[PATCH 6.6.y] mm: gup: fix infinite loop within __get_longterm_locked

[Wentao Guan <guanwentao@uniontech.com>]

From: Zhaoyang Huang <zhaoyang.huang@unisoc.com>

commit 1aaf8c122918aa8897605a9aa1e8ed6600d6f930 upstream.

We can run into an infinite loop in __get_longterm_locked() when
collect_longterm_unpinnable_folios() finds only folios that are isolated
from the LRU or were never added to the LRU.  This can happen when all
folios to be pinned are never added to the LRU, for example when
vm_ops->fault allocated pages using cma_alloc() and never added them to
the LRU.

Fix it by simply taking a look at the list in the single caller, to see if
anything was added.

[zhaoyang.huang@unisoc.com: move definition of local]
  Link: https://lkml.kernel.org/r/20250122012604.3654667-1-zhaoyang.huang@unisoc.com
Link: https://lkml.kernel.org/r/20250121020159.3636477-1-zhaoyang.huang@unisoc.com
Fixes: 67e139b02d99 ("mm/gup.c: refactor check_and_migrate_movable_pages()")
Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Aijun Sun <aijun.sun@unisoc.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Wentao Guan <guanwentao@uniontech.com>
---
 mm/gup.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index fdd75384160d8..69d259f7bf37e 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1946,14 +1946,14 @@ struct page *get_dump_page(unsigned long addr)
 /*
  * Returns the number of collected pages. Return value is always >= 0.
  */
-static unsigned long collect_longterm_unpinnable_pages(
+static void collect_longterm_unpinnable_pages(
 					struct list_head *movable_page_list,
 					unsigned long nr_pages,
 					struct page **pages)
 {
-	unsigned long i, collected = 0;
 	struct folio *prev_folio = NULL;
 	bool drain_allow = true;
+	unsigned long i;
 
 	for (i = 0; i < nr_pages; i++) {
 		struct folio *folio = page_folio(pages[i]);
@@ -1965,8 +1965,6 @@ static unsigned long collect_longterm_unpinnable_pages(
 		if (folio_is_longterm_pinnable(folio))
 			continue;
 
-		collected++;
-
 		if (folio_is_device_coherent(folio))
 			continue;
 
@@ -1988,8 +1986,6 @@ static unsigned long collect_longterm_unpinnable_pages(
 				    NR_ISOLATED_ANON + folio_is_file_lru(folio),
 				    folio_nr_pages(folio));
 	}
-
-	return collected;
 }
 
 /*
@@ -2082,12 +2078,10 @@ static int migrate_longterm_unpinnable_pages(
 static long check_and_migrate_movable_pages(unsigned long nr_pages,
 					    struct page **pages)
 {
-	unsigned long collected;
 	LIST_HEAD(movable_page_list);
 
-	collected = collect_longterm_unpinnable_pages(&movable_page_list,
-						nr_pages, pages);
-	if (!collected)
+	collect_longterm_unpinnable_pages(&movable_page_list, nr_pages, pages);
+	if (list_empty(&movable_page_list))
 		return 0;
 
 	return migrate_longterm_unpinnable_pages(&movable_page_list, nr_pages,
-- 
2.20.1