Re: [PATCH v5 5/7] revocable: Add fops replacement

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Oct 17, 2025 at 08:19:06PM +0200, Danilo Krummrich wrote:
> On 10/17/25 6:37 PM, Jason Gunthorpe wrote:
> > On Fri, Oct 17, 2025 at 06:29:10PM +0200, Danilo Krummrich wrote:
> > 
> >> I'm not sure about MISC device though. Unless there's a good reason,
> >> I think MISC device should be "fenced" instead.
> > 
> > misc is a very small wrapper around raw fops, and raw fops are
> > optimized for performance. Adding locking that many important things
> > like normal files don't need to all fops would not be agreed.
> > 
> > The sketch in this series where we have a core helper to provide a
> > shim fops that adds on the lock is smart and I think could be an
> > agreeable way to make a synchronous misc and cdev unregister for
> > everyone to trivially use.
> 
> Sure, for MISC devices without a parent for instance there are no device
> resources to access anyways.

There are many situations with misc that can get people into trouble without
parent:

 misc_deregister(x);
 timer_shutdown_sync(y);
 kfree(z);

For example. It is is buggy if the fops touch y or z.

This is why a _sync version is such a nice clean idea because with 5
letters the above can just be fixed.

Wrapping everything in a revocable would be a huge PITA.

Jason