[dm-devel] [PATCH 36/57] libmultipath: pass in 'cookie' as argument for dm_addmap()

[Hannes Reinecke]

On 05/03/2016 12:23 AM, Benjamin Marzinski wrote:
> On Wed, Apr 27, 2016 at 01:10:37PM +0200, Hannes Reinecke wrote:
>> Instead of generating the cookie internally we should be
>> passing in the cookie to dm_addmap().
> 
> These look like they could actually cause problems. With
> dm_addmap_create and dm_addmap_reload, you could be in a situation where
> you get a cookie back on your first call to dm_task_set_cookie, wait on
> it, so that cookie is no longer in use, and then use that same cookie
> id again. It's possible that after you first waited on the cookie,
> someone else could have been given that cookie id (without looking into
> the dm cookie code more, I'm not sure how likely this is). If that is
> so, the second call to dm_addmap would be adding its command to the list
> of other commands for that cookie (since you are allowed to use a cookie
> for multiple dm commands). Calling dm_udev_wait would make it wait of
> all the commands.
> 
> We can use a cookie multiple times and then wait on it once. But we
> can't keep reusing the cookie after we've waited on it, because someone
> else could be using the same cookie.
> 
Ah. Thanks for the clarification. I'll be looking into it.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
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