From: David Stevens stevensd@chromium.org

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.

Fixes: b9a8a4195c7d ("truncate,shmem: Handle truncates that split large folios") Cc: stable@vger.kernel.org Signed-off-by: David Stevens stevensd@chromium.org --- v1 -> v2: - Actually drop pages after splitting a THP

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

diff --git a/mm/shmem.c b/mm/shmem.c index 9218c955f482..226c94a257b1 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1033,7 +1033,22 @@ static void shmem_undo_range(struct inode *inode, loff_t lstart, loff_t lend, } 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); }