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

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Message-ID: <096752a7-21f9-8339-2e76-8c65859fa1d7@huawei.com>
Date:   Thu, 1 Apr 2021 16:49:47 +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 2021/3/31 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,
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.

BR,
Liao Chang
> 
> Thanks
> 
> 
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv
> .
> 

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