linux-kernel - Re: [PATCH v2] mm/swapfile.c: simplify the scan loop in scan_swap_map

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Sun, 26 Apr 2020 09:07:11 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v2] mm/swapfile.c: simplify the scan loop in scan_swap_map_slots()

Wei Yang <richard.weiyang@...il.com> writes:

> On Fri, Apr 24, 2020 at 10:02:58AM +0800, Huang, Ying wrote:
>>Wei Yang <richard.weiyang@...il.com> writes:
>>
> [...]
>>>>
>>>>if "offset > si->highest_bit" is true and "offset < scan_base" is true,
>>>>scan_base need to be returned.
>>>>
>>>
>>> When this case would happen in the original code?
>>
>>In the original code, the loop can still stop.
>>
>
> Sorry, I don't get your point yet.
>
> In original code, there are two separate loops
>
>     while (++offset <= si->highest_bit) {
>     }
>
>     while (offset < scan_base) {
>     }
>
> And for your condition, (offset > highest_bit) && (offset < scan_base), which
> terminates the first loop and fits the second loop well.
>
> Not sure how this condition would stop the loop in original code?

Per my understanding, in your code, if some other task changes
si->highest_bit to be less than scan_base in parallel.  The loop may
cannot stop.

Best Regards,
Huang, Ying

>>Best Regards,
>>Huang, Ying
>>
>>>>Again, the new code doesn't make it easier to find this kind of issues.
>>>>
>>>>Best Regards,
>>>>Huang, Ying