mm/shmem: Fix race in shmem_undo_range w/THP
Subsystems (3)
PATCH v2 1/1 mm/shmem: Fix race in shmem_undo_range w/THP
From: David Stevens <[email protected]>
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")
Signed-off-by David Stevens <[email protected]>
---
v1 -> v2:
- Actually drop pages after splitting a THP
mm/shmem.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-)
mm/shmem.c +16 -1
@@ -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); }
Signature · 1 line
2.40.0.634.g4ca3ef3211-goog