Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752151Ab0AZAmL (ORCPT ); Mon, 25 Jan 2010 19:42:11 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752066Ab0AZAmH (ORCPT ); Mon, 25 Jan 2010 19:42:07 -0500 Received: from ey-out-2122.google.com ([74.125.78.25]:18096 "EHLO ey-out-2122.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751621Ab0AZAl7 (ORCPT ); Mon, 25 Jan 2010 19:41:59 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=sybv+7AxFaDy3kcHE3UlHZiohGClLqYBRW0NHavKJ0+X+5szRnzGtQ/I59plDBnx/n 6Ak1GSXcSxEqpXKkTOuUt9iKd+HLj+37RqRj9ei7/XoohS02h7EqbgmsKaxKE5xIkZSe t459XHYP4nnLrWta1kh4x/ccDRswlA+5pkK0E= Date: Tue, 26 Jan 2010 01:41:55 +0100 From: Frederic Weisbecker To: Masami Hiramatsu Cc: Mathieu Desnoyers , Steven Rostedt , Ingo Molnar , LKML , Li Zefan , Lai Jiangshan Subject: Re: [RFC PATCH 03/10] ftrace: Drop the ftrace_profile_enabled checks in tracing hot path Message-ID: <20100126004153.GJ5087@nowhere> References: <1264122982-1553-1-git-send-regression-fweisbec@gmail.com> <1264122982-1553-4-git-send-regression-fweisbec@gmail.com> <1264125917.31321.312.camel@gandalf.stny.rr.com> <20100122022858.GA2604@Krystal> <1264129978.31321.333.camel@gandalf.stny.rr.com> <20100122040959.GA11827@Krystal> <1264135966.31321.375.camel@gandalf.stny.rr.com> <20100122123450.GA19348@Krystal> <20100125205814.GD5087@nowhere> <4B5E17B8.4090002@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4B5E17B8.4090002@redhat.com> 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 Content-Length: 2756 Lines: 65 On Mon, Jan 25, 2010 at 05:14:16PM -0500, Masami Hiramatsu wrote: > Frederic Weisbecker wrote: > > On Fri, Jan 22, 2010 at 07:34:51AM -0500, Mathieu Desnoyers wrote: > >> * Steven Rostedt (rostedt@goodmis.org) wrote: > >>> On Thu, 2010-01-21 at 23:09 -0500, Mathieu Desnoyers wrote: > >>>> * Steven Rostedt (rostedt@goodmis.org) wrote: > >>> > >>>>> Hmm, interesting. Maybe something like that might work. But what if > >>>>> CONFIG_PREEMPT is enabled but CONFIG_FREEZER is not? > >>>> > >>>> Then you may want to make the function tracer depend on CONFIG_FREEZER, > >>>> but maybe Masami has other ideas ? > >>> > >>> egad no! This is just to help add guarantees to those that use the > >>> function tracer that when the tracing is disabled, it is guaranteed that > >>> no more tracing will be called by the function tracer. Currently, > >>> nothing relies on this. But we may add cases that might need this. > >> > >> Yep, identifying tracer quiescent state can become handy. > >> > >>> > >>> In fact, only those that need this requirement would need to do this > >>> trick. Anyway, we could make those depend on CONFIG_FREEZER, but that > >>> just seems to be a strange dependency. > >> > >> This makes me wonder (question for Masami)... > >> > >> static int __kprobes check_safety(void) > >> { > >> int ret = 0; > >> #if defined(CONFIG_PREEMPT) && defined(CONFIG_FREEZER) > >> ret = freeze_processes(); > >> if (ret == 0) { > >> struct task_struct *p, *q; > >> do_each_thread(p, q) { > >> if (p != current && p->state == TASK_RUNNING && > >> p->pid != 0) { > >> printk("Check failed: %s is running\n",p->comm); > >> ret = -1; > >> goto loop_end; > >> } > >> } while_each_thread(p, q); > > > > > > > > How does that deal with kernel threads that don't freeze? > > Hmm, right. It can't handle non-freezable kernel threads. > > > Also freezing every processes seems a bit of a heavy thing for that. > > Looks like a synchronize_tasks() would be really useful. > > Sure :-) > Maybe, I'd better remove booster support on preemptive kernel until then. I don't know as I haven't looked deeper into check_safety(), but does the fact we have non-freezable tasks break the assumptions that make kprobes booster safe? If so then yeah, may be deactivate it for now. -- 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/