Re: [PATCH net-next] net/sched: unregister lockdep keys in qdisc_create/qdisc_alloc error path

[Ido Schimmel <idosch@idosch.org>]

On Tue, Apr 30, 2024 at 07:11:13PM +0200, Davide Caratti wrote:
> Naresh and Eric report several errors (corrupted elements in the dynamic
> key hash list), when running tdc.py or syzbot. The error path of
> qdisc_alloc() and qdisc_create() frees the qdisc memory, but it forgets
> to unregister the lockdep key, thus causing use-after-free like the
> following one:

[...]

> Fix this ensuring that lockdep_unregister_key() is called before the
> qdisc struct is freed, also in the error path of qdisc_create() and
> qdisc_alloc().
> 
> Fixes: af0cb3fa3f9e ("net/sched: fix false lockdep warning on qdisc root lock")
> Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
> Closes: https://lore.kernel.org/netdev/20240429221706.1492418-1-naresh.kamboju@linaro.org/
> CC: Naresh Kamboju <naresh.kamboju@linaro.org>
> CC: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Davide Caratti <dcaratti@redhat.com>

Reviewed-by: Ido Schimmel <idosch@nvidia.com>

We've also hit the issue on two of our machines running debug kernels. I
started a run with the fix on both and will report tomorrow morning (not
saying you should wait).