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    SubjectRe: [PATCH v3 0/5] ARM64: Add kernel probes(Kprobes) support
    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 <steve.capper@linaro.org>
    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;
    }
    --
    1.9.3


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