Another thing that should be considered in the future is performing similar
checks as we perform in free_tail_page_prepare() -- checking pincount etc.
-- when freeing a large fsdax folio.
Fixes: 4996fc547f5b ("mm: let _folio_nr_pages overlay memcg_data in first tail page")
Fixes: 38607c62b34b ("fs/dax: properly refcount fs dax pages")
Reported-by: Alison Schofield <alison.schofield@xxxxxxxxx>
Closes: https://lkml.kernel.org/r/Z_W9Oeg-D9FhImf3@xxxxxxxxxxxxxxxxxx
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
fs/dax.c | 1 +
include/linux/mm.h | 17 +++++++++++++++++
2 files changed, 18 insertions(+)
diff --git a/fs/dax.c b/fs/dax.c
index af5045b0f476e..676303419e9e8 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -396,6 +396,7 @@ static inline unsigned long dax_folio_put(struct folio *folio)
order = folio_order(folio);
if (!order)
return 0;
+ folio_reset_order(folio);
for (i = 0; i < (1UL << order); i++) {
struct dev_pagemap *pgmap = page_pgmap(&folio->page);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index b7f13f087954b..bf55206935c46 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1218,6 +1218,23 @@ static inline unsigned int folio_order(const struct folio *folio)
return folio_large_order(folio);
}
+/**
+ * folio_reset_order - Reset the folio order and derived _nr_pages
+ * @folio: The folio.
+ *
+ * Reset the order and derived _nr_pages to 0. Must only be used in the
+ * process of splitting large folios.
+ */
+static inline void folio_reset_order(struct folio *folio)
+{
+ if (WARN_ON_ONCE(!folio_test_large(folio)))
+ return;
+ folio->_flags_1 &= ~0xffUL;
+#ifdef NR_PAGES_IN_LARGE_FOLIO
+ folio->_nr_pages = 0;
+#endif
+}
+
#include <linux/huge_mm.h>
/*
--
2.48.1
