Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752837AbaLLXKX (ORCPT ); Fri, 12 Dec 2014 18:10:23 -0500 Received: from mail-yh0-f52.google.com ([209.85.213.52]:62959 "EHLO mail-yh0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751911AbaLLXKW (ORCPT ); Fri, 12 Dec 2014 18:10:22 -0500 MIME-Version: 1.0 In-Reply-To: <548B6F58.6010108@linaro.org> 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> Date: Fri, 12 Dec 2014 23:10:21 +0000 Message-ID: Subject: Re: [PATCH v3 0/5] ARM64: Add kernel probes(Kprobes) support From: Steve Capper To: David Long 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" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 will think about MDSCR_EL1, when I'm awake :-). Cheers, -- Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/