Re: [PATCH 1/3] block: Fix sysfs queue freeze and limits lock order

[Ming Lei <ming.lei@redhat.com>]

On Mon, Jan 06, 2025 at 09:29:02AM +0100, Christoph Hellwig wrote:
> On Mon, Jan 06, 2025 at 11:31:43AM +0800, Ming Lei wrote:
> > As I mentioned in another thread, freezing queue may not be needed in
> > ->store(), so let's discuss and confirm if it is needed here first.
> > 
> > https://lore.kernel.org/linux-block/Z3tHozKiUqWr7gjO@fedora/
> 
> We do need the freezing.  What you're proposing is playing fast and loose
> which is going to get us in trouble.

It is just soft update from sysfs interface, and both the old and new limits
are correct from device viewpoint.

What is the trouble? We have run the .store() code without freezing for
more than 10 years, no one report issue in the area.


> While most (all?) limits are simple
> scalars, you often can't update just one without the others without
> having coherent state.  Having coherent state was the entire point of
> the atomic queue limit updates.

We am talking all the update in block queue sysfs store(), in each
interface just one scalar number is updated in atomic way.

The atomic update API is still applied, I meant queue freeze can be
removed.


Thank,s
Ming