From 0bd0f9fb190a0fc0fb25b764c8b04869711f7657 Mon Sep 17 00:00:00 2001 From: Eric Paris Date: Mon, 21 Nov 2005 21:32:28 -0800 Subject: [PATCH] [PATCH] hugetlb: fix race in set_max_huge_pages for multiple updaters of nr_huge_pages If there are multiple updaters to /proc/sys/vm/nr_hugepages simultaneously it is possible for the nr_huge_pages variable to become incorrect. There is no locking in the set_max_huge_pages function around alloc_fresh_huge_page which is able to update nr_huge_pages. Two callers to alloc_fresh_huge_page could race against each other as could a call to alloc_fresh_huge_page and a call to update_and_free_page. This patch just expands the area covered by the hugetlb_lock to cover the call into alloc_fresh_huge_page. I'm not sure how we could say that a sysctl section is performance critical where more specific locking would be needed. My reproducer was to run a couple copies of the following script simultaneously while [ true ]; do echo 1000 > /proc/sys/vm/nr_hugepages echo 500 > /proc/sys/vm/nr_hugepages echo 750 > /proc/sys/vm/nr_hugepages echo 100 > /proc/sys/vm/nr_hugepages echo 0 > /proc/sys/vm/nr_hugepages done and then watch /proc/meminfo and eventually you will see things like HugePages_Total: 100 HugePages_Free: 109 After applying the patch all seemed well. Signed-off-by: Eric Paris Acked-by: William Irwin Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/hugetlb.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 728e9bda12e..3e52df7c471 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -22,6 +22,10 @@ unsigned long max_huge_pages; static struct list_head hugepage_freelists[MAX_NUMNODES]; static unsigned int nr_huge_pages_node[MAX_NUMNODES]; static unsigned int free_huge_pages_node[MAX_NUMNODES]; + +/* + * Protects updates to hugepage_freelists, nr_huge_pages, and free_huge_pages + */ static DEFINE_SPINLOCK(hugetlb_lock); static void enqueue_huge_page(struct page *page) @@ -61,8 +65,10 @@ static struct page *alloc_fresh_huge_page(void) HUGETLB_PAGE_ORDER); nid = (nid + 1) % num_online_nodes(); if (page) { + spin_lock(&hugetlb_lock); nr_huge_pages++; nr_huge_pages_node[page_to_nid(page)]++; + spin_unlock(&hugetlb_lock); } return page; } -- 2.20.1