netdev - RE: [PATCH 1/2] rhashtable: Introduce rhashtable_walk

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Date:	Mon, 26 Jan 2015 10:09:24 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Herbert Xu' <herbert@...dor.apana.org.au>,
	Thomas Graf <tgraf@...g.ch>, Ying Xue <ying.xue@...driver.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"kaber@...sh.net" <kaber@...sh.net>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"netfilter-devel@...r.kernel.org" <netfilter-devel@...r.kernel.org>
Subject: RE: [PATCH 1/2] rhashtable: Introduce rhashtable_walk_*

From: Herbert Xu
> Some existing rhashtable users get too intimate with it by walking
> the buckets directly.  This prevents us from easily changing the
> internals of rhashtable.
> 
> This patch adds the helpers rhashtable_walk_init/next/end which
> will replace these custom walkers.
> 
> They are meant to be usable for both procfs seq_file walks as well
> as walking by a netlink dump.  The iterator structure should fit
> inside a netlink dump cb structure, with at least one element to
> spare.
...
> +/**
> + * rhashtable_walk_start - Start a hash table walk
> + * @iter:	Hash table iterator
> + *
> + * Start a hash table walk.
> + *
> + * Returns zero if successful.  Returns -EINTR if we couldn't
> + * obtain the resize lock.
> + */
> +int rhashtable_walk_start(struct rhashtable_iter *iter)
> +{
> +	struct rhashtable *ht = iter->ht;
> +	int err;
> +
> +	err = mutex_lock_interruptible(&ht->mutex);
> +	rcu_read_lock();
> +
> +	if (!err)
> +		mutex_unlock(&ht->mutex);
> +
> +	return err;
> +}

That doesn't look right to me.
Surely you shouldn't be calling rcu_read_lock() when the mutex
request is interrupted.

So maybe:
	err = mutex_lock_interruptible(&ht->mutex);
	if (err)
		return err;
	rcu_read_lock();
	return 0;
}

	David
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