From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933027AbbCPVb7 (ORCPT ); Mon, 16 Mar 2015 17:31:59 -0400 Received: from smtprelay0021.hostedemail.com ([216.40.44.21]:37887 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932524AbbCPVb5 convert rfc822-to-8bit (ORCPT ); Mon, 16 Mar 2015 17:31:57 -0400 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 30,2,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::::::::,RULES_HIT:41:152:355:379:541:800:960:968:973:988:989:1260:1277:1311:1313:1314:1345:1437:1513:1515:1516:1518:1521:1534:1542:1593:1594:1711:1730:1747:1777:1792:1981:2194:2199:2393:2553:2559:2562:2893:2897:2904:3138:3139:3140:3141:3142:3352:3865:3866:3867:3868:3871:3872:3874:4321:5007:6261:7903:8660:9040:10010:10400:10848:11026:11473:11658:11914:12043:12114:12438:12517:12519:12555:13148:13161:13221:13229:13230:14096:14097:21080:21088,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:1:0 X-HE-Tag: badge87_4aff23a64b242 X-Filterd-Recvd-Size: 3594 Date: Mon, 16 Mar 2015 17:31:54 -0400 From: Steven Rostedt To: LKML Cc: Ingo Molnar , Thomas Gleixner , Christoph Lameter , "H. Peter Anvin" , Uwe =?UTF-8?B?S2xlaW5lLUvDtm5pZw==?= , linux-arm-kernel@lists.infradead.org, Russell King Subject: [RFC][PATCH] ring-buffer: Replace this_cpu_{read,write} with this_cpu_ptr() Message-ID: <20150316173154.537b80ee@gandalf.local.home> X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.25; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It has come to my attention that this_cpu_read/write are horrible on architectures other than x86. Worse yet, they actually disable preemption or interrupts! This caused some unexpected tracing results on ARM. 101.356868: preempt_count_add <-ring_buffer_lock_reserve 101.356870: preempt_count_sub <-ring_buffer_lock_reserve The ring_buffer_lock_reserve has recursion protection that requires accessing a per cpu variable. But since preempt_disable() is traced, it too got traced while accessing the variable that is suppose to prevent recursion like this. The generic version of this_cpu_read() and write() are: #define _this_cpu_generic_read(pcp) \ ({ typeof(pcp) ret__; \ preempt_disable(); \ ret__ = *this_cpu_ptr(&(pcp)); \ preempt_enable(); \ ret__; \ }) #define _this_cpu_generic_to_op(pcp, val, op) \ do { \ unsigned long flags; \ raw_local_irq_save(flags); \ *__this_cpu_ptr(&(pcp)) op val; \ raw_local_irq_restore(flags); \ } while (0) Which is unacceptable for locations that know they are within preempt disabled or interrupt disabled locations. I may go and remove all this_cpu_read,write() calls from my code because of this. Cc: stable@vger.kernel.org Cc: Christoph Lameter Reported-by: Uwe Kleine-König Signed-off-by: Steven Rostedt --- diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 5040d44fe5a3..be33c6093ca5 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2679,7 +2679,11 @@ static DEFINE_PER_CPU(unsigned int, current_context); static __always_inline int trace_recursive_lock(void) { - unsigned int val = this_cpu_read(current_context); + /* + * We can not use this_cpu_read() and this_cpu_write() because + * the generic versions call preempt_disable() + */ + unsigned int val = *this_cpu_ptr(¤t_context); int bit; if (in_interrupt()) { @@ -2696,18 +2700,18 @@ static __always_inline int trace_recursive_lock(void) return 1; val |= (1 << bit); - this_cpu_write(current_context, val); + *this_cpu_ptr(¤t_context) = val; return 0; } static __always_inline void trace_recursive_unlock(void) { - unsigned int val = this_cpu_read(current_context); + unsigned int val = *this_cpu_ptr(¤t_context); val--; val &= this_cpu_read(current_context); - this_cpu_write(current_context, val); + *this_cpu_ptr(¤t_context) = val; } #else