linux-kernel - Re: [PATCH v1.1 2/5] IMA: define readcount functions

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Date:	Tue, 02 Nov 2010 08:22:05 -0400
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	Dave Chinner <david@...morbit.com>
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, jmorris@...ei.org,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	eparis@...hat.com, viro@...iv.linux.org.uk,
	Mimi Zohar <zohar@...ibm.com>
Subject: Re: [PATCH v1.1 2/5] IMA: define readcount functions

On Tue, 2010-11-02 at 11:45 +1100, Dave Chinner wrote:
> On Mon, Nov 01, 2010 at 03:45:36PM -0400, Mimi Zohar wrote:
> > Define iget/iput_readcount() functions to be called from the VFS layer.
> 
> Can't say I like the function names. i_readcount_{inc,dec} seem more
> appropriate, especially so they don't get confused with inode
> reference counting...
> 
> Cheers,
> 
> Dave.

Definitely better naming. thanks!

> > +void iput_readcount(struct inode *inode)
> > +{
> > +	spin_lock(&inode->i_lock);
> > +	if (unlikely((atomic_read(&inode->i_readcount) == 0)))
> > +		printk(KERN_INFO "i_readcount: imbalance ino %ld\n",
> > +		       inode->i_ino);
> > +	else
> > +		atomic_dec(&inode->i_readcount);
> > +	spin_unlock(&inode->i_lock);
> > +}
> 
> No need for the lock just to indicate an imbalance. You could just
> use:
> 
> 	if (atomic_dec_return(&inode->i_readcount) < 0) {
> 		.....
> 	}
> 
> Given this is an integrity subsystem, I suspect the correct thing to
> do here is BUG(), not just issue an informational message that
> something is wrong with the integrity tracking....
> 
> Cheers,
> 
> Dave.

Yes, as Eric explained, the testing is a remnant from IMA, when it
wasn't fully integrated in the kernel.

thanks,

Mimi

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