From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751451AbaLOG33 (ORCPT ); Mon, 15 Dec 2014 01:29:29 -0500 Received: from mail-qc0-f172.google.com ([209.85.216.172]:49372 "EHLO mail-qc0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750801AbaLOG31 (ORCPT ); Mon, 15 Dec 2014 01:29:27 -0500 Message-ID: <548E7FC0.3090506@linaro.org> Date: Mon, 15 Dec 2014 01:29:20 -0500 From: David Long User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.2.0 MIME-Version: 1.0 To: Steve Capper CC: Masami Hiramatsu , "Jon Medhurst (Tixy)" , Russell King , Ananth N Mavinakayanahalli , Sandeepa Prabhu , Catalin Marinas , Will Deacon , "linux-kernel@vger.kernel.org" , Anil S Keshavamurthy , William Cohen , David Miller , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v3 0/5] ARM64: Add kernel probes(Kprobes) support References: <547F242D.1060705@redhat.com> <547F94B0.1000902@linaro.org> <547FB5DD.901@redhat.com> <547FCB73.1010707@linaro.org> <54803ADD.2090201@hitachi.com> <54804B1F.3020703@hitachi.com> <20141209133340.GA20265@linaro.org> <548706C6.2050105@linaro.org> <20141210163817.GA27500@linaro.org> <548B6F58.6010108@linaro.org> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/12/14 18:10, Steve Capper wrote: > On 12 December 2014 at 22:42, David Long wrote: >> On 12/10/14 11:38, Steve Capper wrote: >>> >>> On Tue, Dec 09, 2014 at 09:27:18AM -0500, David Long wrote: >>>> >>>> On 12/09/14 08:33, Steve Capper wrote: >>>>> >>>>> On Thu, Dec 04, 2014 at 08:53:03PM +0900, Masami Hiramatsu wrote: >>> >>> >>> [...] >>> >>>>> >>>>> Not sure if this is helpful, but the following also caused a crash for >>>>> me: >>>>> >>>>> echo "p:trace_event_buffer_lock_reserve trace_event_buffer_lock_reserve" >>>>>> /sys/kernel/debug/tracing/kprobe_events >>>>> echo "p:memcpy memcpy" >> /sys/kernel/debug/tracing/kprobe_events >>>>> echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable >>>>> >>>>> [immediate crash] >>>>> >>>>> The crash point for me is in the arm64 ASID allocator, it again looks >>>>> like the interrupts are in an unexpected state. >>>>> (check_and_switch_context goes down the irqs disabled code path, I >>>>> think incorrectly). >>>>> >>>>> This occurred for me both with and without the proposed irq saving fix. >>>>> >>>>> I will do some more digging. >>>>> >>>> >>>> Thanks, more information is good. >>>> >>> >>> Hi, >>> >>> Some good news, I think I've fixed the problem I've been experiencing. >>> >>> Basically, I've torn out all the interrupt save/restore and have >>> narrowed the scope to just sandwich the instruction single-step. This >>> simplifies a lot of logic, and I've now been able to perf record a >>> kprobe on memcpy (and the trace_event_buffer_lock_reserve + memcpy >>> test) without any issues on a Juno platform. >>> >>> I may have been somewhat over-zealous with the chainsaw, so please do >>> put this fix through its paces. >>> >>> Cheers, >>> -- >>> Steve >>> >>> >>> From d3f4d80ce19bec71bd03209beb2fbfd8084d6543 Mon Sep 17 00:00:00 2001 >>> From: Steve Capper >>> Date: Mon, 1 Dec 2014 11:30:10 +0000 >>> Subject: [PATCH] Fix the interrupt handling for kprobes >>> >>> --- >>> arch/arm64/kernel/kprobes.c | 16 ++-------------- >>> 1 file changed, 2 insertions(+), 14 deletions(-) >>> >>> diff --git a/arch/arm64/kernel/kprobes.c b/arch/arm64/kernel/kprobes.c >>> index be7c330..d39d826 100644 >>> --- a/arch/arm64/kernel/kprobes.c >>> +++ b/arch/arm64/kernel/kprobes.c >>> @@ -229,10 +229,6 @@ skip_singlestep_missed(struct kprobe_ctlblk *kcb, >>> struct pt_regs *regs) >>> { >>> /* set return addr to next pc to continue */ >>> instruction_pointer(regs) += sizeof(kprobe_opcode_t); >>> - >>> - if (kcb->kprobe_status != KPROBE_REENTER) >>> - kprobes_restore_local_irqflag(regs); >>> - >>> } >>> >>> static