From 31a459f04109bf0b4d67d9cb2a0e94f0abbead94 Mon Sep 17 00:00:00 2001 From: David Stevens Date: Tue, 18 Apr 2023 17:40:31 +0900 Subject: [PATCH] mm/shmem: fix race in shmem_undo_range w/THP 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 Cc: Matthew Wilcox (Oracle) Cc: Suleiman Souhlal Cc: Signed-off-by: Andrew Morton --- mm/shmem.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/mm/shmem.c b/mm/shmem.c index 91e2620148b2..a77cdebf1206 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -1080,7 +1080,22 @@ 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); } -- 2.50.1