On Tue, Jul 03, 2018 at 02:15:34PM -0400, Mathieu Desnoyers wrote:
> ----- On Jul 3, 2018, at 2:11 PM, Peter Zijlstra peterz@xxxxxxxxxxxxx wrote:
>
> > On Tue, Jul 03, 2018 at 01:58:37PM -0400, Mathieu Desnoyers wrote:
> >> I can modify the ABI to put the cpu_id_start and cpu_id fields inside
> >> a union, and update it with a single store.
> >>
> >> Thoughts ?
> >
> > Let's keep them for now, we can always frob this later, they are aligned
> > and proper, no need to expose that union to userspace.
>
> Isn't it weird to change the API of an exposed public uapi header ?
Sure, just keep it as is. We don't need an exposed union to do a single
store there.
Something like the ugly below preserves API but still does a single
store.
But sure, if you want to expose that union for some reason, then now is
the time.
diff --git a/kernel/rseq.c b/kernel/rseq.c
index 22b6acf1ad63..e956c48b5f83 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -85,10 +85,17 @@ static int rseq_update_cpu_id(struct task_struct *t)
{
u32 cpu_id = raw_smp_processor_id();
- if (__put_user(cpu_id, &t->rseq->cpu_id_start))
- return -EFAULT;
- if (__put_user(cpu_id, &t->rseq->cpu_id))
+ union {
+ struct {
+ u32 cpu_id_start;
+ u32 cpu_id;
+ };
+ u64 val;
+ } x = { { .cpu_id_start = cpu_id, .cpu_id = cpu_id, } };
+
+ if (__put_user(x.val, (u64 *)&t->rseq->cpu_id_start))
return -EFAULT;
+
trace_rseq_update(t);
return 0;
}
--
To unsubscribe from this list: send the line "unsubscribe linux-api" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
