Re: [RFC PATCH for 4.17 02/21] rseq: Introduce restartable sequences system call (v12)

[Peter Zijlstra]

On Tue, Mar 27, 2018 at 12:05:23PM -0400, Mathieu Desnoyers wrote:
> +#ifdef CONFIG_RSEQ
> +	struct rseq __user *rseq;
> +	u32 rseq_len;
> +	u32 rseq_sig;
> +	/*
> +	 * RmW on rseq_event_mask must be performed atomically
> +	 * with respect to preemption.
> +	 */
> +	unsigned long rseq_event_mask;
> +#endif

> +static inline void rseq_signal_deliver(struct pt_regs *regs)
> +{
> +	set_bit(RSEQ_EVENT_SIGNAL_BIT, &current->rseq_event_mask);
> +	rseq_handle_notify_resume(regs);
> +}
> +
> +static inline void rseq_preempt(struct task_struct *t)
> +{
> +	set_bit(RSEQ_EVENT_PREEMPT_BIT, &t->rseq_event_mask);
> +	rseq_set_notify_resume(t);
> +}
> +
> +static inline void rseq_migrate(struct task_struct *t)
> +{
> +	set_bit(RSEQ_EVENT_MIGRATE_BIT, &t->rseq_event_mask);
> +	rseq_set_notify_resume(t);
> +}

Given that comment above, do you really need the full atomic set bit?
Isn't __set_bit() sufficient?