void __kprobes setup_singlestep(struct kprobe *p, >>> @@ -259,7 +255,7 @@ static void __kprobes setup_singlestep(struct kprobe >>> *p, >>> spsr_set_debug_flag(regs, 0); >>> >>> /* IRQs and single stepping do not mix well. */ >>> - local_irq_disable(); >>> + kprobes_save_local_irqflag(regs); >>> kernel_enable_single_step(regs); >>> instruction_pointer(regs) = slot; >>> } else { >>> @@ -326,7 +322,6 @@ post_kprobe_handler(struct kprobe_ctlblk *kcb, struct >>> pt_regs *regs) >>> } >>> >>> reset_current_kprobe(); >>> - kprobes_restore_local_irqflag(regs); >>> } >>> >>> int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int >>> fsr) >>> @@ -380,8 +375,6 @@ int __kprobes kprobe_fault_handler(struct pt_regs >>> *regs, unsigned int fsr) >>> return 1; >>> >>> break; >>> - default: >>> - break; >>> } >>> return 0; >>> } >>> @@ -446,7 +439,6 @@ void __kprobes kprobe_handler(struct pt_regs *regs) >>> * handling of this interrupt is appropriate. >>> * Return back to original instruction, and continue. >>> */ >>> - kprobes_restore_local_irqflag(regs); >>> return; >>> } else if (cur) { >>> /* We probably hit a jprobe. Call its break handler. */ >>> @@ -459,7 +451,6 @@ void __kprobes kprobe_handler(struct pt_regs *regs) >>> /* breakpoint is removed, now in a race >>> * Return back to original instruction & continue. >>> */ >>> - kprobes_restore_local_irqflag(regs); >>> } >>> } >>> >>> @@ -485,6 +476,7 @@ kprobe_single_step_handler(struct pt_regs *regs, >>> unsigned int esr) >>> retval = kprobe_ss_hit(kcb, instruction_pointer(regs)); >>> >>> if (retval == DBG_HOOK_HANDLED) { >>> + kprobes_restore_local_irqflag(regs); >>> kernel_disable_single_step(); >>> >>> if (kcb->kprobe_status == KPROBE_REENTER) >>> @@ -499,7 +491,6 @@ kprobe_single_step_handler(struct pt_regs *regs, >>> unsigned int esr) >>> static int __kprobes >>> kprobe_breakpoint_handler(struct pt_regs *regs, unsigned int esr) >>> { >>> - kprobes_save_local_irqflag(regs); >>> kprobe_handler(regs); >>> return DBG_HOOK_HANDLED; >>> } >>> @@ -563,7 +554,6 @@ int __kprobes longjmp_break_handler(struct kprobe *p, >>> struct pt_regs *regs) >>> memcpy((void *)stack_addr, kcb->jprobes_stack, >>> MIN_STACK_SIZE(stack_addr)); >>> preempt_enable_no_resched(); >>> - kprobes_restore_local_irqflag(regs); >>> return 1; >>> } >>> return 0; >>> @@ -655,8 +645,6 @@ trampoline_probe_handler(struct kprobe *p, struct >>> pt_regs *regs) >>> kfree(ri); >>> } >>> >>> - kprobes_restore_local_irqflag(regs); >>> - >>> /* return 1 so that post handlers not called */ >>> return 1; >>> } >>> >> >> Sorry for the delay in responding. The assumption with the existing code is >> that you can't enable single-stepping in MDSCR until you disable interrupts. >> But since we get to that point (in this case) with debug exceptions masked >> in daif I suppose this is an unnecessary constraint, as you have >> demonstrated. I do actually wonder if we need to set the bit in MDSCR_EL1 >> at all since we're also setting it in the spsr in the regs structure that >> will be restored when the eret is done, but it looks like >> kernel_enable_single_step() sets both. >> > > I do think we need to disable interrupts, but only when we're about to > single-step. > (My explanation before was imprecise, apologies). > The change I posted disables interrupts in __kprobes_single_step, and > restores them in kprobe_single_step_handler. > I did try removing the interrupt logic completely, but this then > resulted in a system hang after a few seconds. > I worded that badly. You still have to disable interrupts but I had thought we needed to do that before setting SS in MDSCR. You've shown we can do it anytime before we unmask debug exceptions. > I will think about MDSCR_EL1, when I'm awake :-). > > Cheers, > -- > Steve >