Re: Hitting BUG_ON in crypto_unregister_alg() on reboot with caamalg_qi2 driver

["Toke Høiland-Jørgensen" <toke@redhat.com>]

Herbert Xu <herbert@gondor.apana.org.au> writes:

> On Thu, Mar 09, 2023 at 03:51:22PM +0100, Toke Høiland-Jørgensen wrote:
>> Hi folks
>> 
>> I'm hitting what appears to be a deliberate BUG_ON() in
>> crypto_unregister_alg() when rebooting my traverse ten64 device on a
>> 6.2.2 kernel (using the Arch linux-aarch64 build, which is basically an
>> upstream kernel).
>> 
>> Any idea what might be causing this? It does not appear on an older
>> (5.17, which is the newest kernel that works reliably, for unrelated
>> reasons).
>
> On the face of it this looks like a generic issue with drivers
> and the Crypto API.  Historically crypto modules weren't meant
> to be removed/unregistered until the last user has freed the tfm.
>
> Obviously with drivers that start unregistering the algorithms when
> the hardware goes away this paradigm breaks.  What should happen is
> that the driver continues to hold onto the crypto algorithm registration
> even when the hardware has gone away.
>
> Some work has to be done in the driver to actually make this safe
> (all the drivers I've looked at are broken in this way).

Hmm, okay; any idea why this started happening with the newer kernel
version? I don't see any changes to the driver that could have caused
this; so is it some core-kernel change that has changed the
order of driver removal on shutdown or something?

Also, absent of a fixed driver (which doesn't sound like it's a trivial
fix?), how do I prevent the system from crashing on shutdown? The
BUG_ON() seems a bit heavy-handed, could it be replaced with a WARN_ON?

-Toke