Re: [PATCH -tip] x86: kprobes: Cleanup preempt disabling and enabling

From: Ingo Molnar
Date: Sat Mar 03 2018 - 05:00:36 EST



* Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:

> +/*
> + * Interrupts are disabled on entry as trap3 is an interrupt gate and they
> + * remain disabled throughout this function.
> + */
> +int kprobe_int3_handler(struct pt_regs *regs)
> +{
> + struct kprobe_ctlblk *kcb;
> + int ret;
> +
> + if (user_mode(regs))
> + return 0;
> +
> + /*
> + * We don't want to be preempted for the entire
> + * duration of kprobe processing.
> + */
> + preempt_disable();
> +
> + kcb = get_kprobe_ctlblk();
> + ret = kprobe_int3_dispatcher(regs, kcb);
> +
> + if (!kprobe_ready_for_singlestep(regs))
> + preempt_enable_no_resched();
> +
> + return ret;

What's the point of disabling preemption, if IRQs are disabled already?

There's no preemption when IRQs are off...

Thanks,

Ingo