Re: [PATCH v2 4/6] locking/lockdep: Reuse freed chain_hlocks entries

[Peter Zijlstra]

On Mon, Dec 16, 2019 at 10:15:15AM -0500, Waiman Long wrote:
> +#define CHAIN_HLOCKS_MASK	0xffff

> +static inline void set_chain_block(int offset, int size, int next)
> +{
> +	if (unlikely(offset < 0)) {
> +		chain_block_buckets[0] = next;
> +		return;
> +	}
> +	chain_hlocks[offset] = (next >> 16) | CHAIN_BLK_FLAG;
> +	chain_hlocks[offset + 1] = next & CHAIN_HLOCKS_MASK;
> +	if (size > MAX_CHAIN_BUCKETS) {
> +		chain_hlocks[offset + 2] = size >> 16;
> +		chain_hlocks[offset + 3] = size & CHAIN_HLOCKS_MASK;
> +	}
> +}

AFAICT HLOCKS_MASK is superfluous. That is, you're assigning to a u16,
it will truncate automagically.

But if you want to make it more explicit, something like:

  chain_hlocks[offset + 1] = (u16)next;

might be easier to read still.