From da9b7c651c6517c2de1099136ed87c0c24f864dd Mon Sep 17 00:00:00 2001
From: David Stevens <stevensd@chromium.org>
Date: Tue, 18 Apr 2023 17:40:31 +0900
Subject: [PATCH] mm/shmem: fix race in shmem_undo_range w/THP
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@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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
mm/shmem.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
diff --git a/mm/shmem.c b/mm/shmem.c
index 806741bbe4a68..f7c08e169e423 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1024,7 +1024,24 @@ 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;
+ }
+ }
}
index = folio->index + folio_nr_pages(folio) - 1;
folio_unlock(folio);
--
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