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

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Date:   Wed, 31 Mar 2021 22:22:44 +0800
From:   Jisheng Zhang <jszhang3@...l.ustc.edu.cn>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     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 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()

Thanks