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From: David Howells <dhowells@redhat.com>
In-Reply-To: <20110920143959.GC15859@redhat.com>
References: <20110920143959.GC15859@redhat.com> <20110919214531.GA18085@sergelap> <20110920122202.GA26504@redhat.com> <20110920124419.GA10759@hallyn.com> <20110920134108.GA30749@redhat.com> <20110920143920.GA15859@redhat.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: dhowells@redhat.com, "Serge E. Hallyn" <serge@hallyn.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        "Serge E. Hallyn" <serge.hallyn@canonical.com>,
        lkml <linux-kernel@vger.kernel.org>, richard@nod.at,
        "Eric W. Biederman" <ebiederm@xmission.com>, Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH 2/2] creds: __task_cred(current) doesn't need rcu_read_lock_held()
Date: Tue, 20 Sep 2011 17:19:11 +0100
Message-ID: <5088.1316535551@redhat.com>
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Oleg Nesterov <oleg@redhat.com> wrote:

> Change __task_cred(task) to accept "task == current" without
> rcu_read_lock_held(). This is what current_cred() currently does,
> and with this change __task_cred() becomes more flexible/usable.
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

NAK!

If you compare carefully:

> -	rcu_dereference_protected(current->cred, 1)

and:

> -		rcu_dereference_check(__t->real_cred, 0);		\

you'll notice they aren't quite the same in one very fundamental way.

David