[libvirt] [PATCH 3/3] virNWFilterBindingObjListAddLocked: Produce better error message than 'Duplicate key'

[Cole Robinson]

On 3/19/19 9:49 AM, Michal Privoznik wrote:
> If there are two concurrent threads, one of which is removing an
> nwfilter from the list and the other is trying to add it back they
> may serialize in the following order:
> 
> 1) obj->removing is set and @obj is unlocked.
> 2) The tread that's trying to add the nwfilter onto the list locks
>    the list and tries to find, if the nwfilter already exists.
> 3) Our lookup functions say it doesn't, so the thread proceeds to
>    virHashAddEntry() which fails with 'Duplicate key' error.
> 
> This is obviously not helpful error message at all.
> 
> The problem lies in our lookup function
> (virNWFilterBindingObjListFindByPortDevLocked()) which return
> NULL even if the object is still on the list. They do this so
> that the object is not mistakenly looked up by some API. The fix
> consists of moving 'removing' check one level up and thus
> allowing virNWFilterBindingObjListAddLocked() to produce
> meaningful error message.
> 
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>

Reviewed-by: Cole Robinson <crobinso at redhat.com>

- Cole