From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753515AbcDYFhb (ORCPT ); Mon, 25 Apr 2016 01:37:31 -0400 Received: from bh-25.webhostbox.net ([208.91.199.152]:52438 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752097AbcDYFh2 (ORCPT ); Mon, 25 Apr 2016 01:37:28 -0400 Subject: Re: next: suspicious RCU usage message since commit 'rcu: Remove superfluous versions of rcu_read_lock_sched_held()' To: paulmck@linux.vnet.ibm.com References: <20160424211424.GA20388@roeck-us.net> <20160424213147.GW3756@linux.vnet.ibm.com> <571D5D36.3060308@roeck-us.net> <20160425052847.GY3756@linux.vnet.ibm.com> Cc: Boqun Feng , Josh Triplett , Steven Rostedt , linux-kernel@vger.kernel.org From: Guenter Roeck Message-ID: <571DAD15.6070708@roeck-us.net> Date: Sun, 24 Apr 2016 22:37:25 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <20160425052847.GY3756@linux.vnet.ibm.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Authenticated_sender: linux@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: authenticated_id: linux@roeck-us.net X-Authenticated-Sender: bh-25.webhostbox.net: linux@roeck-us.net X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/24/2016 10:28 PM, Paul E. McKenney wrote: > On Sun, Apr 24, 2016 at 04:56:38PM -0700, Guenter Roeck wrote: >> Hi Paul, >> >> On 04/24/2016 02:31 PM, Paul E. McKenney wrote: >>> On Sun, Apr 24, 2016 at 02:14:24PM -0700, Guenter Roeck wrote: >>>> Hi, >>>> >>>> I see the following log message when running a qemu test for 'beagle' >>>> with omap2plus_defconfig. >>>> >>>> =============================== >>>> [ INFO: suspicious RCU usage. ] >>>> 4.6.0-rc4-next-20160422 #1 Not tainted >>>> ------------------------------- >>>> include/trace/events/power.h:328 suspicious rcu_dereference_check() usage! >>>> >>>> other info that might help us debug this: >>>> >>>> RCU used illegally from idle CPU! >>>> rcu_scheduler_active = 1, debug_locks = 0 >>>> RCU used illegally from extended quiescent state! >>>> no locks held by swapper/0/0. >>>> >>>> stack backtrace: >>>> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.6.0-rc4-next-20160422 #1 >>>> Hardware name: Generic OMAP3-GP (Flattened Device Tree) >>>> [] (unwind_backtrace) from [] (show_stack+0x10/0x14) >>>> [] (show_stack) from [] (dump_stack+0xa8/0xe0) >>>> [] (dump_stack) from [] (pwrdm_set_next_pwrst+0xf8/0x1cc) >>>> [] (pwrdm_set_next_pwrst) from [] (omap3_enter_idle_bm+0x1b8/0x1e8) >>>> [] (omap3_enter_idle_bm) from [] (cpuidle_enter_state+0x84/0x408) >>>> [] (cpuidle_enter_state) from [] (cpu_startup_entry+0x1c8/0x3f0) >>>> [] (cpu_startup_entry) from [] (start_kernel+0x354/0x3cc) >>>> >>>> bisect points to commit 'rcu: Remove superfluous versions of >>>> rcu_read_lock_sched_held()'. Bisect log is attached. >>> >>> I believe that the real fix is not a revert of that commit, but rather >>> that some of the tracing statements need an "_rcuidle" suffix. >>> >>> Something like the following (untested, probably does not build) patch. >>> >>> Thanx, Paul >>> >>> ------------------------------------------------------------------------ >>> >>> commit ca91304178e1cf53ee391236a0ac3969cc814e5f >>> Author: Paul E. McKenney >>> Date: Sun Apr 24 14:30:16 2016 -0700 >>> >>> arm: Use _rcuidle tracepoint to allow use from idle >>> >>> Signed-off-by: Paul E. McKenney >>> >>> diff --git a/arch/arm/mach-omap2/powerdomain.c b/arch/arm/mach-omap2/powerdomain.c >>> index 78af6d8cf2e2..12b66b5bcc55 100644 >>> --- a/arch/arm/mach-omap2/powerdomain.c >>> +++ b/arch/arm/mach-omap2/powerdomain.c >>> @@ -523,8 +523,8 @@ int pwrdm_set_next_pwrst(struct powerdomain *pwrdm, u8 pwrst) >>> >>> if (arch_pwrdm && arch_pwrdm->pwrdm_set_next_pwrst) { >>> /* Trace the pwrdm desired target state */ >>> - trace_power_domain_target(pwrdm->name, pwrst, >>> - smp_processor_id()); >>> + trace_power_domain_target_rcuidle(pwrdm->name, pwrst, >>> + smp_processor_id()); >>> /* Program the pwrdm desired target state */ >>> ret = arch_pwrdm->pwrdm_set_next_pwrst(pwrdm, pwrst); >>> } >>> >> >> It does build. After applying it, I get a different traceback. >> >> [] (unwind_backtrace) from [] (show_stack+0x10/0x14) >> [] (show_stack) from [] (dump_stack+0xa8/0xe0) >> [] (dump_stack) from [] (_pwrdm_state_switch+0x188/0x32c) >> [] (_pwrdm_state_switch) from [] (_pwrdm_post_transition_cb+0xc/0x14) >> [] (_pwrdm_post_transition_cb) from [] (pwrdm_for_each+0x30/0x5c) >> [] (pwrdm_for_each) from [] (pwrdm_post_transition+0x24/0x30) >> [] (pwrdm_post_transition) from [] (omap_sram_idle+0xfc/0x240) >> [] (omap_sram_idle) from [] (omap3_enter_idle_bm+0xf0/0x1e8) >> [] (omap3_enter_idle_bm) from [] (cpuidle_enter_state+0x84/0x408) >> [] (cpuidle_enter_state) from [] (cpu_startup_entry+0x1c8/0x3f0) >> [] (cpu_startup_entry) from [] (start_kernel+0x354/0x3cc) >> >> After making the same change in _pwrdm_state_switch(), the traceback is gone >> from my tests (beagle, beagle-xm, and overo-tobi). > > Very good! > > (And yes, you normally find these one at a time...) > Are you going to submit a formal patch ? Thanks, Guenter