From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754178AbYJAHyq (ORCPT ); Wed, 1 Oct 2008 03:54:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752395AbYJAHyh (ORCPT ); Wed, 1 Oct 2008 03:54:37 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:44034 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752132AbYJAHyg (ORCPT ); Wed, 1 Oct 2008 03:54:36 -0400 Date: Wed, 1 Oct 2008 09:54:19 +0200 From: Ingo Molnar To: Steven Rostedt Cc: Pekka Paalanen , linux-kernel@vger.kernel.org, Thomas Gleixner , Peter Zijlstra , Andrew Morton , Linus Torvalds , Mathieu Desnoyers , Frederic Weisbecker , Steven Rostedt Subject: Re: [PATCH 6/6] ftrace: take advantage of variable length entries Message-ID: <20081001075419.GA24509@elte.hu> References: <20080930030236.230994826@goodmis.org> <20080930030652.883661046@goodmis.org> <20080930203342.5b5ca814@daedalus.pq.iki.fi> 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 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Steven Rostedt wrote: > > > struct trace_entry *entry = iter->ent; > > > - struct mmiotrace_map *m = &entry->field.mmiomap; > > > + struct mmiotrace_map *m = (struct mmiotrace_map *)entry; > > > > This is different style than above, missing the struct > > trace_mmiotrace_map intermediate step. Looks like a bug, > > since struct mmiotrace_map is not the first field in > > struct trace_mmiotrace_map. > > Crap! yes this is a bug. Thanks for pointing this out. hm, there's a significant amount of type casts, see the grep below. The ringbuffer becoming type-opaque has exactly these kinds of dangers, and as i suggested a few days ago, please think about a debug mode that stores the record type in the trace entry and validates it on extraction or something like that. That might even be a robustness feature: the tracer should not crash if the trace buffer gets corrupted. ftrace had that invariant before, i think we should try to keep as many aspects of it as possible. Ingo -------------> ring_buffer.c: page = (struct buffer_page *)virt_to_page(addr); ring_buffer.c: cpu_buffer->reader_page = (struct buffer_page *)virt_to_page(addr); ring_buffer.c:static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer); ring_buffer.c: page = (struct buffer_page *)virt_to_page(addr); trace_boot.c: struct trace_boot *field = (struct trace_boot *)entry; trace.c:static DEFINE_PER_CPU(struct trace_array_cpu, global_trace_cpu); trace.c:static DEFINE_PER_CPU(struct trace_array_cpu, max_data); trace.c: cont = (struct trace_field_cont *)ent; trace.c: struct ftrace_entry *field = (struct ftrace_entry *)entry; trace.c: (struct ctx_switch_entry *)entry; trace.c: struct special_entry *field = (struct special_entry *)entry; trace.c: struct stack_entry *field = (struct stack_entry *)entry; trace.c: struct print_entry *field = (struct print_entry *)entry; trace.c: struct ftrace_entry *field = (struct ftrace_entry *)entry; trace.c: (struct ctx_switch_entry *)entry; trace.c: struct special_entry *field = (struct special_entry *)entry; trace.c: struct stack_entry *field = (struct stack_entry *)entry; trace.c: struct print_entry *field = (struct print_entry *)entry; trace.c: struct ftrace_entry *field = (struct ftrace_entry *)entry; trace.c: (struct ctx_switch_entry *)entry; trace.c: struct special_entry *field = (struct special_entry *)entry; trace.c: struct print_entry *field = (struct print_entry *)entry; trace.c: struct ftrace_entry *field = (struct ftrace_entry *)entry; trace.c: (struct ctx_switch_entry *)entry; trace.c: struct special_entry *field = (struct special_entry *)entry; trace.c: struct ftrace_entry *field = (struct ftrace_entry *)entry; trace.c: (struct ctx_switch_entry *)entry; trace.c: struct special_entry *field = (struct special_entry *)entry; trace.c: struct seq_file *m = (struct seq_file *)file->private_data; trace.c: offsetof(struct trace_iterator, seq)); trace.c: offsetof(struct trace_iterator, seq)); trace_mmiotrace.c: (struct trace_mmiotrace_rw *)entry; trace_mmiotrace.c: struct mmiotrace_map *m = (struct mmiotrace_map *)entry; trace_mmiotrace.c: struct print_entry *print = (struct print_entry *)entry; trace_sched_wakeup.c:static void __wakeup_reset(struct trace_array *tr); trace_sysprof.c:static DEFINE_PER_CPU(struct hrtimer, stack_trace_hrtimer); trace_sysprof.c: stack = ((char *)regs + sizeof(struct pt_regs)); trace_sysprof.c: regs = (struct pt_regs *)current->thread.sp0 - 1;