Remove nid_lock from alloc_fresh_huge_page

The fix to that race in alloc_fresh_huge_page() which could give an illegal
node ID did not need nid_lock at all: the fix was to replace static int nid
by static int prev_nid and do the work on local int nid.  nid_lock did make
sure that racers strictly roundrobin the nodes, but that's not something we
need to enforce strictly.  Kill nid_lock.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 15fc7b000772..2d7611cf276a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -104,15 +104,19 @@ static int alloc_fresh_huge_page(void)
 {
         static int prev_nid;
         struct page *page;
-        static DEFINE_SPINLOCK(nid_lock);
         int nid;
 
-        spin_lock(&nid_lock);
+        /*
+         * Copy static prev_nid to local nid, work on that, then copy it
+         * back to prev_nid afterwards: otherwise there's a window in which
+         * a racer might pass invalid nid MAX_NUMNODES to alloc_pages_node.
+         * But we don't need to use a spin_lock here: it really doesn't
+         * matter if occasionally a racer chooses the same nid as we do.
+         */
         nid = next_node(prev_nid, node_online_map);
         if (nid == MAX_NUMNODES)
                 nid = first_node(node_online_map);
         prev_nid = nid;
-        spin_unlock(&nid_lock);
 
         page = alloc_pages_node(nid, htlb_alloc_mask|__GFP_COMP|__GFP_NOWARN,
                                         HUGETLB_PAGE_ORDER);