Re: selftests: tc-testing: tdc.sh: WARNING: at kernel/locking/lockdep.c:1226 lockdep_register_key

[Eric Dumazet]

On Tue, Apr 30, 2024 at 12:17 PM Davide Caratti <dcaratti@xxxxxxxxxx> wrote:
>
> hello,
>
> On Tue, Apr 30, 2024 at 12:17 AM Naresh Kamboju
> <naresh.kamboju@xxxxxxxxxx> wrote:
> >
> > While running selftests: tc-testing: tdc.sh the following kernel warnings,
> > kernel Bug, kernel oops and kernel panic noticed with Linux next-20240429
> > tag kernel as per the available data.
> >
> > This build config is from kselftest merge config[1].
> >
> > Reported-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx>
> >
> > selftests: tc-testing: tdc.sh log and crash log
>
> the problem is created by [1]. I think that at least we need to guard
> against failures to allocate sch->cpu_bstats and sch->cpu_qstats,
> otherwise the dynamic key is registered but never unregistered (though
> the key is freed  in the error path of of qdisc_alloc() ). But there
> might be also something else; however, I can reproduce some similar
> splat, will follow-up on the list.
>
> sorry for the noise,
> --
> davide
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=af0cb3fa3f9ed258d14abab0152e28a0f9593084
>

I just had  5 or 6 syzbot reports about this issue.

I tested the following fix.

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 31dfd6c7405b01e22fe1b8c80944e2bed7d30ddc..d3f6006b563ccd8827b7af362ce9dceaa78f8841
100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -982,6 +982,7 @@ struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,

        return sch;
 errout1:
+       lockdep_unregister_key(&sch->root_lock_key);
        kfree(sch);
 errout:
        return ERR_PTR(err);