Re: [PATCH] arm64: reenable interrupt when handling ptrace breakpoint

[Thomas Gleixner]

On Mon, 21 Dec 2015, Will Deacon wrote:
> +static void send_user_sigtrap(int si_code)
> +{
> +	struct pt_regs *regs = current_pt_regs();
> +	siginfo_t info = {
> +		.si_signo	= SIGTRAP,
> +		.si_errno	= 0,
> +		.si_code	= si_code,
> +		.si_addr	= (void __user *)instruction_pointer(regs),
> +	};
> +
> +	if (WARN_ON(!user_mode(regs)))
> +		return;
> +
> +	preempt_disable();

That doesn't work on RT either. force_sig_info() takes task->sighand->siglock,
which is a 'sleeping' spinlock on RT.

Why would we need to disable preemption here at all? What's the problem of
being preempted or even migrated?

Thanks,

	tglx
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