linux-kernel - Re: [PATCH 09/62] atm/nicstar: convert to idr

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Date:	Mon, 4 Feb 2013 13:06:40 -0500
From:	chas williams - CONTRACTOR <chas@....nrl.navy.mil>
To:	Tejun Heo <tj@...nel.org>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	rusty@...tcorp.com.au, bfields@...ldses.org,
	skinsbursky@...allels.com, ebiederm@...ssion.com,
	jmorris@...ei.org, axboe@...nel.dk, netdev@...r.kernel.org
Subject: Re: [PATCH 09/62] atm/nicstar: convert to idr_alloc()

On Mon, 4 Feb 2013 09:06:24 -0800
Tejun Heo <tj@...nel.org> wrote:

> Hello, Chas.
> 
> On Mon, Feb 04, 2013 at 09:04:10AM -0500, chas williams - CONTRACTOR wrote:
> > I don't quite understand your comment.  idr_pre_get() returns 0 in the
> > case of failure.
> 
> So, if you do the following,
> 
> 	int id1 = 0, id2 = 0;
> 
> 	if (!id1)
> 		err = idr_get_new_above(&card->idr, handle1, 0, &id1);
> 	if (!id2 && err == 0)
> 		err = idr_get_new_above(&card->idr, handle2, 0, &id2);
> 	if (err)
> 		goto out;
> 									    
> You have no way of telling whether id1/2 are allocated or not.  0 is
> the special "not allocated" value but it also is a valid ID.  The
> error path should be freeing id1/2 if either of them has been
> allocated but it doesn't and can't with 0 as the non-allocated value.

yeah, i see now.  it didn't understand what idr_get_new_above() was
doing with the start id.  i assumed that it would return something
greater than the start id.  i guess it never did return the starting id
(atleast after some initial failure).

additionally, yes, cleaning up if the second allocation failed was never
done.
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