netdev - Re: [PATCH net-next 1/5] sctp: add the rhashtable apis for sctp global transport hashtable

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Message-ID: <20151230174103.GC16270@localhost.localdomain>
Date:	Wed, 30 Dec 2015 15:41:03 -0200
From:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	network dev <netdev@...r.kernel.org>, linux-sctp@...r.kernel.org,
	mleitner@...hat.com, vyasevic@...hat.com, daniel@...earbox.net,
	davem@...emloft.net, Herbert Xu <herbert@...dor.apana.org.au>,
	Xin Long <lucien.xin@...il.com>
Subject: Re: [PATCH net-next 1/5] sctp: add the rhashtable apis for sctp
 global transport hashtable

On Wed, Dec 30, 2015 at 11:50:46PM +0800, Xin Long wrote:
...
> +void sctp_hash_transport(struct sctp_transport *t)
> +{
> +	struct sctp_sockaddr_entry *addr;
> +	struct sctp_hash_cmp_arg arg;
> +
> +	addr = list_entry(t->asoc->base.bind_addr.address_list.next,
> +			  struct sctp_sockaddr_entry, list);
> +	arg.laddr = &addr->a;
> +	arg.paddr = &t->ipaddr;
> +	arg.net   = sock_net(t->asoc->base.sk);
> +
> +reinsert:
> +	if (rhashtable_lookup_insert_key(&sctp_transport_hashtable, &arg,
> +					 &t->node, sctp_hash_params) == -EBUSY)
> +		goto reinsert;
> +}

This is the nasty situation I mentioned in previous email. It seems that
a stress test can trigger a double rehash and cause an entry to not be
added.

This is in fact very near some bugs you caught on rhashtable in the past
few days/couple of weeks tops.

I'm actually against this loop as is. I may have not been clear with Xin
about not adding my signature to the patchset due to this.

Please take a look at Xin's emails on thread 'rhashtable: Prevent
spurious EBUSY errors on insertion' about this particular situation.
Cc'ing Herbert as he wanted to see the patches for that issue.

  Marcelo

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