netdev - Re: [PATCH net] net: pktgen: remove rcu locking in pktgen_change

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Message-Id: <20161017.105348.849516001766766698.davem@davemloft.net>
Date:   Mon, 17 Oct 2016 10:53:48 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     eric.dumazet@...il.com
Cc:     netdev@...r.kernel.org, brouer@...hat.com, jsperbeck@...gle.com
Subject: Re: [PATCH net] net: pktgen: remove rcu locking in
 pktgen_change_name()

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Sat, 15 Oct 2016 17:50:49 +0200

> From: Eric Dumazet <edumazet@...gle.com>
> 
> After Jesper commit back in linux-3.18, we trigger a lockdep
> splat in proc_create_data() while allocating memory from
> pktgen_change_name().
> 
> This patch converts t->if_lock to a mutex, since it is now only
> used from control path, and adds proper locking to pktgen_change_name()
> 
> 1) pktgen_thread_lock to protect the outer loop (iterating threads)
> 2) t->if_lock to protect the inner loop (iterating devices)
> 
> Note that before Jesper patch, pktgen_change_name() was lacking proper
> protection, but lockdep was not able to detect the problem.
> 
> Fixes: 8788370a1d4b ("pktgen: RCU-ify "if_list" to remove lock in next_to_run()")
> Reported-by: John Sperbeck <jsperbeck@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied and queued up for -stable, thanks.