From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751641AbbFRBtu (ORCPT ); Wed, 17 Jun 2015 21:49:50 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:41196 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750724AbbFRBtk (ORCPT ); Wed, 17 Jun 2015 21:49:40 -0400 Message-ID: <558223B2.5030204@codeaurora.org> Date: Wed, 17 Jun 2015 18:49:38 -0700 From: Stephen Boyd User-Agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com CC: John Stultz , Nicolas Pitre , Steven Rostedt , lkml Subject: Re: Suspicious RCU usage at boot w/ arm ipi trace events? References: <20150617003154.GV3913@linux.vnet.ibm.com> <5580C239.4060707@codeaurora.org> <20150617044643.GW3913@linux.vnet.ibm.com> In-Reply-To: <20150617044643.GW3913@linux.vnet.ibm.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/16/2015 09:46 PM, Paul E. McKenney wrote: > On Tue, Jun 16, 2015 at 05:41:29PM -0700, Stephen Boyd wrote: >> >> The tracepoint 'trace_ipi_entry' in handle_IPI() is using RCU and we >> haven't called irq_enter() yet at the point. Does this tracepoint need >> to have _rcuidle() added to it? > Yes, I believe that would fix this problem. > Ok... here's the patch. I see the problem on my device and applying this patch fixes it. ----8<---- From: Stephen Boyd Subject: [PATCH] ARM: smp: Silence suspicious RCU usage with ipi tracepoints John Stultz reports an RCU splat on boot with ARM ipi trace events enabled. =============================== [ INFO: suspicious RCU usage. ] 4.1.0-rc7-00033-gb5bed2f #153 Not tainted ------------------------------- include/trace/events/ipi.h:68 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 4.1.0-rc7-00033-gb5bed2f #153 Hardware name: Qualcomm (Flattened Device Tree) [] (unwind_backtrace) from [] (show_stack+0x10/0x14) [] (show_stack) from [] (dump_stack+0x70/0xbc) [] (dump_stack) from [] (handle_IPI+0x428/0x604) [] (handle_IPI) from [] (gic_handle_irq+0x54/0x5c) [] (gic_handle_irq) from [] (__irq_svc+0x44/0x7c) Exception stack(0xc09f3f48 to 0xc09f3f90) 3f40: 00000001 00000001 00000000 c09f73b8 c09f4528 c0a5de9c 3f60: c076b4f0 00000000 00000000 c09ef108 c0a5cec1 00000001 00000000 c09f3f90 3f80: c026bf60 c0210ab8 20000113 ffffffff [] (__irq_svc) from [] (arch_cpu_idle+0x20/0x3c) [] (arch_cpu_idle) from [] (cpu_startup_entry+0x2c0/0x5dc) [] (cpu_startup_entry) from [] (start_kernel+0x358/0x3c4) [] (start_kernel) from [<8020807c>] (0x8020807c) At this point in the IPI handling path we haven't called irq_enter() yet, so RCU doesn't know that we're about to exit idle and properly warns that we're using RCU from an idle CPU. Use trace_ipi_entry_rcuidle() instead of trace_ipi_entry() so that RCU is informed about our exit from idle. Reported-by: John Stultz Fixes: 365ec7b17327 "ARM: add IPI tracepoints" Signed-off-by: Stephen Boyd --- arch/arm/kernel/smp.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c index 13a91d390832..03eb8a446dca 100644 --- a/arch/arm/kernel/smp.c +++ b/arch/arm/kernel/smp.c @@ -589,7 +589,7 @@ void handle_IPI(int ipinr, struct pt_regs *regs) struct pt_regs *old_regs = set_irq_regs(regs); if ((unsigned)ipinr < NR_IPI) { - trace_ipi_entry(ipi_types[ipinr]); + trace_ipi_entry_rcuidle(ipi_types[ipinr]); __inc_irq_stat(cpu, ipi_irqs[ipinr]); } @@ -648,7 +648,7 @@ void handle_IPI(int ipinr, struct pt_regs *regs) } if ((unsigned)ipinr < NR_IPI) - trace_ipi_exit(ipi_types[ipinr]); + trace_ipi_exit_rcuidle(ipi_types[ipinr]); set_irq_regs(old_regs); } -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project