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SubjectRe: mm: move_pages syscall can't return ENOENT when pages are not present
On 05/09/2012 05:28 PM, Xiaotian Feng wrote:

> On Wed, May 9, 2012 at 4:58 PM, Zhouping Liu <zliu@redhat.com> wrote:
>> 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.
>>
>> I have tested it on the latest kernel 3.4-rc5 with 2 and 4 numa nodes.
>> [zliu@ZhoupingLiu ~]$ gcc -o reproducer reproducer.c -lnuma
>> [zliu@ZhoupingLiu ~]$ ./reproducer
>> from_node is 1, to_node is 0
>> ERROR: move_pages expected FAIL.
>>
>
> " If nodes is not NULL, move_pages returns the number of valid
> migration requests which could not currently be performed. Otherwise
> it returns 0."


FYI, actually,
commit e78bbfa8262424417a29349a8064a535053912b9
Author: Brice Goglin <Brice.Goglin@inria.fr>
Date: Sat Oct 18 20:27:15 2008 -0700

mm: stop returning -ENOENT from sys_move_pages() if nothing got migrated

this commit changed the behaviour.

And the LTP has fixed to be consistent with this,
https://github.com/linux-test-project/ltp/commit/338299da1ff27c7815183c1b07eb91e705f117ce


Thanks,
Wanlong Gao

>
>> I'm not in mail list, please CC me.
>>
>> /*
>> * Copyright (C) 2012 Red Hat, Inc.
>> *
>> * This work is licensed under the terms of the GNU GPL, version 2. See
>> * the COPYING file in the top-level directory.
>> *
>> * Compiled: gcc -o reproducer reproducer.c -lnuma
>> * Description:
>> * it's designed to check move_pages syscall, when
>> * page is not present, it should fail with ENOENT.
>> */
>>
>> #include <sys/mman.h>
>> #include <sys/types.h>
>> #include <sys/wait.h>
>> #include <stdio.h>
>> #include <unistd.h>
>> #include <errno.h>
>> #include <numa.h>
>> #include <numaif.h>
>>
>> #define TEST_PAGES 4
>>
>> int main(int argc, char **argv)
>> {
>> void *pages[TEST_PAGES];
>> int onepage;
>> int nodes[TEST_PAGES];
>> int status, ret;
>> int i, from_node = 1, to_node = 0;
>>
>> onepage = getpagesize();
>>
>> for (i = 0; i < TEST_PAGES - 1; i++) {
>> pages[i] = numa_alloc_onnode(onepage, from_node);
>> nodes[i] = to_node;
>> }
>>
>> nodes[TEST_PAGES - 1] = to_node;
>>
>> /*
>> * the follow page is not available, also not aligned,
>> * depend on move_pages(2), it can't be moved, and should
>> * return ENOENT errno.
>> */
>> pages[TEST_PAGES - 1] = pages[TEST_PAGES - 2] - onepage * 4 + 1;
>>
>> printf("from_node is %u, to_node is %u\n", from_node, to_node);
>> ret = move_pages(0, TEST_PAGES, pages, nodes, &status, MPOL_MF_MOVE);
>> if (ret == -1) {
>> if (errno != ENOENT)
>> perror("move_pages expected ENOENT errno, but it's");
>> else
>> printf("Succeed\n");
>> } else {
>> printf("ERROR: move_pages expected FAIL.\n");
>> }
>>
>> for (i = 0; i < TEST_PAGES; i++)
>> numa_free(pages[i], onepage);
>>
>> return 0;
>> }
>>
>> --
>> Thanks,
>> Zhouping
>> --
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