netdev - Re: [PATCH net-next-2.6] net: make sure rtnl is held in rtnl_fill

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Message-ID: <1305734559.2991.50.camel@edumazet-laptop>
Date:	Wed, 18 May 2011 18:02:39 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next-2.6] net: make sure rtnl is held in
 rtnl_fill_ifinfo()

Le mercredi 18 mai 2011 à 11:35 +0200, Eric Dumazet a écrit :
> Commit e67f88dd12f610 (net: dont hold rtnl mutex during netlink dump
> callbacks) added a problem in rtnl_fill_ifinfo() not being always called
> with RTNL held, which is racy.
> 
> 1) This patch extends rtnl_mutex helper functions so that :
> 
> rtnl_lock() is able to BUG_ON() if recursively called.
> [This was only provided if LOCKDEP was on]
> 
> rtnl_is_locked() is able to check if current thread owns rtnl_mutex
> [ASSERT_RTNL() gets this added feature too]
> 
> 2) Add one ASSERT_RTNL() in rtnl_fill_ifinfo()
> 
> 3) Make sure rtnl is held in rtnl_dump_ifinfo()
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
> --

Hmm, please disregard, there is a lock depency problem here

netlink_dump() does a mutex_lock(nlk->cb_mutex)
So if we try to lock rtnl_mutex later in rtnl_dump_ifinfo(), we can
deadlock with another task doing the reverse.

(first lock rtnl_mutex, then nlk->cb_mutex)




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