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From: David Miller <davem@davemloft.net>
To: fw@strlen.de
Cc: netdev@vger.kernel.org
Subject: Re: [PATCH net-next 0/7] rtnetlink: allow to run selected handlers without rtnl
Date: Wed, 09 Aug 2017 09:41:25 -0700 (PDT)	[thread overview]
Message-ID: <20170809.094125.134674528726147241.davem@davemloft.net> (raw)
In-Reply-To: <20170809081928.GA26899@breakpoint.cc>

From: Florian Westphal <fw@strlen.de>
Date: Wed, 9 Aug 2017 10:19:28 +0200

> David Miller <davem@davemloft.net> wrote:
>> From: Florian Westphal <fw@strlen.de>
>> Date: Tue,  8 Aug 2017 18:02:29 +0200
>> 
>> > Unfortunately RTNL mutex is a performance issue, e.g. a cpu adding
>> > an ip address prevents other cpus from seemingly unrelated tasks
>> > such as dumping tc classifiers.
>> 
>> It is related if somehow the TC entries refer to IP addresses.
>>
>> Someone could create something like that.
> 
> Actually I am not following.  Why would read-only accesses need rtnl
> locking wrt. any other operation (provided of course rtnl lock doesn't
> protect the data structure)?

If the validity of change X depends upon another value Y meeting some
criteria, we test Y and then must be sure that Y doesn't change while
we go about making the change to X.

For example if I need to make sure a path to an IPV4 address exists
configured to an interface when adding a route, I must be sure that
someone can't remove that IPV4 address while I'm adding the route,
after I've checked that it does in fact exist.

This is the kind of stuff that the RTNL mutex ensures.

  reply	other threads:[~2017-08-09 16:41 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-08 16:02 [PATCH net-next 0/7] rtnetlink: allow to run selected handlers without rtnl Florian Westphal
2017-08-08 16:02 ` [PATCH net-next 1/7] rtnetlink: call rtnl_calcit directly Florian Westphal
2017-08-08 16:02 ` [PATCH net-next 2/7] rtnetlink: make rtnl_register accept a flags parameter Florian Westphal
2017-08-08 16:02 ` [PATCH net-next 3/7] rtnetlink: add reference counting to prevent module unload while dump is in progress Florian Westphal
2017-08-08 16:02 ` [PATCH net-next 4/7] rtnetlink: small rtnl lock pushdown Florian Westphal
2017-08-08 16:02 ` [PATCH net-next 5/7] rtnetlink: protect handler table with rcu Florian Westphal
2017-08-08 16:02 ` [PATCH net-next 6/7] rtnetlink: add and use RTNL_FLAG_DOIT_UNLOCKED Florian Westphal
2017-08-08 16:02 ` [PATCH net-next 7/7] net: call newid/getid without rtnl mutex held Florian Westphal
2017-08-09  4:33 ` [PATCH net-next 0/7] rtnetlink: allow to run selected handlers without rtnl David Miller
2017-08-09  8:19   ` Florian Westphal
2017-08-09 16:41     ` David Miller [this message]
2017-08-09 16:42     ` David Miller

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