[RFC PATCH] mm/hugetlb: Avoid soft lockup in set_max_huge_pages()

[Jia He]

In large memory(32TB) powerpc servers, we watched several soft lockup under
stress tests.
The call trace are as follows:
1.
get_page_from_freelist+0x2d8/0xd50  
__alloc_pages_nodemask+0x180/0xc20  
alloc_fresh_huge_page+0xb0/0x190    
set_max_huge_pages+0x164/0x3b0      

2.
prep_new_huge_page+0x5c/0x100             
alloc_fresh_huge_page+0xc8/0x190          
set_max_huge_pages+0x164/0x3b0

This patch is to fix such soft lockup. I thouhgt it is safe to call 
cond_resched() because alloc_fresh_gigantic_page and alloc_fresh_huge_page 
are out of spin_lock/unlock section.

Signed-off-by: Jia He <hejianet@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>

---
 mm/hugetlb.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index addfe4ac..d51759d 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1146,6 +1146,10 @@ static int alloc_fresh_gigantic_page(struct hstate *h,
 
 	for_each_node_mask_to_alloc(h, nr_nodes, node, nodes_allowed) {
 		page = alloc_fresh_gigantic_page_node(h, node);
+
+		/* yield cpu */
+		cond_resched();
+
 		if (page)
 			return 1;
 	}
@@ -1381,6 +1385,10 @@ static int alloc_fresh_huge_page(struct hstate *h, nodemask_t *nodes_allowed)
 
 	for_each_node_mask_to_alloc(h, nr_nodes, node, nodes_allowed) {
 		page = alloc_fresh_huge_page_node(h, node);
+
+		/* yield cpu */
+		cond_resched();
+
 		if (page) {
 			ret = 1;
 			break;
-- 
2.5.0