Re: [Xen-devel] [PATCH] Fix a BUG_ON issue

[Jan Beulich]

>>> On 29.08.16 at 11:14, <feng...@intel.com> wrote:
> --- a/xen/drivers/passthrough/io.c
> +++ b/xen/drivers/passthrough/io.c
> @@ -243,7 +243,7 @@ static struct vcpu *vector_hashing_dest(const struct 
> domain *d,
>          for ( i = 0; i <= mod; i++ )
>          {
>              idx = find_next_bit(dest_vcpu_bitmap, d->max_vcpus, idx) + 1;
> -            BUG_ON(idx >= d->max_vcpus);
> +            BUG_ON(idx > d->max_vcpus);
>          }
>  
>          dest = d->vcpu[idx - 1];

Wouldn't it be better to change the code to

        unsigned int idx = -1;

        for ( i = 0; i <= mod; i++ )
        {
            idx = find_next_bit(dest_vcpu_bitmap, d->max_vcpus, idx + 1);
            BUG_ON(idx >= d->max_vcpus);
        }

        dest = d->vcpu[idx];

or, not utilizing wrapping

        unsigned int idx = find_first_bit(dest_vcpu_bitmap, d->max_vcpus);

        for ( i = 0; i < mod; i++ )
            idx = find_next_bit(dest_vcpu_bitmap, d->max_vcpus, idx + 1);

        BUG_ON(idx >= d->max_vcpus);

        dest = d->vcpu[idx];

Jan


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