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| author | Eric Paris <eparis@redhat.com> | 2005-11-21 21:32:28 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@g5.osdl.org> | 2005-11-22 09:13:43 -0800 |
| commit | 0bd0f9fb190a0fc0fb25b764c8b04869711f7657 (patch) | |
| tree | 0bd7b58c037b5905cf834f27625bd4e0cbb2f3f2 /mm | |
| parent | 5ef897c71a8985b62b7ec320a37376daaad364d0 (diff) | |
| download | lwn-0bd0f9fb190a0fc0fb25b764c8b04869711f7657.tar.gz lwn-0bd0f9fb190a0fc0fb25b764c8b04869711f7657.zip | |
[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 <eparis@redhat.com>
Acked-by: William Irwin <wli@holomorphy.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'mm')
| -rw-r--r-- | mm/hugetlb.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 728e9bda12ea..3e52df7c471b 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; } |