6.1-stable review patch. If anyone has any objections, please let me know.
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From: David Hildenbrand david@redhat.com
[ Upstream commit 517f496e1e61bd169d585dab4dd77e7147506322 ]
After commit 1aaf8c122918 ("mm: gup: fix infinite loop within __get_longterm_locked") we are able to longterm pin folios that are not supposed to get longterm pinned, simply because they temporarily have the LRU flag cleared (esp. temporarily isolated).
For example, two __get_longterm_locked() callers can race, or __get_longterm_locked() can race with anything else that temporarily isolates folios.
The introducing commit mentions the use case of a driver that uses vm_ops->fault to insert pages allocated through cma_alloc() into the page tables, assuming they can later get longterm pinned. These pages/ folios would never have the LRU flag set and consequently cannot get isolated. There is no known in-tree user making use of that so far, fortunately.
To handle that in the future -- and avoid retrying forever to isolate/migrate them -- we will need a different mechanism for the CMA area *owner* to indicate that it actually already allocated the page and is fine with longterm pinning it. The LRU flag is not suitable for that.
Probably we can lookup the relevant CMA area and query the bitmap; we only have have to care about some races, probably. If already allocated, we could just allow longterm pinning)
Anyhow, let's fix the "must not be longterm pinned" problem first by reverting the original commit.
Link: https://lkml.kernel.org/r/20250611131314.594529-1-david@redhat.com Fixes: 1aaf8c122918 ("mm: gup: fix infinite loop within __get_longterm_locked") Signed-off-by: David Hildenbrand david@redhat.com Closes: https://lore.kernel.org/all/20250522092755.GA3277597@tiffany/ Reported-by: Hyesoo Yu hyesoo.yu@samsung.com Reviewed-by: John Hubbard jhubbard@nvidia.com Cc: Jason Gunthorpe jgg@ziepe.ca Cc: Peter Xu peterx@redhat.com Cc: Zhaoyang Huang zhaoyang.huang@unisoc.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 [ Revert v6.1.129 commit c986a5fb15ed ] Signed-off-by: Hugh Dickins hughd@google.com Signed-off-by: Sasha Levin sashal@kernel.org --- mm/gup.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c index 37c55e61460e2..599c6b9453166 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -1961,14 +1961,14 @@ struct page *get_dump_page(unsigned long addr) /* * Returns the number of collected pages. Return value is always >= 0. */ -static void collect_longterm_unpinnable_pages( +static unsigned long 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]); @@ -1980,6 +1980,8 @@ static void collect_longterm_unpinnable_pages( if (folio_is_longterm_pinnable(folio)) continue;
+ collected++; + if (folio_is_device_coherent(folio)) continue;
@@ -2001,6 +2003,8 @@ static void collect_longterm_unpinnable_pages( NR_ISOLATED_ANON + folio_is_file_lru(folio), folio_nr_pages(folio)); } + + return collected; }
/* @@ -2093,10 +2097,12 @@ 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);
- collect_longterm_unpinnable_pages(&movable_page_list, nr_pages, pages); - if (list_empty(&movable_page_list)) + collected = collect_longterm_unpinnable_pages(&movable_page_list, + nr_pages, pages); + if (!collected) return 0;
return migrate_longterm_unpinnable_pages(&movable_page_list, nr_pages,