netdev - Re: [PATCH] udp: ipv4: must add synchronization in udp_sk_rx_dst

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Date:	Sun, 15 Dec 2013 10:30:04 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	sbohrer@...advisors.com, netdev@...r.kernel.org
Subject: Re: [PATCH] udp: ipv4: must add synchronization in
 udp_sk_rx_dst_set()

On Wed, 2013-12-11 at 20:22 -0500, David Miller wrote:
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Wed, 11 Dec 2013 14:46:51 -0800
> 
> > From: Eric Dumazet <edumazet@...gle.com>
> > 
> > Unlike TCP, UDP input path does not hold the socket lock.
> > 
> > Before messing with sk->sk_rx_dst, we must use a spinlock, otherwise
> > multiple cpus could leak a refcount.
> > 
> > This patch also takes care of renewing a stale dst entry.
> > (When the sk->sk_rx_dst would not be used by IP early demux)
> > 
> > Fixes: 421b3885bf6d ("udp: ipv4: Add udp early demux")
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> 
> Applied.
> 
> Longterm, perhaps a candidate for using xchg() instead of this
> spinlock?

Indeed... It appears sk_dst_lock should not be used from BH context
anyway...

I am sending a fix, thanks.


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