Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752419AbaLLWmf (ORCPT ); Fri, 12 Dec 2014 17:42:35 -0500 Received: from mail-qa0-f41.google.com ([209.85.216.41]:35015 "EHLO mail-qa0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751429AbaLLWme (ORCPT ); Fri, 12 Dec 2014 17:42:34 -0500 Message-ID: <548B6F58.6010108@linaro.org> Date: Fri, 12 Dec 2014 17:42:32 -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> In-Reply-To: <20141210163817.GA27500@linaro.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/10/14 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. -dl -- 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/