On Fri, Jun 07, 2024 at 10:16:58AM -0600, Logan Gunthorpe wrote: > > > On 2024-06-06 23:03, Christoph Hellwig wrote: > > On Thu, Jun 06, 2024 at 10:54:06PM +0200, Greg Kroah-Hartman wrote: > >> On Wed, Jun 05, 2024 at 01:29:29PM -0600, Martin Oliveira wrote: > >>> The standard kernfs vm_ops installs a page_mkwrite() operator which > >>> modifies the file update time on write. > >>> > >>> This not always required (or makes sense), such as in the P2PDMA, which > >>> uses the sysfs file as an allocator from userspace. > >> > >> That's not a good idea, please don't do that. sysfs binary files are > >> "pass through", why would you want to use this as an allocator? > > > > I think the real question is why sysfs binary files implement > > page_mkwrite by default. page_mkwrite is needed for file systems that > > need to allocate space from a free space pool, which seems odd for > > sysfs. > > The default page_mkwrite in kernfs just calls file_update_time() but, as > I understand it, the fault code should call file_update_time() if > page_mkwrite isn't set. So perhaps the easiest thing is to simply not > add a page_mkwrite unless the vm_ops adds one. > > It's not the easiest thing to trace, but as best as I can tell there are > no kernfs binary attributes that use page_mkwrite. So alternatively, > perhaps we could just disallow page_mkwrite in kernfs entirely? Sure, let's do that.
