netdev - Re: Warning in net/ipv4/af

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Message-Id: <20100526.005634.48509140.davem@davemloft.net>
Date:	Wed, 26 May 2010 00:56:34 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	anton@...ba.org
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org
Subject: Re: Warning in net/ipv4/af_inet.c:154

From: Anton Blanchard <anton@...ba.org>
Date: Wed, 26 May 2010 13:19:43 +1000

> I notice we update sk_forward_alloc in sk_mem_charge and sk_mem_uncharge.
> Since it isn't an atomic variable I went looking for a lock somewhere in
> the call chain (first thought was the socket lock). I couldn't find
> anything, but I could easily be missing something.

We take the lock properly for all of the skb_queue_rcv_skb() cases
but this rule isn't followed properly for skb_queue_err_skb().

Eric, look at even things like skb_tstamp_tx().  Nothing locks the
socket in those cases, yet we dip down into sock_queue_err_skb() and
thus invoke skb_set_owner_r which goes into sk_mem_charge() and does
the non-atomic update on ->sk_forward_alloc.

I am sure there are other cases with this problem involving
sock_queue_err_skb()...  ip_icmp_error() (via __udp4_lib_err()),
ipv6_icmp_error(), etc.
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