linux-kernel - Re: [PATCH] SMACK: Add missing rcu_read_lock/unlock for process capability walk.

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Message-ID: <20110421155832.GU16484@one.firstfloor.org>
Date:	Thu, 21 Apr 2011 17:58:32 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Casey Schaufler <casey@...aufler-ca.com>
Cc:	Andi Kleen <andi@...stfloor.org>, Andi Kleen <ak@...ux.intel.com>,
	jmorris@...ei.org, linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] SMACK: Add missing rcu_read_lock/unlock for process capability walk.

On Wed, Apr 20, 2011 at 05:47:40PM -0700, Casey Schaufler wrote:
> On 4/20/2011 5:08 PM, Andi Kleen wrote:
> >> The global list, yes. The task specific list, no. Modifying the local
> >> list is like any other modification of the cred structure and requires
> >> the cred be copied.
> > But you still need to free it eventually right? And that freeing will
> > need RCU on the reader.
> 
> Entries are never freed from the global list. Someone is working
> on a patch to do that, but is running into - wait for it - locking
> issues.

Then why do you use rcu_read_lock() at all? 

You can drop all the rcu_read_lock()s and probably the other *_rcu 
list accesses then. And my patch is indeed not needed. 

> Entries on the local lists are only freed when the task exits.

You mean the last user of the cred?

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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