From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752115AbcBLRiy (ORCPT ); Fri, 12 Feb 2016 12:38:54 -0500 Received: from mail-pa0-f43.google.com ([209.85.220.43]:33082 "EHLO mail-pa0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751273AbcBLRix (ORCPT ); Fri, 12 Feb 2016 12:38:53 -0500 Subject: Re: [PATCH] arm64: make irq_stack_ptr more robust To: James Morse , will.deacon@arm.com References: <1455227590-9837-1-git-send-email-yang.shi@linaro.org> <56BDE260.20504@arm.com> Cc: catalin.marinas@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linaro-kernel@lists.linaro.org From: "Shi, Yang" Message-ID: <56BE18AB.4090902@linaro.org> Date: Fri, 12 Feb 2016 09:38:51 -0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <56BDE260.20504@arm.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/12/2016 5:47 AM, James Morse wrote: > 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") Wii add in v2. > > >> 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" Will fix in v2. > > >> + * 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()) I tried to build the kernel with preempt and without preempt, both works. And, I saw arch/arm64/include/asm/Kbuild has: generic-y += preempt.h So, it sounds preempt.h has been included by default. Thanks, Yang > > > Acked-by: James Morse > Tested-by: James Morse > > > Thanks! > > James > >