6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: David Stevens <stevensd@xxxxxxxxxxxx> commit 55ac8bbe358bdd2f3c044c12f249fd22d48fe015 upstream. 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. [akpm@xxxxxxxxxxxxxxxxxxxx: tidy up comment layout] Link: https://lkml.kernel.org/r/20230418084031.3439795-1-stevensd@xxxxxxxxxx Fixes: b9a8a4195c7d ("truncate,shmem: Handle truncates that split large folios") Signed-off-by: David Stevens <stevensd@xxxxxxxxxxxx> Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Cc: Suleiman Souhlal <suleiman@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/shmem.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1024,7 +1024,24 @@ 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; + } + } } index = folio->index + folio_nr_pages(folio) - 1; folio_unlock(folio);
