linux-kernel - Re: mm: move_pages syscall can't return ENOENT when pages are not present

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Message-ID: <4FAA7A51.6050504@inria.fr>
Date:	Wed, 09 May 2012 16:08:17 +0200
From:	Brice Goglin <Brice.Goglin@...ia.fr>
To:	Zhouping Liu <zliu@...hat.com>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: mm: move_pages syscall can't return ENOENT when pages are not
 present

Le 09/05/2012 10:58, Zhouping Liu a écrit :
> hi, all
>
> Recently, I found an error in move_pages syscall:
>
> depending on move_pages(2), when page is not present,
> it should fail with ENOENT, in fact, it's ok without
> any errno.
>
> the following reproducer can easily reproduce
> the issue, suggest you get more details by strace.
> inside reproducer, I try to move a non-exist page from
> node 1 to node 0.
>

If I understand correctly, 3 pages should migrate properly but the last
one cannot migrate because it's not present. In this case, move_pages
returns success. -ENOENT is set in the status array, not in the return
value/errno.

In the past, if *all* pages failed to migrate, move_pages would return
ENOENT instead of success, but the behavior was inconsistent so I
changed that in commit e78bbfa8262424417a29349a8064a535053912b9 as
Wanlong Gao said. But that should not matter here since 3 pages out of 4
are successfully migrated from what I understand.

The manpage should be updated (remove ENOENT from the ERRORS section,
but keep it in the "Page states in the status array" section).

Brice

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