linux-kernel - Re: [PATCH] rculist: list_first_or_null_rcu() should use list_entry

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Message-ID: <20130625185146.GE20051@mtj.dyndns.org>
Date:	Tue, 25 Jun 2013 11:51:46 -0700
From:	Tejun Heo <tj@...nel.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>
Cc:	Fengguang Wu <fengguang.wu@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	Li Zefan <lizefan@...wei.com>,
	Patrick McHardy <kaber@...sh.net>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rculist: list_first_or_null_rcu() should use
 list_entry_rcu()

On Thu, Jun 20, 2013 at 05:32:44PM -0700, Tejun Heo wrote:
> list_first_or_null() should test whether the list is empty and return
> pointer to the first entry if not in a RCU safe manner.  It's broken
> in two ways.
> 
> * It compares __kernel @__ptr with __rcu @__next triggering the
>   following sparse warning.
> 
>   net/core/dev.c:4331:17: error: incompatible types in comparison expression (different address spaces)
> 
> * It doesn't perform rcu_dereference*() and computes the entry address
>   using container_of() directly from the __rcu pointer which is
>   inconsitent with other rculist interface.  As a result, all three
>   in-kernel users - net/core/dev.c, macvlan, cgroup - are buggy.  They
>   dereference the pointer w/o going through read barrier.
> 
> Fix it by making list_first_or_null_rcu() dereference ->next directly
> and then use list_entry_rcu() on it like other rculist accessors.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Fengguang Wu <fengguang.wu@...el.com>
> Cc: Dipankar Sarma <dipankar@...ibm.com>
> Cc: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Li Zefan <lizefan@...wei.com>
> Cc: Patrick McHardy <kaber@...sh.net>
> Cc: stable@...r.kernel.org

Paul, ping.

-- 
tejun
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