Hello, On Wed, Mar 04, 2020 at 06:22:21PM +0100, Greg Kroah-Hartman wrote: > Ugh, I was dreading the fact that this day might sometime come... > > In theory, the reference counting for struct device shouldn't need to > use rcu at all, right? what is driving the need to use rcu for Lifetime rules in block layer are kinda nebulous. Some of it comes from the fact that some objects are reused. Instead of the usual, create-use-release, they get repurposed to be associated with something else. When looking at such an object from some paths, we don't necessarily have ownership of all of the members. > backing_device_info? Are these being destroyed/used so often that rcu > really is the best solution and the existing reference counting doesn't > work properly? It's more that there are entry points which can only ensure that just the top level object is valid and the member objects might be going or coming as we're looking at it. Thanks. -- tejun
