Re: [PATCH bpf-next 0/2] bpf: Track overlapping RCU protection

["Kumar Kartikeya Dwivedi" <memxor@gmail.com>]

On Thu Aug 6, 2026 at 11:13 AM CEST, Kumar Kartikeya Dwivedi wrote:
> On Thu Aug 6, 2026 at 1:39 AM CEST, Ning Ding wrote:
>> Preemption-disabled and IRQ-disabled regions provide RCU protection, but
>> the verifier does not account for them. Current implementation can invalidate
>> a task kptr while another RCU source remains active, or keep it valid
>> after the final source ends.
>>
>> Track these regions and invalidate RCU-protected pointers only after the
>> last protection ends. Add task kptr tests for overlapping protection and
>> final-exit rejection.
>>
>> This follows review of the applied spin-unlock fix series [1].
>>
>> Tested in QEMU/KVM:
>>   ./test_progs -t task_kfunc
>>   ./test_progs -t preempt_lock
>>   ./test_progs -t irq
>>
>
> Overall, looks good. There are various failures in CI, so you might need to
> update or adjust existing selftests.
>
> Make sure to include selftest changes for _existing_ tests within the kernel
> commit making changes, so as to preserve bisection. Your extra tests should
> still go in a separate commit.
>
> Also, do we need that was_in_rcu_cs logic for bpf_spin_lock(). Would it be
> possible to drop it and do it the same way you've done it for other cases?
> If that makes sense, I would fold that cleanup in the first patch as well.
>
> https://patchwork.kernel.org/project/netdevbpf/patch/20260805233940.3966981-2-dingning04@gmail.com
>
> pw-bot: cr
>

I think from cursory look, the reason is that we forced any MEM_RCU pointer to
be invalidated before, even when program wasn't sleepable, which does not happen
now. The failing test used a non-sleepable program. So making it sleepable should
preserve the failure case. In some ways, this is probably an improvement over
current behavior.

>> [1] https://lore.kernel.org/r/20260803112615.3362122-1-dingning04@gmail.com
>>
>> Ning Ding (2):
>>   bpf: Account for preempt and IRQ state in RCU protection
>>   selftests/bpf: Test overlapping RCU protection
>>
>>  kernel/bpf/verifier.c                         |  13 +-
>>  .../selftests/bpf/prog_tests/task_kfunc.c     |   6 +
>>  .../selftests/bpf/progs/task_kfunc_common.h   |   2 +
>>  .../selftests/bpf/progs/task_kfunc_failure.c  |  49 ++++++
>>  .../selftests/bpf/progs/task_kfunc_success.c  | 147 ++++++++++++++++++
>>  5 files changed, 214 insertions(+), 3 deletions(-)
>>
>>
>> base-commit: 11c1e836710dcba03e50454a4eedfdbaf8d3050e