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

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Date:   Fri, 2 Apr 2021 21:32:06 +0800
From:   Jisheng Zhang <jszhang3@...l.ustc.edu.cn>
To:     "liaochang (A)" <liaochang1@...wei.com>
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

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