linux-kernel - Re: [PATCH] riscv: keep interrupts disabled for BREAKPOINT exception

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Date:   Tue, 6 Apr 2021 15:27:51 +0800
From:   "liaochang (A)" <liaochang1@...wei.com>
To:     Jisheng Zhang <jszhang3@...l.ustc.edu.cn>
CC:     Masami Hiramatsu <mhiramat@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Guo Ren <guoren@...ux.alibaba.com>,
        <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] riscv: keep interrupts disabled for BREAKPOINT exception

Hi Jisheng,

在 2021/4/2 21:32, Jisheng Zhang 写道:
> On Thu, 1 Apr 2021 16:49:47 +0800
> "liaochang (A)" <liaochang1@...wei.com> wrote:
> 
>> Hi Jisheng,
> 
> Hi,
> 
>>
>> 在 2021/3/31 22:22, Jisheng Zhang 写道:
>>> On Tue, 30 Mar 2021 18:33:16 +0900
>>> Masami Hiramatsu <mhiramat@...nel.org> wrote:
>>>   
>>>> Hi Jisheng,  
>>>
>>> Hi Masami,
>>>   
>>>>
>>>> On Tue, 30 Mar 2021 02:16:24 +0800
>>>> Jisheng Zhang <jszhang3@...l.ustc.edu.cn> wrote:
>>>>  
>>>>> From: Jisheng Zhang <jszhang@...nel.org>
>>>>>
>>>>> Current riscv's kprobe handlers are run with both preemption and
>>>>> interrupt enabled, this violates kprobe requirements. Fix this issue
>>>>> by keeping interrupts disabled for BREAKPOINT exception.    
>>>>
>>>> Not only while the breakpoint exception but also until the end of
>>>> the single step (maybe you are using __BUG_INSN_32 ??) need to be
>>>> disable interrupts. Can this do that?
>>>>  
>>>
>>> interrupt is disabled during "single step" by kprobes_save_local_irqflag()
>>> and kprobes_restore_local_irqflag(). The code flow looks like: 
>>>
>>> do_trap_break()   // for bp
>>>   kprobe_breakpoint_handler()
>>>     setup_singlestep()
>>>       kprobes_restore_local_irqflag()
>>>
>>> do_trap_break()  // for ss
>>>   kprobe_single_step_handler()
>>>     kprobes_restore_local_irqflag()  
>>
>> Recently, kernel hit BUG_ON() on QEMU after I install a probe at "sys_read" via kprobe,
> 
> TIPS: Each line should not exceed 80 chars
> 
>> accoriding to my debugging and analysis it looks like caused by the "irq disable" operation for single-stepping.
>>
>> I present a detailed description about this problem in the mail with title "[PATCH] riscv/kprobe: fix kernel panic when invoking sys_read traced by kprobe".
>> Looking forward to some feedback,Thanks.
>>
> 
> I will comment that patch.

Thanks for your reminder.

> 
> thanks
> 
> .
>