From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753339AbcDYF2T (ORCPT ); Mon, 25 Apr 2016 01:28:19 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:54457 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751495AbcDYF2R (ORCPT ); Mon, 25 Apr 2016 01:28:17 -0400 X-IBM-Helo: d03dlp03.boulder.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Date: Sun, 24 Apr 2016 22:28:47 -0700 From: "Paul E. McKenney" To: Guenter Roeck Cc: Boqun Feng , Josh Triplett , Steven Rostedt , linux-kernel@vger.kernel.org Subject: Re: next: suspicious RCU usage message since commit 'rcu: Remove superfluous versions of rcu_read_lock_sched_held()' Message-ID: <20160425052847.GY3756@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20160424211424.GA20388@roeck-us.net> <20160424213147.GW3756@linux.vnet.ibm.com> <571D5D36.3060308@roeck-us.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <571D5D36.3060308@roeck-us.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16042505-8236-0000-0000-000026CA2AF6 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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...) Thanx, Paul