Commit a87b9ebf authored Apr 22, 2015 by Thomas Graf Committed by David S. Miller Apr 22, 2015

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



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: ccd57b1b ("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>

parent e2307ed6

lib/rhashtable.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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);

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