afs: Don't use mutex for I/O operation lock

Don't use the standard mutex for the I/O operation lock, but rather
implement our own as the standard mutex must be released in the same thread
as locked it.  This is a problem when it comes to doing async FetchData
where the lock will be dropped from the workqueue that processed the
incoming data and not from the issuing thread.

Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20241216204124.3752367-12-dhowells@redhat.com


cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
Signed-off-by: Christian Brauner <brauner@kernel.org>