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

[Peter Zijlstra]

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.