On Mon, Sep 20, 2021 at 05:38:59AM -0700, Paul E. McKenney wrote: > > Well, the block code already does a bdi_unregister in del_gendisk. > > So if we end up freeing the whole device bdev with a registered bdi > > something is badly going wrong. Unfortunately the log in this report > > isn't much help on how we got there. IIRC syzbot will eventually spew > > out a reproducer, so it might be worth to wait for that. > > If it does turn out that you need to block in an RCU callback, > queue_rcu_work() can be helpful. This schedules a workqueue from the RCU > callback, allowing the function passed to the preceding INIT_RCU_WORK() > to block. In this case we really should not block here. The problem is that we are hitting the strange bdi auto-unregister misfeature due to a bug elsewhere. Which reminds that I have a patch series to remove this auto unregistration which I need to bring bag once this is fixed. That being said queue_rcu_work would have been really useful in a few places I touched in that past.
