Re: [PATCH v8 10/15] x86/split_lock: Handle #AC exception for split lock

[Thomas Gleixner]

On Wed, 24 Apr 2019, Fenghua Yu wrote:

> +void handle_split_lock_kernel_mode(void)

....

> +dotraplinkage void do_alignment_check(struct pt_regs *regs, long error_code)
> +{
> +	unsigned int trapnr = X86_TRAP_AC;
> +	char str[] = "alignment check";
> +	int signr = SIGBUS;
> +
> +	RCU_LOCKDEP_WARN(!rcu_is_watching(), "entry code didn't wake RCU");
> +
> +	if (notify_die(DIE_TRAP, str, regs, error_code, trapnr, signr) ==
> +		       NOTIFY_STOP)
> +		return;
> +
> +	cond_local_irq_enable(regs);
> +	if (!user_mode(regs) &&
> +	    static_cpu_has(X86_FEATURE_SPLIT_LOCK_DETECT)) {
> +		/*
> +		 * Only split lock can generate #AC from kernel at this point.
> +		 * Warn and disable split lock detection on this CPU. The
> +		 * faulting instruction will be executed without generating
> +		 * another #AC fault.
> +		 */
> +		return handle_split_lock_kernel_mode();

return fun()? For some reason gcc will not complain about that, but for the
reader it's confusing at best.

Thanks,

	tglx