Re: [RFC PATCH v7 1/7] Restartable sequences system call

On Tue, Aug 09, 2016 at 10:41:47PM +0000, Mathieu Desnoyers wrote:

#ifdef __LP64__

static bool rseq_update_cpu_id_event_counter(struct task_struct *t)
{
        union rseq_cpu_event u;

        u.e.cpu_id = raw_smp_processor_id();
        u.e.event_counter = ++t->rseq_event_counter;
        if (__put_user(u.v, &t->rseq->u.v))
                return false;
        trace_rseq_inc(t->rseq_event_counter);
        return true;
}

#else /* #ifdef __LP64__ */

static bool rseq_update_cpu_id_event_counter(struct task_struct *t)
{
        if (__put_user(raw_smp_processor_id(), &t->rseq->u.e.cpu_id))
                return false;
        if (__put_user(++t->rseq_event_counter, &t->rseq->u.e.event_counter))
                return false;
        trace_rseq_inc(t->rseq_event_counter);
        return true;
}

#endif /* #else #ifdef __LP64__ */

I don't think you need to guard it (and CONFIG_64BIT is the 'right'
kernel symbol for that), 32bit should have u64 __put_user() only
implemented as 2 u32 stores.