On 20.01.25 10:26, zhaoyang.huang wrote:
From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
Infinite loop within __get_longterm_locked detected in an unique usage
of pin_user_pages where the VA's pages are all unpinnable(vm_ops->fault
function allocate pages via cma_alloc for hardware purpose and leave them
out of LRU) Fixing this by have 'collected' reflect the actual number> of pages in movable_folio_list.
Maybe something like:
"
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.
We incorrectly update the "collected" variable even if nothing was
collected. Fix it by incrementing "collected" only when we isolated a
folio and added it to the list of folios to migrate.
"
I assume, long-term these things will not actually be folios, but pages,
and we'll have to skip them in different code -- or assume they can be
longterm pinned even on CMA because they are allocated by the CMA-owning
driver.
Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
---
mm/gup.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/mm/gup.c b/mm/gup.c
index 3b75e631f369..2231ce7221f9 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2341,8 +2341,6 @@ static unsigned long collect_longterm_unpinnable_folios(
if (folio_is_longterm_pinnable(folio))
continue;
- collected++;
-
if (folio_is_device_coherent(folio))
continue;
@@ -2359,6 +2357,8 @@ static unsigned long collect_longterm_unpinnable_folios(
if (!folio_isolate_lru(folio))
continue;
+ collected++;
+
list_add_tail(&folio->lru, movable_folio_list);
node_stat_mod_folio(folio,
NR_ISOLATED_ANON + folio_is_file_lru(folio),
What if folio_isolate_hugetlb() succeeded? The return value can tell us
if it actually succeeded.
--
Cheers,
David / dhildenb
