Re: [PATCH v2 4/5] proc/task_mmu: read proc/pid/smaps_rollup under per-vma lock

[David Hildenbrand (Arm)]

> -	vma_start = vma->vm_start;
> -	do {
> -		smap_gather_stats(priv, vma, &mss, vma->vm_start);
> -		last_vma_end = vma->vm_end;
> +	if (!IS_ERR(vma) && vma != get_gate_vma(lock_ctx->mm))
> +		vma_start = vma->vm_start;
> +
> +	while (vma) {
> +		if (IS_ERR(vma)) {
> +			ret = PTR_ERR(vma);
> +			goto out_unlock;
> +		}
> +

Can we add a comment whey we break (and not e.g., continue) whenw e hit the gate
VMA?

(I seriously don't kmow ... should I know? :) )

> +		if (vma == get_gate_vma(lock_ctx->mm))
> +			break;
>  
>  		/*
> -		 * Release mmap_lock temporarily if someone wants to
> -		 * access it for write request.
> +		 * If after retaking the lock, already reported VMA grew or
> +		 * merged with the next one, smap_gather_stats() will gather
> +		 * stats for the remaining portion by starting at last_vma_end.
>  		 */
> -		if (mmap_lock_is_contended(mm)) {
> -			vma_iter_invalidate(&vmi);
> -			unlock_ctx_mm(&priv->lock_ctx);
> -			ret = lock_ctx_mm(&priv->lock_ctx);
> -			if (ret) {
> -				release_task_mempolicy(priv);
> -				goto out_put_mm;
> -			}
> +		smap_gather_stats(priv, vma, &mss, last_vma_end);
> +		last_vma_end = vma->vm_end;

I skimmed over the remaining bits, hoping the VMA lock experts will review in
detail :)

-- 
Cheers,

David