Re: [patch v3 08/36] x86/smpboot: Split up native_cpu_up() into separate phases and document them

Thomas Gleixner
2023-05-09T18:03:37Z

On Tue, May 09 2023 at 12:19, Peter Zijlstra wrote:
> Again, not really this patch, but since I had to look at this code ....
>
> On Mon, May 08, 2023 at 09:43:39PM +0200, Thomas Gleixner wrote:
>> @@ -1048,60 +1066,89 @@ static int do_boot_cpu(int apicid, int c
>
> /*
> * AP might wait on cpu_callout_mask in cpu_init() with
> * cpu_initialized_mask set if previous attempt to online
> * it timed-out. Clear cpu_initialized_mask so that after
> * INIT/SIPI it could start with a clean state.
> */
> cpumask_clear_cpu(cpu, cpu_initialized_mask);
> smp_mb();
>
> ^^^ that barrier is weird too, cpumask_clear_cpu() is an atomic op and
> implies much the same (this is x86 after all). If you want to be super
> explicit about it write:
>
> smp_mb__after_atomic();
>
> (which is a no-op) but then it still very much requires a comment as to
> what exactly it orders against what.

Won't bother either as that mask is gone a few patches later.