Re: [PATCH -V3 1/8] migrate: fix syscall move_pages() return value for failure

[Ryan Roberts <ryan.roberts@arm.com>]

On 17/08/2022 09:14, Huang Ying wrote:
> The return value of move_pages() syscall is incorrect when counting
> the remaining pages to be migrated.

Hi Huang, Alistair,

I've noticed that this patch from Huang has caused the mm/migration selftest (authored by Alistair) to start failing (see bisection log below).

Of the 3 tests, migration.private_anon and migration.private_anon_thp continue to pass, but migration.shared_anon fails:


  #  RUN           migration.shared_anon ...
  Didn't migrate 1 pages
  # migration.c:167:shared_anon:Expected migrate(ptr, self->n1, self->n2) (-2) == 0 (0)
  # shared_anon: Test terminated by assertion
  #          FAIL  migration.shared_anon
  not ok 2 migration.shared_anon


The failure occurs due to the return code of move_pages() and this patch has changed the return code handling in the kernel, so it makes sense:


int migrate(uint64_t *ptr, int n1, int n2)
{
	int ret, tmp;
	int status = 0;
	struct timespec ts1, ts2;

	if (clock_gettime(CLOCK_MONOTONIC, &ts1))
		return -1;

	while (1) {
		if (clock_gettime(CLOCK_MONOTONIC, &ts2))
			return -1;

		if (ts2.tv_sec - ts1.tv_sec >= RUNTIME)
			return 0;

		ret = move_pages(0, 1, (void **) &ptr, &n2, &status,
				MPOL_MF_MOVE_ALL);
		if (ret) {
			if (ret > 0)
				printf("Didn't migrate %d pages\n", ret); <<<< HERE
			else
				perror("Couldn't migrate pages");
			return -2;
		}

		tmp = n2;
		n2 = n1;
		n1 = tmp;
	}

	return 0;
}


I haven't looked any further and am not sure what the correct fix is. I wondered if either you might be able to offer a solution?

Thanks,
Ryan


git bisect start
# bad: [6eaae198076080886b9e7d57f4ae06fa782f90ef] Linux 6.5-rc3
git bisect bad 6eaae198076080886b9e7d57f4ae06fa782f90ef
# good: [2c85ebc57b3e1817b6ce1a6b703928e113a90442] Linux 5.10
git bisect good 2c85ebc57b3e1817b6ce1a6b703928e113a90442
# good: [d710d370c4911e83da5d2bc43d4a2c3b56bd27e7] Merge tag 's390-5.18-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux
git bisect good d710d370c4911e83da5d2bc43d4a2c3b56bd27e7
# bad: [8715c6d3100fc7c6edddf29af4a399a1c12d028c] Merge tag 'for-6.2/dm-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm
git bisect bad 8715c6d3100fc7c6edddf29af4a399a1c12d028c
# good: [12b68040a5e468068fd7f4af1150eab8f6e96235] Merge tag 'media/v5.20-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media
git bisect good 12b68040a5e468068fd7f4af1150eab8f6e96235
# good: [7e6739b9336e61fe23ca4e2c8d1fda8f19f979bf] Merge tag 'drm-next-2022-10-05' of git://anongit.freedesktop.org/drm/drm
git bisect good 7e6739b9336e61fe23ca4e2c8d1fda8f19f979bf
# bad: [524d0c68826bc1adf9d1946e540eb4f7b16699a7] Merge tag 'ceph-for-6.1-rc1' of https://github.com/ceph/ceph-client
git bisect bad 524d0c68826bc1adf9d1946e540eb4f7b16699a7
# good: [29926f1cd3535f565f200430d5b6a794543fe130] fbdev: mb862xx: Fix check of return value from irq_of_parse_and_map()
git bisect good 29926f1cd3535f565f200430d5b6a794543fe130
# good: [d4013bc4d49f6da8178a340348369bb9920225c9] Merge tag 'bitmap-6.1-rc1' of https://github.com/norov/linux
git bisect good d4013bc4d49f6da8178a340348369bb9920225c9
# bad: [ac1e8c6c95bf805c699656046aef0a05205edfbd] Merge tag '6.1-rc-smb3-client-fixes-part1' of git://git.samba.org/sfrench/cifs-2.6
git bisect bad ac1e8c6c95bf805c699656046aef0a05205edfbd
# bad: [f80be4571b19b9fd8dd1528cd2a2f123aff51f70] kmsan: add KMSAN runtime core
git bisect bad f80be4571b19b9fd8dd1528cd2a2f123aff51f70
# bad: [c4c84f06285e48f80e9843d0775ad92714ffc35a] fs/proc/task_mmu: stop using linked list and highest_vm_end
git bisect bad c4c84f06285e48f80e9843d0775ad92714ffc35a
# good: [8c004d1fc1497d9a6d92ea968bd58230af59a492] jbd2: replace ll_rw_block()
git bisect good 8c004d1fc1497d9a6d92ea968bd58230af59a492
# bad: [f76c83378851f8e70f032848c4e61203f39480e4] mm: multi-gen LRU: optimize multiple memcgs
git bisect bad f76c83378851f8e70f032848c4e61203f39480e4
# good: [36537a67d3561bfe2b3654161d6c9008fff84d43] mm, hwpoison: avoid unneeded page_mapped_in_vma() overhead in collect_procs_anon()
git bisect good 36537a67d3561bfe2b3654161d6c9008fff84d43
# bad: [5fc30916b5cda697a7eb8f1167c38c27100a793a] migrate_pages(): fix failure counting for THP subpages retrying
git bisect bad 5fc30916b5cda697a7eb8f1167c38c27100a793a
# good: [2e3468778dbe3ec389a10c21a703bb8e5be5cfbc] mm: remember young/dirty bit for page migrations
git bisect good 2e3468778dbe3ec389a10c21a703bb8e5be5cfbc
# good: [f347c9d2697fcbbb64e077f7113a3887a181b8c0] filemap: make the accounting of thrashing more consistent
git bisect good f347c9d2697fcbbb64e077f7113a3887a181b8c0
# bad: [9c62ff005fc774fb2ba14223b0d865a8aca48fb5] migrate_pages(): remove unnecessary list_safe_reset_next()
git bisect bad 9c62ff005fc774fb2ba14223b0d865a8aca48fb5
# bad: [a7504ed14f9b5e873599b2487eb95062dd0b65f8] migrate: fix syscall move_pages() return value for failure
git bisect bad a7504ed14f9b5e873599b2487eb95062dd0b65f8
# first bad commit: [a7504ed14f9b5e873599b2487eb95062dd0b65f8] migrate: fix syscall move_pages() return value for failure