The patch titled Subject: mm/shmem: fix THP allocation and fallback loop has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-shmem-fix-thp-allocation-and-fallback-loop.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Kairui Song kasong@tencent.com Subject: mm/shmem: fix THP allocation and fallback loop Date: Wed, 22 Oct 2025 18:57:19 +0800

The order check and fallback loop is updating the index value on every loop, this will cause the index to be aligned by a larger value while the loop shrinks the order.

This may result in inserting and returning a folio of the wrong index and cause data corruption with some userspace workloads [1].

Link: https://lkml.kernel.org/r/20251022105719.18321-1-ryncsn@gmail.com Link: https://lore.kernel.org/linux-mm/CAMgjq7DqgAmj25nDUwwu1U2cSGSn8n4-Hqpgottedy... [1] Fixes: e7a2ab7b3bb5d ("mm: shmem: add mTHP support for anonymous shmem") Signed-off-by: Kairui Song kasong@tencent.com Cc: Baolin Wang baolin.wang@linux.alibaba.com Cc: Barry Song baohua@kernel.org Cc: David Hildenbrand david@redhat.com Cc: Dev Jain dev.jain@arm.com Cc: Hugh Dickins hughd@google.com Cc: Liam Howlett liam.howlett@oracle.com Cc: Lorenzo Stoakes lorenzo.stoakes@oracle.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Nico Pache npache@redhat.com 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/shmem.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/mm/shmem.c~mm-shmem-fix-thp-allocation-and-fallback-loop +++ a/mm/shmem.c @@ -1895,10 +1895,11 @@ static struct folio *shmem_alloc_and_add order = highest_order(suitable_orders); while (suitable_orders) { pages = 1UL << order; - index = round_down(index, pages); - folio = shmem_alloc_folio(gfp, order, info, index); - if (folio) + folio = shmem_alloc_folio(gfp, order, info, round_down(index, pages)); + if (folio) { + index = round_down(index, pages); goto allocated; + }

if (pages == HPAGE_PMD_NR) count_vm_event(THP_FILE_FALLBACK); _

Patches currently in -mm which might be from kasong@tencent.com are

mm-shmem-fix-thp-allocation-and-fallback-loop.patch