Re: [BUG] bpf: Soft lockup / panic triggered by bpf_task_release_dtor from NMI on rcu_nocbs CPU

[Justin Suess <utilityemal77@gmail.com>]

On Tue, Apr 21, 2026 at 11:44:42PM +0200, Kumar Kartikeya Dwivedi wrote:
> > [...]
> 
> We can add it but return false when expected_attach_type ==
> BPF_TRACE_ITER. For all other cases, allowing it doesn't make sense
> because these might potentially run in NMI context.
> 
> Please let me know if you'd like to send a fix + tests, otherwise I
> can follow up. Feel free to fold in the diff I sent into your fix, no
> attributation needed.
>
I'll send a fix and selftest.

There needs to be some documentation matrix of prog/attach type to
kptr / other features to prevent bugs like this, but this can be a
future patch.

I may make a series improving documentation as there are many other
verifier "quirks" I had to discover by reading the kernel source. :)

Justin
> > I'm honestly still not sure what the difference is, but they are
> > different [1]
> >
> > Would you rather do this or just reject the dtors with a
> > kfunc filter for this program type?
> >
> > Or teach the verifier that the kptr ops need to be offloaded with
> > bpf_task_work_schedule_resume_impl?
> >
> > [1]: https://docs.ebpf.io/linux/program-type/BPF_PROG_TYPE_TRACING/