Re: [syzbot] INFO: rcu detected stall in newstat

[Peter Zijlstra]

On Mon, Nov 29, 2021 at 03:15:16PM +0100, Dmitry Vyukov wrote:

> Right, I missed the "preempt leak: 00000100 -> 00000101" warning. And
> before that there is also "WARNING: inconsistent lock state" warning.
> This reminds me of the issues we had with RCU/LOCKDEP before when an
> RCU warning disabled LOCKDEP tracking, as the result LOCKDEP missed
> part of events (e.g. tracked lock, but missed subsequent unlock) and
> due to races/ordering issues it mis-reported them as nonsensical
> reports.

You're talking about how debug_locks_off() is a hot-racy-mess? That only
matters if you're triggering stuff concurrently which *mostly* doesn't
happen.

I'm also not quite sure how to fix that without globally serializing
everything, which would be super unhappy.