Re: [PATCH net 2/2] ice: Fix call trace with null VSI during VF reset

[Jakub Kicinski <kuba@kernel.org>]

On Wed, 17 Aug 2022 13:31:00 +0000 Sokolowski, Jan wrote:
> I'd like to send this response in Michal Jaron's name, as he currently cannot respond to this email.
> 
> Generally you are right, it is better idea to try to keep the system
> in a consistent state than adding "if NULL return;" but I don't think
> it will work here. This "if NULL return;" is here because of race
> between two resets and I don't think we can guarantee that this race
> will be not present if we flush the service work before reset. The
> problem is that vf reset is called in the same time from vf on vm and
> from pf. When reset from vf is called and reset form pf don't clear
> rings yet we must go into ice_reset_vf and clear those rings without
> triggering second reset. If we don't clear rings there we may trigger
> page_frag_cache_drain crash related to writing data to unmapped
> queues. In such cases if there are no vsis we don't need to do this
> and this WARN_ON is not necessary, but we need to check it anyway.

Hm, I assumed there's some synchronization here which we can use 
to prevent the race. After all _something_ must ensure the pointer
returned from ice_get_vf_vsi() will not go away, for instance.

But I'm obviously speculating and Dave already applied the patches 
so moving on.. :)