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Date: Wed, 18 Jul 2012 00:45:42 +0900
Message-ID: <CAAmzW4N+CJGnn3a6PUQZAeEeb4njp_zwXMhOSdSrHc36OLsDjg@mail.gmail.com>
Subject: Re: [PATCH 3/4 v2] mm: fix return value in __alloc_contig_migrate_range()
From: JoonSoo Kim <js1304@gmail.com>
To: Michal Nazarewicz <mina86@mina86.com>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Marek Szyprowski <m.szyprowski@samsung.com>,
        Minchan Kim <minchan@kernel.org>, Christoph Lameter <cl@linux.com>
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2012/7/17 Michal Nazarewicz <mina86@mina86.com>:
> On Tue, 17 Jul 2012 14:33:34 +0200, Joonsoo Kim <js1304@gmail.com> wrote:
>>
>> migrate_pages() would return positive value in some failure case,
>> so 'ret > 0 ? 0 : ret' may be wrong.
>> This fix it and remove one dead statement.
>
>
> How about the following message:
>
> ------------------- >8 ---------------------------------------------------
> migrate_pages() can return positive value while at the same time emptying
> the list of pages it was called with.  Such situation means that it went
> through all the pages on the list some of which failed to be migrated.
>
> If that happens, __alloc_contig_migrate_range()'s loop may finish without
> "++tries == 5" never being checked.  This in turn means that at the end
> of the function, ret may have a positive value, which should be treated
> as an error.
>
> This patch changes __alloc_contig_migrate_range() so that the return
> statement converts positive ret value into -EBUSY error.
> ------------------- >8 ---------------------------------------------------

It's good.
I will resend patch replacing my comment with yours.
Thanks for help.