Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753898AbYKFHoq (ORCPT ); Thu, 6 Nov 2008 02:44:46 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752813AbYKFHoa (ORCPT ); Thu, 6 Nov 2008 02:44:30 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:45928 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754023AbYKFHo3 (ORCPT ); Thu, 6 Nov 2008 02:44:29 -0500 Date: Thu, 6 Nov 2008 08:44:17 +0100 From: Ingo Molnar To: Ken Chen Cc: Linux Kernel Mailing List , Peter Zijlstra , Steven Rostedt Subject: Re: [patch] sched: fix single-depth wchan output Message-ID: <20081106074417.GB8459@elte.hu> References: <20081106061125.GA6384@elte.hu> <20081106063012.GA15731@elte.hu> <20081106065925.GE15731@elte.hu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00,DNS_FROM_SECURITYSAGE autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] 0.0 DNS_FROM_SECURITYSAGE RBL: Envelope sender in blackholes.securitysage.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2229 Lines: 60 * Ken Chen wrote: > On Wed, Nov 5, 2008 at 10:59 PM, Ingo Molnar wrote: > > If it does stack walking manually then please update it to use > > save_stack_trace() instead - that is the standard API that will > > utilize the best possible stack walking machinery on the architecture > > level. > > OK, I pulled the patch out of our code that export stack trace via > /proc/pid/trace. I didn't write this patch, but I think a better > choice would be to override struct stacktrace_ops print_trace_ops > with a memory buffer pointer to dump the stack into. If you have > any comments, please let me know. I will polish this patch up and > rebase to git-head. hm, instead of modifying the lowlevel arch dump code, why not just use the existing save_stack_trace(), and render the output yourself via a trivial sprintf, just like kernel/lockdep.c does? See kernel/stacktrace.c's print_stack_trace() - that could be extended with a sprintf_stack_trace() method. Allocate a large enough buffer dynamically, with a max of 128 stacktrace entries or so. (the output buffer is limited to 4K-ish anyway, right?) As a bonus this will work on every architecture, not just x86. a few other details: > - char namebuf[KSYM_NAME_LEN]; > + char namebuf[128]; ... time machine back to old crappy code ;-) > symname = kallsyms_lookup(address, &symsize, &offset, > - &modname, namebuf); > + &modname, namebuf); ditto. But none of this has to be modified so you can just drop these bits. > + read_lock(&tasklist_lock); > + buf_show_task(posp, end, task); > + read_unlock(&tasklist_lock); to get a stable trace we'll need more locking than that (tasklist_lock does not exclude scheduling, etc.) - but it takes care of the most important detail: tasks exiting from under us. So this should be OK. > #endif > + INF("trace", S_IFREG|S_IRUGO, pid_trace), that needs to be r-------- instead of r--r--r--, for security reasons. Ingo -- 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/