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authorDavid Stevens <stevensd@chromium.org>2023-04-18 17:40:31 +0900
committerAndrew Morton <akpm@linux-foundation.org>2023-12-12 17:20:19 -0800
commit55ac8bbe358bdd2f3c044c12f249fd22d48fe015 (patch)
tree9ce5d9290c1f8159bcf17a608afcc7a392f8082d
parent43e8832fed08438e2a27afed9bac21acd0ceffe5 (diff)
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. [akpm@linux-foundation.org: tidy up comment layout] 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 <stevensd@chromium.org> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Suleiman Souhlal <suleiman@google.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
-rw-r--r--mm/shmem.c19
1 files changed, 18 insertions, 1 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index 91e2620148b2..0d1ce70bce38 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1080,7 +1080,24 @@ 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;
+ }
+ }
}
folio_unlock(folio);
}