On Wed, Mar 04, 2020 at 01:50:56PM -0500, Tejun Heo wrote: > 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. That's horrid, it's not like block devices are on some "fast path" for tear-down, we should do it correctly. > > 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. That's not ok, a "member object" can only be valid if you have a reference to it. If you remove the object, you then drop the reference, shouldn't that be the correct thing to do? thanks, greg k-h
