Subject: Re: [PATCH 03/12] powerpc: qspinlock: Enforce qnode writes prior to publishing to queue

From: "Nicholas Piggin" <[email-masked]>
Date: Tue, 09 May 2023 12:04:42 +1000

On Mon May 8, 2023 at 12:01 PM AEST, Rohan McLure wrote:
> Use a compiler barrier to enforce that all fields of a new struct qnode
> be written to (especially the lock value) before publishing the qnode to
> the waitqueue.

publish_tail_cpu is the release barrier for this and includes the memory
clobber there. Can we annotate that instead?

Thanks,
Nick

>
> Signed-off-by: Rohan McLure <[email-masked]>
> ---
>  arch/powerpc/lib/qspinlock.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/arch/powerpc/lib/qspinlock.c b/arch/powerpc/lib/qspinlock.c
> index 579290d55abf..d548001a86be 100644
> --- a/arch/powerpc/lib/qspinlock.c
> +++ b/arch/powerpc/lib/qspinlock.c
> @@ -567,6 +567,10 @@ static __always_inline void queued_spin_lock_mcs_queue(struct qspinlock *lock, b
>  	node->cpu = smp_processor_id();
>  	node->yield_cpu = -1;
>  	node->locked = 1;
> +	/*
> +	 * Assign all attributes of a node before it can be published.
> +	 */
> +	barrier();
>  
>  	tail = encode_tail_cpu(node->cpu);
>  
> -- 
> 2.37.2