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From:   Alistair Popple <apopple@nvidia.com>
To:     linux-mm@kvack.org, akpm@linux-foundation.org
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        "Sierra Guiza, Alejandro (Alex)" <alex.sierra@amd.com>,
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        Ralph Campbell <rcampbell@nvidia.com>,
        David Hildenbrand <david@redhat.com>,
        Matthew Wilcox <willy@infradead.org>,
        Alistair Popple <apopple@nvidia.com>
Subject: [PATCH v4 1/2] mm/gup.c: Don't pass gup_flags to check_and_migrate_movable_pages()
Date:   Fri, 12 Aug 2022 12:13:08 +1000
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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@nvidia.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>

---

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