Re: [PATCH 01/17] locking/lockdep: Add lock type enum to explicitly specify read or write locks

[Peter Zijlstra]

On Mon, May 13, 2019 at 05:11:47PM +0800, Yuyang Du wrote:
> + * Note that we have an assumption that a lock class cannot ever be both
> + * read and recursive-read.

We have such locks in the kernel... see:

  kernel/qrwlock.c:queued_read_lock_slowpath()

And yes, that is somewhat unfortunate, but hard to get rid of due to
hysterical raisins.