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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: b9a8a4195c ("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>
This commit is contained in:
David Stevens 2023-04-18 17:40:31 +09:00 committed by Andrew Morton
parent 43e8832fed
commit 55ac8bbe35
1 changed files with 18 additions and 1 deletions
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19
mm/shmem.c
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@ -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);
}