linux-kernel - Re: [PATCH v18 05/10] xbitmap: add more operations

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Message-Id: <201712031050.IAC64520.QVLFFOOJOSFtHM@I-love.SAKURA.ne.jp>
Date:   Sun, 3 Dec 2017 10:50:42 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     willy@...radead.org, wei.w.wang@...el.com
Cc:     virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org,
        qemu-devel@...gnu.org, virtualization@...ts.linux-foundation.org,
        kvm@...r.kernel.org, linux-mm@...ck.org, mst@...hat.com,
        mhocko@...nel.org, akpm@...ux-foundation.org,
        mawilcox@...rosoft.com, david@...hat.com, cornelia.huck@...ibm.com,
        mgorman@...hsingularity.net, aarcange@...hat.com,
        amit.shah@...hat.com, pbonzini@...hat.com,
        liliang.opensource@...il.com, yang.zhang.wz@...il.com,
        quan.xu@...yun.com, nilal@...hat.com, riel@...hat.com
Subject: Re: [PATCH v18 05/10] xbitmap: add more operations

Matthew Wilcox wrote:
> On Fri, Dec 01, 2017 at 03:09:08PM +0000, Wang, Wei W wrote:
> > On Friday, December 1, 2017 9:02 PM, Tetsuo Handa wrote:
> > > If start == end is legal,
> > > 
> > >    for (; start < end; start = (start | (IDA_BITMAP_BITS - 1)) + 1) {
> > > 
> > > makes this loop do nothing because 10 < 10 is false.
> > 
> > How about "start <= end "?
> 
> Don't ask Tetsuo for his opinion, write some userspace code that uses it.
> 

Please be sure to prepare for "end == -1UL" case, for "start < end" will become
true when "start = (start | (IDA_BITMAP_BITS - 1)) + 1" made "start == 0" due to
overflow.