linux-kernel - Re: [PATCH 01/10] Fix idr

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Date:	Mon, 05 May 2008 11:26:49 +0200
From:	Nadia Derbey <Nadia.Derbey@...l.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	manfred@...orfullife.com, paulmck@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org, efault@....de
Subject: Re: [PATCH 01/10] Fix idr_remove()

Andrew Morton wrote:
> On Tue, 29 Apr 2008 16:33:05 +0200
> Nadia.Derbey@...l.net wrote:
> 
> 
>>[PATCH 01/10]
>>
>>This patch fixes idr_remove(): the return inside the loop makes us free only
>>a single layer.
>>
>>Signed-off-by: Nadia Derbey <Nadia.Derbey@...l.net>
>>
>>---
>> lib/idr.c |    2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>>Index: linux-2.6.25-mm1/lib/idr.c
>>===================================================================
>>--- linux-2.6.25-mm1.orig/lib/idr.c	2008-04-25 15:29:00.000000000 +0200
>>+++ linux-2.6.25-mm1/lib/idr.c	2008-04-25 15:48:34.000000000 +0200
>>@@ -385,8 +385,8 @@ void idr_remove(struct idr *idp, int id)
>> 	while (idp->id_free_cnt >= IDR_FREE_MAX) {
>> 		p = alloc_layer(idp);
>> 		kmem_cache_free(idr_layer_cache, p);
>>-		return;
>> 	}
>>+	return;
>> }
>> EXPORT_SYMBOL(idr_remove);
> 
> 
> erk, ancient bug.
> 
> I _think_ the implications of this are that an idr tree will grow fatter
> than it needs to be, but there is no permanent leak: idr_destroy() will
> still free everything, yes?

Yes, exactly. Actually, I've not checked whether all the kernel 
components call idr_destroy() when needed.

> 
> And a consequence of the fix is that idr manipulations will now result in
> more allocs and frees,

Not necessarily more allocs: this loop keeps IDR_FREE_MAX layers in the 
free list. So idr_pre_get() should be a noop.

> but the amount of memory which a tree uses will be
> less?
> 
> 
> 

Regards,
Nadia


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