[PATCH AUTOSEL 4.19 055/101] mm/swap: fix release_pages() when releasing devmap pages

From: Sasha Levin
Date: Fri Jul 19 2019 - 00:24:38 EST

From: Ira Weiny <ira.weiny@xxxxxxxxx>

[ Upstream commit c5d6c45e90c49150670346967971e14576afd7f1 ]

release_pages() is an optimized version of a loop around put_page().
Unfortunately for devmap pages the logic is not entirely correct in
release_pages(). This is because device pages can be more than type
MEMORY_DEVICE_PUBLIC. There are in fact 4 types, private, public, FS DAX,
and PCI P2PDMA. Some of these have specific needs to "put" the page while
others do not.

This logic to handle any special needs is contained in
put_devmap_managed_page(). Therefore all devmap pages should be processed
by this function where we can contain the correct logic for a page put.

Handle all device type pages within release_pages() by calling
put_devmap_managed_page() on all devmap pages. If
put_devmap_managed_page() returns true the page has been put and we
continue with the next page. A false return of put_devmap_managed_page()
means the page did not require special processing and should fall to
"normal" processing.

This was found via code inspection while determining if release_pages()
and the new put_user_pages() could be interchangeable.[1]

[1] https://lkml.kernel.org/r/20190523172852.GA27175@xxxxxxxxxxxxxxxxxxxxxxxxx

Link: https://lkml.kernel.org/r/20190605214922.17684-1-ira.weiny@xxxxxxxxx
Cc: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
mm/swap.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index a3fc028e338e..45fdbfb6b2a6 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -740,15 +740,20 @@ void release_pages(struct page **pages, int nr)
if (is_huge_zero_page(page))

- /* Device public page can not be huge page */
- if (is_device_public_page(page)) {
+ if (is_zone_device_page(page)) {
if (locked_pgdat) {
locked_pgdat = NULL;
- put_devmap_managed_page(page);
- continue;
+ /*
+ * ZONE_DEVICE pages that return 'false' from
+ * put_devmap_managed_page() do not require special
+ * processing, and instead, expect a call to
+ * put_page_testzero().
+ */
+ if (put_devmap_managed_page(page))
+ continue;

page = compound_head(page);