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rhashtable: Fix reader/rehash race

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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 <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Herbert Xu 2015-03-12 22:07:49 +11:00 • committed by David S. Miller
commit 9497df88ab
1 changed files with 6 additions and 0 deletions
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6
lib/rhashtable.c
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@ -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))