netdev - Re: [PATCH] rtnetlink: Fix problem with buffer allocation

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Message-ID: <1329860896.18384.61.camel@edumazet-laptop>
Date:	Tue, 21 Feb 2012 22:48:16 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Greg Rose <gregory.v.rose@...el.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH] rtnetlink: Fix problem with buffer allocation

Le mardi 21 février 2012 à 12:47 -0800, Greg Rose a écrit :

> Modifies the rtnl_calcit function to traverse the list of net
> devices and compute the minimum buffer size that can hold the
> info dumps of all matching devices based upon the filter passed
> in via the new netlink attribute filter mask.  If no filter
> mask is sent then the buffer allocation defaults to NLMSG_GOODSIZE.
> 

...

> +	/*
> +	 * traverse the list of net devices and compute the minimum
> +	 * buffer size based upon the filter mask.
> +	 */
> +	list_for_each_entry_rcu(dev, &net->dev_base_head, dev_list) {
> +		min_ifinfo_dump_size = max_t(u16, min_ifinfo_dump_size,
> +					     if_nlmsg_size(dev,
> +						           ext_filter_mask));
> +	}

Thats going to hurt some setups (thousand of devices on a server).

Also why are you using _rcu() variant here, we hold rtnl I presume ?



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