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/mm-shmem-fix-race-in-shmem_undo_range-w-thp.patch
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@xxxxxxxxxxxx>
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@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>
---
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@xxxxxxxxxxxx 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
