From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932159AbbFSSuN (ORCPT ); Fri, 19 Jun 2015 14:50:13 -0400 Received: from smtp.codeaurora.org ([198.145.29.96]:44671 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753435AbbFSSt4 (ORCPT ); Fri, 19 Jun 2015 14:49:56 -0400 Date: Fri, 19 Jun 2015 11:49:55 -0700 From: Stephen Boyd To: John Stultz Cc: Paul McKenney , Nicolas Pitre , Steven Rostedt , lkml Subject: Re: Suspicious RCU usage at boot w/ arm ipi trace events? Message-ID: <20150619184955.GE22132@codeaurora.org> References: <20150617003154.GV3913@linux.vnet.ibm.com> <5580C239.4060707@codeaurora.org> <20150617044643.GW3913@linux.vnet.ibm.com> <558223B2.5030204@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/18, John Stultz wrote: > On Wed, Jun 17, 2015 at 6:49 PM, Stephen Boyd wrote: > > 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); > > } > > > > Tested-by: John Stultz > > Thanks for fixing this up! Thanks. I'll throw it into the patch tracker. I'll send the same patch for arm64 because I assume it's also broken there. -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in Please read the FAQ at http://www.tux.org/lkml/