* + mm-migrate-fix-shmem-xarray-update-during-migration.patch added to mm-hotfixes-unstable branch
@ 2025-03-04 2:59 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2025-03-04 2:59 UTC (permalink / raw)
To: mm-commits, willy, wangkefeng.wang, stable, shivankg,
ryan.roberts, quic_charante, liushixin2, ioworker0, hughd, david,
baolin.wang, baohua, ziy, akpm
The patch titled
Subject: mm/migrate: fix shmem xarray update during migration
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-migrate-fix-shmem-xarray-update-during-migration.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-migrate-fix-shmem-xarray-update-during-migration.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Zi Yan <ziy@nvidia.com>
Subject: mm/migrate: fix shmem xarray update during migration
Date: Fri, 28 Feb 2025 12:49:53 -0500
Pagecache uses multi-index entries for large folio, so does shmem. Only
swap cache still stores multiple entries for a single large folio. Commit
fc346d0a70a1 ("mm: migrate high-order folios in swap cache correctly")
fixed swap cache but got shmem wrong by storing multiple entries for a
large shmem folio.
This results in a soft lockup as reported by Liu Shixin.
Fix it by storing a single entry for a shmem folio.
Link: https://lkml.kernel.org/r/20250228174953.2222831-1-ziy@nvidia.com
Fixes: fc346d0a70a1 ("mm: migrate high-order folios in swap cache correctly")
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reported-by: Liu Shixin <liushixin2@huawei.com>
Closes: https://lore.kernel.org/all/28546fb4-5210-bf75-16d6-43e1f8646080@huawei.com/
Reviewed-by: Shivank Garg <shivankg@amd.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Charan Teja Kalla <quic_charante@quicinc.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickens <hughd@google.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/migrate.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
--- a/mm/migrate.c~mm-migrate-fix-shmem-xarray-update-during-migration
+++ a/mm/migrate.c
@@ -524,7 +524,11 @@ static int __folio_migrate_mapping(struc
folio_set_swapcache(newfolio);
newfolio->private = folio_get_private(folio);
}
- entries = nr;
+ /* shmem uses high-order entry */
+ if (!folio_test_anon(folio))
+ entries = 1;
+ else
+ entries = nr;
} else {
VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio);
entries = 1;
_
Patches currently in -mm which might be from ziy@nvidia.com are
mm-migrate-fix-shmem-xarray-update-during-migration.patch
selftests-mm-make-file-backed-thp-split-work-by-writing-pmd-size-data.patch
mm-huge_memory-allow-split-shmem-large-folio-to-any-lower-order.patch
selftests-mm-test-splitting-file-backed-thp-to-any-lower-order.patch
xarray-add-xas_try_split-to-split-a-multi-index-entry.patch
mm-huge_memory-add-two-new-not-yet-used-functions-for-folio_split.patch
mm-huge_memory-move-folio-split-common-code-to-__folio_split.patch
mm-huge_memory-add-buddy-allocator-like-non-uniform-folio_split.patch
mm-huge_memory-remove-the-old-unused-__split_huge_page.patch
mm-huge_memory-add-folio_split-to-debugfs-testing-interface.patch
mm-truncate-use-buddy-allocator-like-folio-split-for-truncate-operation.patch
mm-truncate-use-buddy-allocator-like-folio-split-for-truncate-operation-fix.patch
selftests-mm-add-tests-for-folio_split-buddy-allocator-like-split.patch
mm-filemap-use-xas_try_split-in-__filemap_add_folio.patch
mm-shmem-use-xas_try_split-in-shmem_split_large_entry.patch
^ permalink raw reply [flat|nested] 2+ messages in thread* + mm-migrate-fix-shmem-xarray-update-during-migration.patch added to mm-hotfixes-unstable branch
@ 2025-03-05 21:42 Andrew Morton
0 siblings, 0 replies; 2+ messages in thread
From: Andrew Morton @ 2025-03-05 21:42 UTC (permalink / raw)
To: mm-commits, willy, wangkefeng.wang, stable, ryan.roberts,
quic_charante, liushixin2, ioworker0, hughd, david, baolin.wang,
baohua, ziy, akpm
The patch titled
Subject: mm/migrate: fix shmem xarray update during migration
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-migrate-fix-shmem-xarray-update-during-migration.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-migrate-fix-shmem-xarray-update-during-migration.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Zi Yan <ziy@nvidia.com>
Subject: mm/migrate: fix shmem xarray update during migration
Date: Wed, 5 Mar 2025 15:04:03 -0500
A shmem folio can be either in page cache or in swap cache, but not at the
same time. Namely, once it is in swap cache, folio->mapping should be
NULL, and the folio is no longer in a shmem mapping.
In __folio_migrate_mapping(), to determine the number of xarray entries to
update, folio_test_swapbacked() is used, but that conflates shmem in page
cache case and shmem in swap cache case. It leads to xarray multi-index
entry corruption, since it turns a sibling entry to a normal entry during
xas_store() (see [1] for a userspace reproduction). Fix it by only using
folio_test_swapcache() to determine whether xarray is storing swap cache
entries or not to choose the right number of xarray entries to update.
[1] https://lore.kernel.org/linux-mm/Z8idPCkaJW1IChjT@casper.infradead.org/
Note:
In __split_huge_page(), folio_test_anon() && folio_test_swapcache() is
used to get swap_cache address space, but that ignores the shmem folio in
swap cache case. It could lead to NULL pointer dereferencing when a
in-swap-cache shmem folio is split at __xa_store(), since
!folio_test_anon() is true and folio->mapping is NULL. But fortunately,
its caller split_huge_page_to_list_to_order() bails out early with EBUSY
when folio->mapping is NULL. So no need to take care of it here.
Link: https://lkml.kernel.org/r/20250305200403.2822855-1-ziy@nvidia.com
Fixes: fc346d0a70a1 ("mm: migrate high-order folios in swap cache correctly")
Reported-by: Liu Shixin <liushixin2@huawei.com>
Closes: https://lore.kernel.org/all/28546fb4-5210-bf75-16d6-43e1f8646080@huawei.com/
Suggested-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Charan Teja Kalla <quic_charante@quicinc.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Matthew Wilcow (Oracle) <willy@infradead.org>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/migrate.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)
--- a/mm/migrate.c~mm-migrate-fix-shmem-xarray-update-during-migration
+++ a/mm/migrate.c
@@ -518,15 +518,13 @@ static int __folio_migrate_mapping(struc
if (folio_test_anon(folio) && folio_test_large(folio))
mod_mthp_stat(folio_order(folio), MTHP_STAT_NR_ANON, 1);
folio_ref_add(newfolio, nr); /* add cache reference */
- if (folio_test_swapbacked(folio)) {
+ if (folio_test_swapbacked(folio))
__folio_set_swapbacked(newfolio);
- if (folio_test_swapcache(folio)) {
- folio_set_swapcache(newfolio);
- newfolio->private = folio_get_private(folio);
- }
+ if (folio_test_swapcache(folio)) {
+ folio_set_swapcache(newfolio);
+ newfolio->private = folio_get_private(folio);
entries = nr;
} else {
- VM_BUG_ON_FOLIO(folio_test_swapcache(folio), folio);
entries = 1;
}
_
Patches currently in -mm which might be from ziy@nvidia.com are
mm-migrate-fix-shmem-xarray-update-during-migration.patch
selftests-mm-make-file-backed-thp-split-work-by-writing-pmd-size-data.patch
mm-huge_memory-allow-split-shmem-large-folio-to-any-lower-order.patch
selftests-mm-test-splitting-file-backed-thp-to-any-lower-order.patch
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