From 9497df88ab5567daa001829051c5f87161a81ff0 Mon Sep 17 00:00:00 2001 From: Herbert Xu Date: Thu, 12 Mar 2015 22:07:49 +1100 Subject: [PATCH] rhashtable: Fix reader/rehash race There is a potential race condition between readers and the rehasher. In particular, the rehasher could have started a rehash while the reader finishes a scan of the old table but fails to see the new table pointer. This patch closes this window by adding smp_wmb/smp_rmb. Signed-off-by: Herbert Xu Signed-off-by: David S. Miller --- lib/rhashtable.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/lib/rhashtable.c b/lib/rhashtable.c index 6ffc793145f3..68210cc2bab8 100644 --- a/lib/rhashtable.c +++ b/lib/rhashtable.c @@ -271,6 +271,9 @@ static void rhashtable_rehash(struct rhashtable *ht, */ rcu_assign_pointer(ht->future_tbl, new_tbl); + /* Ensure the new table is visible to readers. */ + smp_wmb(); + for (old_hash = 0; old_hash < old_tbl->size; old_hash++) rhashtable_rehash_chain(ht, old_hash); @@ -618,6 +621,9 @@ restart: return rht_obj(ht, he); } + /* Ensure we see any new tables. */ + smp_rmb(); + old_tbl = tbl; tbl = rht_dereference_rcu(ht->future_tbl, ht); if (unlikely(tbl != old_tbl)) -- 2.20.1