[PATCH 2/4] mm: hugetlb: skip CMA allocations under PF_MEMALLOC_PIN

[Qi Zheng]

From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>

With gigantic overcommit enabled, a fault during long-term pinning
can allocate a fresh HugeTLB folio from CMA despite PF_MEMALLOC_PIN.

The folio must then be migrated before it can be pinned. However,
fresh gigantic migration targets are not supported, so pinning fails
when the HugeTLB pool has no suitable target, even if the original
fault could have allocated pinnable memory outside CMA.

Honor PF_MEMALLOC_PIN in the HugeTLB CMA allocator so the fault can
try the non-CMA fallback, or fail when allocation is restricted to CMA.

Fixes: eb02f14c4a2b ("mm/hugetlb: allow overcommitting gigantic hugepages")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
---
 mm/hugetlb_cma.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/hugetlb_cma.c b/mm/hugetlb_cma.c
index 95fd2d190f0d2..dde1c866406fb 100644
--- a/mm/hugetlb_cma.c
+++ b/mm/hugetlb_cma.c
@@ -62,6 +62,9 @@ struct folio *hugetlb_cma_alloc_frozen_folio(int order, gfp_t gfp_mask,
 	if (!hugetlb_cma_size)
 		return NULL;
 
+	if (current->flags & PF_MEMALLOC_PIN)
+		return NULL;
+
 retry_cpuset:
 	if (!nodemask) {
 		cpuset_mems_cookie = read_mems_allowed_begin();
-- 
2.54.0