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lib: fix data race in rhashtable_rehash_one

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rhashtable_rehash_one() uses complex logic to update entry->next field,
after INIT_RHT_NULLS_HEAD and NULLS_MARKER expansion:

entry->next = 1 | ((base + off) << 1)

This can be compiled along the lines of:

entry->next = base + off
entry->next <<= 1
entry->next |= 1

Which will break concurrent readers.

NULLS value recomputation is not needed here, so just remove
the complex logic.

The data race was found with KernelThreadSanitizer (KTSAN).

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Dmitriy Vyukov 2015-09-22 10:51:52 +02:00 committed by David S. Miller
parent 23eedbc243
commit 7def0f952e
1 changed files with 1 additions and 4 deletions
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5
lib/rhashtable.c
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@ -187,10 +187,7 @@ static int rhashtable_rehash_one(struct rhashtable *ht, unsigned int old_hash)
head = rht_dereference_bucket(new_tbl->buckets[new_hash], head = rht_dereference_bucket(new_tbl->buckets[new_hash],
new_tbl, new_hash); new_tbl, new_hash);
if (rht_is_a_nulls(head)) RCU_INIT_POINTER(entry->next, head);
INIT_RHT_NULLS_HEAD(entry->next, ht, new_hash);
else
RCU_INIT_POINTER(entry->next, head);
rcu_assign_pointer(new_tbl->buckets[new_hash], entry); rcu_assign_pointer(new_tbl->buckets[new_hash], entry);
spin_unlock(new_bucket_lock); spin_unlock(new_bucket_lock);