netdev - Re: [PATCH 3/3] netlink: Lock out table resizes while dumping Netlink sockets

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Message-ID: <20150120153556.GJ20315@casper.infradead.org>
Date:	Tue, 20 Jan 2015 15:35:56 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Patrick McHardy <kaber@...sh.net>
Cc:	davem@...emloft.net, herbert@...dor.apana.org.au,
	paulmck@...ux.vnet.ibm.com, ying.xue@...driver.com,
	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org
Subject: Re: [PATCH 3/3] netlink: Lock out table resizes while dumping
 Netlink sockets

On 01/20/15 at 03:21pm, Patrick McHardy wrote:
> I think its preferrable to make the need to handle NETLINK_F_DUMP_INTR
> as noticable as possible and not hide it. Silent failure is the worst
> kind of failure.

I agree to that. The point here is to avoid unnecessary use of
NETLINK_F_DUMP_INTR if all entries fit into a single message buffer.
 
> Yeah. The point could be made that this is a regression though. We didn't
> require userspace to deal with interruptions before, and the behaviour
> was well defined and acceptable for most cases, its not anymore.
> 
> So I think it should be handled by the kernel, without changes to
> userspace.

nl_table_lock was released between individual messages just like
ht->mutex is released with this change.

What changed is that inserts and removal can now occur *while* the
message is being constructed whereas previously they could only
occur between message construction periods. In either case, the dump
would end up missing entries or showing duplicates.
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