netdev - Re: RCU lock bug in 3.0.21 (bisected to: 682cb56a, fix NULL dereferences in check_peer

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Message-ID: <20120327051120.GM2450@linux.vnet.ibm.com>
Date:	Mon, 26 Mar 2012 22:11:20 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Ben Greear <greearb@...delatech.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	gregkh@...uxfoundation.org
Subject: Re: RCU lock bug in 3.0.21 (bisected to: 682cb56a, fix NULL
 dereferences in check_peer_redir)

On Tue, Mar 27, 2012 at 02:07:14AM +0200, Eric Dumazet wrote:
> On Mon, 2012-03-26 at 16:46 -0700, Ben Greear wrote:
> 
> > The 3.0.21 kernel doesn't appear to have a rcu_read_lock_return(),
> > so I can't use your patch below.
> 
> This patch was only to show the point (I also CCed Paul, he might have
> some time to think about it, after he clears the inline stuff with
> Linus)

There is an rcu_preempt_depth() that returns rcu_read_lock() nesting
level for CONFIG_PREEMPT_RCU=y on the one hand and returns zero
for CONFIG_PREEMPT_RCU=n on the other.  So if you can reproduce
with CONFIG_PREEMPT_RCU=y, you can substitute rcu_preempt_depth()
rcu_read_lock_return() in Eric's earlier patch.

							Thanx, Paul

> As I said, I was referreing to you adding stuff in rcu. ;)
> 
> Unfortunately I wont have time in the near future to do so myself.
> 
> 
> 

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