Re: [PATCH 2/3] KVM: Use atomic_long_cmpxchg() instead of an open-coded variant

[Paolo Bonzini]

On 11/26/21 01:31, Maciej S. Szmigiero wrote:
> -		if ((long)old == atomic_long_read(&slots->last_used_slot))
> -			atomic_long_set(&slots->last_used_slot, (long)new);
> +		/*
> +		 * The atomicity isn't strictly required here since we are
> +		 * operating on an inactive memslots set anyway.
> +		 */
> +		atomic_long_cmpxchg(&slots->last_used_slot,
> +				    (unsigned long)old, (unsigned long)new);

I think using read/set is more readable than a comment saying that 
atomicity is not required.

It's a fairly common pattern, and while I agree that it's a PITA to 
write atomic_long_read and atomic_long_set, the person that reads the 
code is also helped by read/set, because they know they have to think 
about ownership invariants rather than concurrency invariants.

Paolo