linux-kernel - Re: [PATCH v8 3/3] cgroups: make procs file writable

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Message-ID: <20110322050821.GA11447@ghc17.ghc.andrew.cmu.edu>
Date:	Tue, 22 Mar 2011 01:08:21 -0400
From:	Ben Blum <bblum@...rew.cmu.edu>
To:	Ben Blum <bblum@...rew.cmu.edu>
Cc:	Paul Menage <menage@...gle.com>, linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, akpm@...ux-foundation.org,
	ebiederm@...ssion.com, lizf@...fujitsu.com, matthltc@...ibm.com,
	oleg@...hat.com, David Rientjes <rientjes@...gle.com>,
	Miao Xie <miaox@...fujitsu.com>
Subject: Re: [PATCH v8 3/3] cgroups: make procs file writable

On Thu, Mar 10, 2011 at 01:18:31AM -0500, Ben Blum wrote:
> > > + ? ? ? ? ? ? ? ? ? ? ? /* optimization for the single-task-only case */
> > > + ? ? ? ? ? ? ? ? ? ? ? rcu_read_unlock();
> > > + ? ? ? ? ? ? ? ? ? ? ? cgroup_unlock();
> > > ? ? ? ? ? ? ? ? ? ? ? ?return -ESRCH;
> > > ? ? ? ? ? ? ? ?}
> > >
> > > + ? ? ? ? ? ? ? /*
> > > + ? ? ? ? ? ? ? ?* even if we're attaching all tasks in the thread group, we
> > > + ? ? ? ? ? ? ? ?* only need to check permissions on one of them.
> > > + ? ? ? ? ? ? ? ?*/
> > > ? ? ? ? ? ? ? ?tcred = __task_cred(tsk);
> > > ? ? ? ? ? ? ? ?if (cred->euid &&
> > > ? ? ? ? ? ? ? ? ? ?cred->euid != tcred->uid &&
> > > ? ? ? ? ? ? ? ? ? ?cred->euid != tcred->suid) {
> > > ? ? ? ? ? ? ? ? ? ? ? ?rcu_read_unlock();
> > > + ? ? ? ? ? ? ? ? ? ? ? cgroup_unlock();
> > > ? ? ? ? ? ? ? ? ? ? ? ?return -EACCES;
> > 
> > Maybe turn these returns into "goto out;" statements and put the
> > unlock after the out: label?
> > 
> 
> Maybe; I didn't look too hard at that function. If I revise the patch I
> can do this, though.

Looking back, I think I like it the way it is. Coalescing those unlock
paths would make it less clear... rcu_read is unlocked in the middle of
the function (on the success path), so having a bailout path moves the
failure path far removed from where it's relevant.

-- Ben
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