From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752731AbcBLNsb (ORCPT ); Fri, 12 Feb 2016 08:48:31 -0500 Received: from foss.arm.com ([217.140.101.70]:32896 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752424AbcBLNs1 (ORCPT ); Fri, 12 Feb 2016 08:48:27 -0500 Message-ID: <56BDE260.20504@arm.com> Date: Fri, 12 Feb 2016 13:47:12 +0000 From: James Morse User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.6.0 MIME-Version: 1.0 To: Yang Shi , will.deacon@arm.com CC: catalin.marinas@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linaro-kernel@lists.linaro.org Subject: Re: [PATCH] arm64: make irq_stack_ptr more robust References: <1455227590-9837-1-git-send-email-yang.shi@linaro.org> In-Reply-To: <1455227590-9837-1-git-send-email-yang.shi@linaro.org> 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 Hi! On 11/02/16 21:53, Yang Shi wrote: > Switching between stacks is only valid if we are tracing ourselves while on the > irq_stack, so it is only valid when in current and non-preemptible context, > otherwise is is just zeroed off. Given it was picked up with CONFIG_DEBUG_PREEMPT: Fixes: 132cd887b5c5 ("arm64: Modify stack trace and dump for use with irq_stack") > Signed-off-by: Yang Shi > --- > arch/arm64/kernel/stacktrace.c | 13 ++++++------- > arch/arm64/kernel/traps.c | 11 ++++++++++- > 2 files changed, 16 insertions(+), 8 deletions(-) > > diff --git a/arch/arm64/kernel/stacktrace.c b/arch/arm64/kernel/stacktrace.c > index 12a18cb..d9751a4 100644 > --- a/arch/arm64/kernel/stacktrace.c > +++ b/arch/arm64/kernel/stacktrace.c > @@ -44,14 +44,13 @@ int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame) > unsigned long irq_stack_ptr; > > /* > - * Use raw_smp_processor_id() to avoid false-positives from > - * CONFIG_DEBUG_PREEMPT. get_wchan() calls unwind_frame() on sleeping > - * task stacks, we can be pre-empted in this case, so > - * {raw_,}smp_processor_id() may give us the wrong value. Sleeping > - * tasks can't ever be on an interrupt stack, so regardless of cpu, > - * the checks will always fail. > + * Switching between stacks is valid when tracing current and in > + * non-preemptible context. > */ > - irq_stack_ptr = IRQ_STACK_PTR(raw_smp_processor_id()); > + if (tsk == current && !preemptible()) > + irq_stack_ptr = IRQ_STACK_PTR(smp_processor_id()); > + else > + irq_stack_ptr = 0; > > low = frame->sp; > /* irq stacks are not THREAD_SIZE aligned */ > diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c > index cbedd72..7d8db3a 100644 > --- a/arch/arm64/kernel/traps.c > +++ b/arch/arm64/kernel/traps.c > @@ -146,9 +146,18 @@ static void dump_instr(const char *lvl, struct pt_regs *regs) > static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk) > { > struct stackframe frame; > - unsigned long irq_stack_ptr = IRQ_STACK_PTR(smp_processor_id()); > + unsigned long irq_stack_ptr; > int skip; > > + /* > + * Switching between stacks is valid when tracing current and in Nit: Two spaces: "between[ ][ ]stacks" > + * non-preemptible context. > + */ > + if (tsk == current && !preemptible()) > + irq_stack_ptr = IRQ_STACK_PTR(smp_processor_id()); > + else > + irq_stack_ptr = 0; > + > pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk); > > if (!tsk) > Neither file includes 'linux/preempt.h' for the definition of preemptible(). (I can't talk: I should have included smp.h for smp_processor_id()) Acked-by: James Morse Tested-by: James Morse Thanks! James