netdev - Re: suspicious RCU usage in net/ipv4/ip

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Message-ID: <1389919784.31367.442.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 16 Jan 2014 16:49:44 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Cong Wang <cwang@...pensource.com>
Cc:	paulmck@...ux.vnet.ibm.com, Tom Herbert <therbert@...gle.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: suspicious RCU usage in net/ipv4/ip_tunnel.c:80

On Thu, 2014-01-16 at 16:26 -0800, Cong Wang wrote:
> On Mon, Jan 13, 2014 at 8:53 PM, Paul E. McKenney
> <paulmck@...ux.vnet.ibm.com> wrote:
> > OK, I'll bite...  This code invokes dst_release() which looks to me
> > like it dereferences this pointer:
> >
> 
> Yeah, sure, my point is it doesn't dereference the pointer when it holds
> the spin_lock. I read rcu_dereference_protected() as "deference the rcu
> pointer when we protected by ...", but we dereference it after the lock is
> released. :)

See rcu_dereference_protected() as rcu_fetch_protected()

We read/fetch the pointer, but wont dereference the memory pointer by
this pointer later.

> 
> 
> @Eric, will you submit your patch as a formal one? I already tested it.

I actually sent another patch : 

http://patchwork.ozlabs.org/patch/311902/

Thanks !


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