This is a note to let you know that I've just added the patch titled
mm/shmem: fix race in shmem_undo_range w/THP
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-shmem-fix-race-in-shmem_undo_range-w-thp.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 55ac8bbe358bdd2f3c044c12f249fd22d48fe015 Mon Sep 17 00:00:00 2001
From: David Stevens <stevensd@xxxxxxxxxxxx>
Date: Tue, 18 Apr 2023 17:40:31 +0900
Subject: mm/shmem: fix race in shmem_undo_range w/THP
From: David Stevens <stevensd@xxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxxxx: tidy up comment layout]
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1098,7 +1098,24 @@ 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);
}
Patches currently in stable-queue which might be from stevensd@xxxxxxxxxxxx are
queue-6.6/mm-shmem-fix-race-in-shmem_undo_range-w-thp.patch
