Post Syndicated from corbet original https://lwn.net/Articles/939389/

It is well understood that concurrency makes programming problems harder;
the high level of concurrency inherent in kernel development is one of the
reasons why kernel work can be challenging. Things can get even worse,
though, if concurrent access happens in places where the code is not
expecting it. The long story accompanying this
short patch from Christian Brauner is illustrative of the kind of
problem that can arise when assumptions about concurrency prove to be
incorrect.