The patch titled Subject: mm/shmem: Fix race in shmem_undo_range w/THP has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-shmem-fix-race-in-shmem_undo_range-w-thp.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: David Stevens stevensd@chromium.org Subject: mm/shmem: Fix race in shmem_undo_range w/THP Date: Tue, 18 Apr 2023 17:40:31 +0900

Split folios during the second loop of shmem_undo_range. It's not sufficient to only split folios when dealing with partial pages, since it's possible for a THP to be faulted in after that point. Calling truncate_inode_folio in that situation can result in throwing away data outside of the range being targeted.

Link: https://lkml.kernel.org/r/20230418084031.3439795-1-stevensd@google.com Fixes: b9a8a4195c7d ("truncate,shmem: Handle truncates that split large folios") Signed-off-by: David Stevens stevensd@chromium.org Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Suleiman Souhlal suleiman@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/shmem.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-)

--- a/mm/shmem.c~mm-shmem-fix-race-in-shmem_undo_range-w-thp +++ a/mm/shmem.c @@ -1022,7 +1022,22 @@ whole_folios: } VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio); - truncate_inode_folio(mapping, folio); + + if (!folio_test_large(folio)) { + truncate_inode_folio(mapping, folio); + } else if (truncate_inode_partial_folio(folio, lstart, lend)) { + /* + * If we split a page, reset the loop so that we + * pick up the new sub pages. Otherwise the THP + * was entirely dropped or the target range was + * zeroed, so just continue the loop as is. + */ + if (!folio_test_large(folio)) { + folio_unlock(folio); + index = start; + break; + } + } } folio_unlock(folio); } _

Patches currently in -mm which might be from stevensd@chromium.org are

mm-shmem-fix-race-in-shmem_undo_range-w-thp.patch mm-khugepaged-drain-lru-after-swapping-in-shmem.patch mm-khugepaged-refactor-collapse_file-control-flow.patch mm-khugepaged-skip-shmem-with-userfaultfd.patch mm-khugepaged-maintain-page-cache-uptodate-flag.patch