linux-kernel - Re: DEFINE_IDA causing memory leaks? (was Re: [PATCH 1/2] virtio: fix memory leak of virtio ida cache layers)

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Date:	Thu, 17 Sep 2015 08:51:54 +0200
From:	Hannes Reinecke <hare@...e.de>
To:	"Michael S. Tsirkin" <mst@...hat.com>, Suman Anna <s-anna@...com>
Cc:	linux-scsi@...r.kernel.org, JBottomley@...n.com,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	open-iscsi@...glegroups.com
Subject: Re: DEFINE_IDA causing memory leaks? (was Re: [PATCH 1/2] virtio: fix
 memory leak of virtio ida cache layers)

On 09/17/2015 07:33 AM, Michael S. Tsirkin wrote:
> On Wed, Sep 16, 2015 at 07:29:17PM -0500, Suman Anna wrote:
>> The virtio core uses a static ida named virtio_index_ida for
>> assigning index numbers to virtio devices during registration.
>> The ida core may allocate some internal idr cache layers and
>> an ida bitmap upon any ida allocation, and all these layers are
>> truely freed only upon the ida destruction. The virtio_index_ida
>> is not destroyed at present, leading to a memory leak when using
>> the virtio core as a module and atleast one virtio device is
>> registered and unregistered.
>>
>> Fix this by invoking ida_destroy() in the virtio core module
>> exit.
>>
>> Cc: "Michael S. Tsirkin" <mst@...hat.com>
>> Signed-off-by: Suman Anna <s-anna@...com>
> 
> Interesting.
> Will the same apply to e.g. sd_index_ida in drivers/scsi/sd.c
> or iscsi_sess_ida in drivers/scsi/scsi_transport_iscsi.c?
> 
> If no, why not?
> 
> One doesn't generally expect to have to free global variables.
> Maybe we should forbid DEFINE_IDA in modules?
> 
> James, could you comment on this please?
> 
Well, looking at the code 'ida_destroy' only need to be called
if you want/need to do a general cleanup.
It shouldn't be required if you do correct reference counting
on your objects, and call idr_remove() on each of them.

Unless I'm misreading something.

Seems like a topic for KS; Johannes had a larger patchset recently to
clean up idr, which run into very much the same issues.

Cheers,

Hannes

-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@...e.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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