL. (Thanks to Heiko for that hint ;-) The idea is then to check the mm field in syscall_regfunc() and set the flag accordingly. However, I think the patch is an optional add-on becase checking the syscall number is still required for case 1). --- kernel/tracepoint.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/kernel/tracepoint.c +++ b/kernel/tracepoint.c @@ -593,7 +593,9 @@ void syscall_regfunc(void) if (!sys_tracepoint_refcount) { read_lock_irqsave(&tasklist_lock, flags); do_each_thread(g, t) { - set_tsk_thread_flag(t, TIF_SYSCALL_FTRACE); + /* Skip kernel threads. */ + if (t->mm) + set_tsk_thread_flag(t, TIF_SYSCALL_FTRACE); } while_each_thread(g, t); read_unlock_irqrestore(&tasklist_lock, flags); }