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Re: [patch v3 18/36] [patch V2 18/38] cpu/hotplug: Add CPU state tracking and synchronization
- To: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
- From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- Date: Tue, 9 May 2023 13:35:48 +0200
- Cc: LKML <linux-kernel@xxxxxxxxxxxxxxx>, x86@xxxxxxxxxx, David Woodhouse <dwmw2@xxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Brian Gerst <brgerst@xxxxxxxxx>, Arjan van de Veen <arjan@xxxxxxxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Paul McKenney <paulmck@xxxxxxxxxx>, Tom Lendacky <thomas.lendacky@xxxxxxx>, Sean Christopherson <seanjc@xxxxxxxxxx>, Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>, Paul Menzel <pmenzel@xxxxxxxxxxxxx>, "Guilherme G. Piccoli" <gpiccoli@xxxxxxxxxx>, Piotr Gorski <lucjan.lucjanov@xxxxxxxxx>, Usama Arif <usama.arif@xxxxxxxxxxxxx>, Juergen Gross <jgross@xxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Russell King <linux@xxxxxxxxxxxxxxx>, Arnd Bergmann <arnd@xxxxxxxx>, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx, Catalin Marinas <catalin.marinas@xxxxxxx>, Will Deacon <will@xxxxxxxxxx>, Guo Ren <guoren@xxxxxxxxxx>, linux-csky@xxxxxxxxxxxxxxx, Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>, linux-mips@xxxxxxxxxxxxxxx, "James E.J. Bottomley" <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx>, Helge Deller <deller@xxxxxx>, linux-parisc@xxxxxxxxxxxxxxx, Paul Walmsley <paul.walmsley@xxxxxxxxxx>, Palmer Dabbelt <palmer@xxxxxxxxxxx>, linux-riscv@xxxxxxxxxxxxxxxxxxx, Mark Rutland <mark.rutland@xxxxxxx>, Sabin Rapan <sabrapan@xxxxxxxxxx>, "Michael Kelley (LINUX)" <mikelley@xxxxxxxxxxxxx>
- Delivery-date: Tue, 09 May 2023 11:36:50 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Tue, May 09, 2023 at 01:07:23PM +0200, Peter Zijlstra wrote:
> On Mon, May 08, 2023 at 09:43:55PM +0200, Thomas Gleixner wrote:
>
> > +static inline void cpuhp_ap_update_sync_state(enum cpuhp_sync_state state)
> > +{
> > + atomic_t *st = this_cpu_ptr(&cpuhp_state.ap_sync_state);
> > + int sync = atomic_read(st);
> > +
> > + while (!atomic_try_cmpxchg(st, &sync, state));
> > +}
>
> Why isn't:
>
> atomic_set(st, state);
>
> any good?
Hmm, should at the very least be atomic_set_release(), but if you want
the full barrier then:
(void)atomic_xchg(st, state);
is the much saner way to write the above.
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