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

Thomas Gleixner
2023-05-09T20:11:10Z

On Tue, May 09 2023 at 12:04, Peter Zijlstra wrote:
> On Mon, May 08, 2023 at 09:43:39PM +0200, Thomas Gleixner wrote:
> Not to the detriment of this patch, but this barrier() and it's comment
> seem weird vs smp_callin(). That function ends with an atomic bitop (it
> has to, at the very least it must not be weaker than store-release) but
> also has an explicit wmb() to order setup vs CPU_STARTING.
>
> (arguably that should be a full fence *AND* get a comment)

TBH: I'm grasping for something 'arguable': What's the point of this
wmb() or even a mb()?

Most of the [w]mb()'s in smpboot.c except those in mwait_play_dead()
have a very distinct voodoo programming smell.

Thanks,

tglx