Re: [PATCH] idr: fix backtrack logic in idr_remove_all

[Tejun Heo <tj@kernel.org>]

On 05/18/2010 01:18 PM, Imre Deak wrote:
>> Shouldn't this be id ^ bt_mask?  The above only detects 1 -> 0
>> transitions not the other way around.
> 
> It works according to the following with n=1:
> 
> id            id+2            fls((id+2) & ~id)
> 0             2               2
> 2             4               3
> 4             6               2
> 6             8               4
> 8             10              2
> 10            12              3
> 12            14              2
> 
> I think this should work.

Ah, I thought you were doing fls(id & ~(id + 2)) and thus looking at 1
-> 0 transitions.  It's the other way and you're looking for the
highest 0 -> 1 transition which should be the same to the highest bit
changing if you aren't overflowing.  The patch looks good then.  I
still think ^ test would be clearer tho.  Hmmm... Can you please add
little comment there stating that you're looking for the highest bit
flipping?

Reviewed-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun