linux-kernel - [PATCH V2] mm/hugetlb: Avoid soft lockup in set_max_huge

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Date:	Thu, 28 Jul 2016 10:54:02 +0800
From:	Jia He <hejianet@...il.com>
To:	linux-mm@...ck.org
Cc:	linux-kernel@...r.kernel.org, Jia He <hejianet@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Mike Kravetz <mike.kravetz@...cle.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Michal Hocko <mhocko@...e.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: [PATCH V2] mm/hugetlb: Avoid soft lockup in set_max_huge_pages()

In powerpc servers with large memory(32TB), we watched several soft
lockups for hugepage 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 lockups. It is safe to call cond_resched() 
there because it is out of spin_lock/unlock section.

Signed-off-by: Jia He <hejianet@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc: Mike Kravetz <mike.kravetz@...cle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Paul Gortmaker <paul.gortmaker@...driver.com>

---
Changes in V2: move cond_resched to a common calling site in set_max_huge_pages

 mm/hugetlb.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index abc1c5f..9284280 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2216,6 +2216,10 @@ static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count,
 		 * and reducing the surplus.
 		 */
 		spin_unlock(&hugetlb_lock);
+
+		/* yield cpu to avoid soft lockup */
+		cond_resched();
+
 		if (hstate_is_gigantic(h))
 			ret = alloc_fresh_gigantic_page(h, nodes_allowed);
 		else
-- 
2.5.0