Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935545AbaDJOqx (ORCPT ); Thu, 10 Apr 2014 10:46:53 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39427 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933057AbaDJOqv (ORCPT ); Thu, 10 Apr 2014 10:46:51 -0400 Date: Thu, 10 Apr 2014 16:46:55 +0200 From: Oleg Nesterov To: Steven Rostedt Cc: Mathieu Desnoyers , Frederic Weisbecker , LKML , Andrew Morton , Ingo Molnar Subject: Re: [PATCH RESEND 2/2] tracing: syscall_regfunc() should not skip kernel threads Message-ID: <20140410144655.GA25316@redhat.com> References: <1397059882-23063-1-git-send-email-fweisbec@gmail.com> <1397059882-23063-3-git-send-email-fweisbec@gmail.com> <360091921.1294.1397060915052.JavaMail.zimbra@efficios.com> <20140409124249.4081e665@gandalf.local.home> <20140409170505.GA27638@redhat.com> <20140409170616.GC27638@redhat.com> <20140410092842.1f9a8760@gandalf.local.home> <20140410133855.GC12228@redhat.com> <20140410102816.24337ffe@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140410102816.24337ffe@gandalf.local.home> 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 04/10, Steven Rostedt wrote: > > On Thu, 10 Apr 2014 15:38:55 +0200 > Oleg Nesterov wrote: > > > > > However, this means that a user-space task spawned by > > > > call_usermodehelper() won't report the system calls if > > > > kernel_execve() is called when sys_tracepoint_refcount != 0. > > > > > > What about doing the set there? That is, we could add a check in the > > > call_userspacehelper() just before it does the do_execve, that if > > > sys_tracepoint_refcount is set, we set the TIF flag. > > > > But for what? > > Isn't call_usermodehelper() the reason you added this? Sure. I meant, why complicate ____call_usermodehelper() and keep the unnecessary complication (PF_KTHREAD check( in syscall_*regfunc() ? > > And if we do this, ____call_usermodehelper() needs write_lock_irq(tasklist) > > to serialize with syscall_*regfunc(). > > You mean for the slight race between checking if its set and when the > tracepoint is actually activated? Or deactivated. > I don't think we really care about that race. OK, I won't argue. I agree, the problem is minor, but in this case imho it is better to do nothing than add the racy fix. > I mean, the tracepoint is > activated usually by humans, and if they enabled it just as a usermode > helper is activated, and those are really fast to run, do we even care > if it is missed? A user space task spawned by call_usermodehelper() can do everything, it can run forever. > Now, if tracing is on and we need to set the flag, that should take the > task list lock to make sure that we don't miss clearing it. Missing the > set isn't a big deal, but missing the clearing of the flag is. > > void tracepoint_check_syscalls(void) > { > if (!sys_tracepoint_refcount) > return; > > read_lock(&tasklist_lock); > /* Make sure it wasn't cleared since taking the lock */ > if (sys_tracepoint_refcount) > set_tsk_thread_flag(current, TIF_SYSCALL_TRACEPOINT); > read_unlock(&tasklist_lock); > } And how this can help to avoid the race? We need write_lock_irq(). Perhaps I missed something... and I simply do not understand why do you want to do this. Oleg. -- 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/