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Date: Mon, 17 Oct 2016 20:48:15 +0800
From: zhong jiang <zhongjiang@huawei.com>
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To: Vitaly Wool <vitalywool@gmail.com>
CC: Dave Chinner <david@fromorbit.com>,
        Seth Jennings <sjenning@redhat.com>, Dan Streetman <ddstreet@ieee.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@kernel.org>, Vlastimil Babka <vbabka@suse.cz>,
        LKML <linux-kernel@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH v2] z3fold: fix the potential encode bug in encod_handle
References: <1476331337-17253-1-git-send-email-zhongjiang@huawei.com> <5804305F.4030302@huawei.com> <CAMJBoFMcnH3ZPQpG=oAjD=K64O7MX_BdFvHvccvgCV4nFSfxXA@mail.gmail.com>
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On 2016/10/17 20:03, Vitaly Wool wrote:
> Hi Zhong Jiang,
>
> On Mon, Oct 17, 2016 at 3:58 AM, zhong jiang <zhongjiang@huawei.com> wrote:
>> Hi,  Vitaly
>>
>> About the following patch,  is it right?
>>
>> Thanks
>> zhongjiang
>> On 2016/10/13 12:02, zhongjiang wrote:
>>> From: zhong jiang <zhongjiang@huawei.com>
>>>
>>> At present, zhdr->first_num plus bud can exceed the BUDDY_MASK
>>> in encode_handle, it will lead to the the caller handle_to_buddy
>>> return the error value.
>>>
>>> The patch fix the issue by changing the BUDDY_MASK to PAGE_MASK,
>>> it will be consistent with handle_to_z3fold_header. At the same time,
>>> change the BUDDY_MASK to PAGE_MASK in handle_to_buddy is better.
> are you seeing problems with the existing code? first_num should wrap around
> BUDDY_MASK and this should be ok because it is way bigger than the number
> of buddies.
>
> ~vitaly
>
> .
>
 first_num plus buddies can exceed the BUDDY_MASK. is it right?
 (first_num + buddies) & BUDDY_MASK may be a smaller value than first_num.

  but (handle - zhdr->first_num) & BUDDY_MASK will return incorrect value
  in handle_to_buddy.

  Thanks
  zhongjiang