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Commit 9497df88 authored by Herbert Xu's avatar Herbert Xu Committed by David S. Miller
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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: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 5ff0d16a

lib/rhashtable.c

+6 −0
Original line number Diff line number Diff line
@@ -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 @@ void *rhashtable_lookup_compare(struct rhashtable *ht, const void *key, 
		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))