Re: [dm-devel] [PATCH 2/6] scsi_dh : increment the refcounts while calling activate

["Moger, Babu" <Babu Moger lsi com>]

> -----Original Message-----
> From: James Bottomley [mailto:James Bottomley suse de]
> Sent: Thursday, July 29, 2010 7:09 PM
> To: Moger, Babu
> Cc: device-mapper development; linux-scsi vger kernel org; Qi, Yanling;
> Chauhan, Vijay; Stankey, Robert; Dachepalli, Sudhir
> Subject: Re: [PATCH 2/6] scsi_dh : increment the refcounts while
> calling activate
> 
> On Wed, 2010-07-28 at 16:59 -0600, Moger, Babu wrote:
> > Hold the refcounts for device and scsi_dh_data while calling
> handler's
> > activate. This will make sure that devices and scsi_dh_data are not
> > removed while activate is still in progress. Make sure to call
> > put_device and kref_put in the handler after activate is complete.
> 
> This is a complete no-no.  You can't take unreleased references in a
> single patch.  I know the releases come in subsequent patches, but
> that's not the way to do it.  You have to have an atomic change (as in
> all refcounts must balance on either side of the patch).  If someone
> bisected into this, it would likely never release stuff ... which could
> lead to some unnecessary debugging.

  Yes.. Understood. Still investigating to see if I could avoid this..
 
> James
>