netdev - Re: IPF Montvale machine panic when running a network-relevent testing

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Message-Id: <20080617.203703.254889774.davem@davemloft.net>
Date:	Tue, 17 Jun 2008 20:37:03 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	yanmin_zhang@...ux.intel.com
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-ia64@...r.kernel.org
Subject: Re: IPF Montvale machine panic when running a network-relevent
 testing

From: "Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Date: Wed, 18 Jun 2008 11:27:43 +0800

> This issue is caused by tcp defer accept. Mostly, process context calls lock_sock
> to apply a sleeping lock. BH (SoftIRQ) context calls bh_lock_sock(_nested) to just apply
> for the sk->sk_lock.slock without sleeping, then do appropriate processing based on
> if sk->sk_lock.owned==0. That works well if both process context and BH context operate
> the same sk at the same time. But with tcp defer accept, it doesn't, because
> process context(for example, in inet_csk_accept) locks the listen sk, while BH
> context (in tcp_v4_rcv, for example) locks the child sk and calls
> tcp_defer_accept_check => inet_csk_reqsk_queue_add => reqsk_queue_add, so there is a race
> to access the listen sock.
> 
> Below patch against 2.6.26-rc6 fixes the issue.
> 
> Signed-off-by: Zhang Yanmin <yanmin.zhang@...el.com>

We reverted the guilty defer accept changes, please test Linus's
current tree.