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rhashtable: Do not schedule more than one rehash if we can't grow further

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The current code currently only stops inserting rehashes into the
chain when no resizes are currently scheduled. As long as resizes
are scheduled and while inserting above the utilization watermark,
more and more rehashes will be scheduled.

This lead to a perfect DoS storm with thousands of rehashes
scheduled which lead to thousands of spinlocks to be taken
sequentially.

Instead, only allow either a series of resizes or a single rehash.
Drop any further rehashes and return -EBUSY.

Fixes: ccd57b1bd3 ("rhashtable: Add immediate rehash during insertion")
Signed-off-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:
Thomas Graf 2015-04-22 09:41:46 +02:00 committed by David S. Miller
parent e2307ed6cb
commit a87b9ebf17
1 changed files with 2 additions and 2 deletions
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4
lib/rhashtable.c
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@ -405,8 +405,8 @@ int rhashtable_insert_rehash(struct rhashtable *ht)
if (rht_grow_above_75(ht, tbl))
size *= 2;
/* More than two rehashes (not resizes) detected. */
else if (WARN_ON(old_tbl != tbl && old_tbl->size == size))
/* Do not schedule more than one rehash */
else if (old_tbl != tbl)
return -EBUSY;
new_tbl = bucket_table_alloc(ht, size, GFP_ATOMIC);