[PATCH v3 1/2] mm/gup.c: Don't pass gup_flags to check_and_migrate_movable_pages()

From: Alistair Popple
Date: Mon Aug 08 2022 - 20:16:47 EST


gup_flags is passed to check_and_migrate_movable_pages() so that it can
call either put_page() or unpin_user_page() to drop the page reference.
However check_and_migrate_movable_pages() is only called for
FOLL_LONGTERM, which implies FOLL_PIN so there is no need to pass
gup_flags.

Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>

---

Changes for v3:

- Move WARN_ON() out of loop
---
mm/gup.c | 23 ++++++++++-------------
1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index c6d060d..a2baa8b 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1907,8 +1907,7 @@ struct page *get_dump_page(unsigned long addr)
* Return negative error if migration fails.
*/
static long check_and_migrate_movable_pages(unsigned long nr_pages,
- struct page **pages,
- unsigned int gup_flags)
+ struct page **pages)
{
unsigned long isolation_error_count = 0, i;
struct folio *prev_folio = NULL;
@@ -1941,10 +1940,8 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
* Migration will fail if the page is pinned, so convert
* the pin on the source page to a normal reference.
*/
- if (gup_flags & FOLL_PIN) {
- get_page(&folio->page);
- unpin_user_page(&folio->page);
- }
+ get_page(&folio->page);
+ unpin_user_page(&folio->page);

ret = migrate_device_coherent_page(&folio->page);
if (ret)
@@ -1998,10 +1995,7 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
if (!pages[i])
continue;

- if (gup_flags & FOLL_PIN)
- unpin_user_page(pages[i]);
- else
- put_page(pages[i]);
+ unpin_user_page(pages[i]);
}

if (!list_empty(&movable_page_list)) {
@@ -2023,8 +2017,7 @@ static long check_and_migrate_movable_pages(unsigned long nr_pages,
}
#else
static long check_and_migrate_movable_pages(unsigned long nr_pages,
- struct page **pages,
- unsigned int gup_flags)
+ struct page **pages)
{
return nr_pages;
}
@@ -2047,13 +2040,17 @@ static long __gup_longterm_locked(struct mm_struct *mm,
if (!(gup_flags & FOLL_LONGTERM))
return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
NULL, gup_flags);
+ /* check_and_migrate_movable_pages() assumes pages have been pinned. */
+ if (WARN_ON(!(gup_flags & FOLL_PIN)))
+ return -EINVAL;
flags = memalloc_pin_save();
do {
rc = __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
NULL, gup_flags);
if (rc <= 0)
break;
- rc = check_and_migrate_movable_pages(rc, pages, gup_flags);
+
+ rc = check_and_migrate_movable_pages(rc, pages);
} while (!rc);
memalloc_pin_restore(flags);


base-commit: 360614c01f81f48a89d8b13f8fa69c3ae0a1f5c7
--
git-series 0.9.1