Re: [PATCH] dm-mpath: do not change SCSI device handler

[Hannes Reinecke <hare@suse.de>]

On 04/03/2013 02:04 AM, Mikulas Patocka wrote:
> Hi
> 
> This fixes BZ 912245 and 902595.
> 
> Mikulas
> 
> ---
> 
> dm-mpath: do not change SCSI device handler
> 
> This patch prevents the multipath target from changing the device handler.
> This fixes a kernel crash that can happen when changing the device
> handler.
> 
> When we reload a multipath device, there are two instances of the
> multipath target - the first instance that is active and the second
> instance that is being constructed with "ctr" method.
> 
> If the multipath constructor finds out that the device is using a
> different device handler, it detaches the existing handler and attaches a
> new handler. However, the first instance of the multipath target still
> exists and processes requests. If the first instance sends some
> path-management request with scsi_dh_activate and the second instance
> detaches the device handler while the path-management request is in
> flight, a crash happens. The reason for the crash is that the endio
> routine for the path-management request is working with structures that
> were freed when the handler was detached.
> 
> There is no practical need to change device handlers on an active device,
> so this patch disables it.
> 
> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> 

NACK.

This kills multipath startup when scsi_dh_* modules are already loaded.
After boot scsi_dh_* modules might already be loaded without
multipath running.
Multipath might have defined other hardware handlers in the
configuration file, and will re-attach them on startup.

With this patch multipath cannot configure the devices properly and
will abort.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
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