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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 30.08.16 at 01:19, <feng.wu@xxxxxxxxx> wrote:
>> From: Jan Beulich [mailto:JBeulich@xxxxxxxx]
>> Sent: Monday, August 29, 2016 7:51 PM
>> >>> On 29.08.16 at 11:14, <feng.wu@xxxxxxxxx> 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];
> 
> Thanks for the comments, both are good to me, but I slightly prefer this
> one. Do I need to send another version?

Not necessarily - can you reason a little about your preference? I
particularly dislike the subtraction necessary here:

          dest = d->vcpu[idx - 1];

Jan


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