Re: [RFC PATCH 3/6] mm: nommu: fix an issue on map request to /dev/zero

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Aug 13, 2026 at 02:22:03PM +0100, Matthew Wilcox wrote:
> On Thu, Aug 13, 2026 at 09:19:47PM +0900, Greg Kroah-Hartman wrote:
> > On Thu, Aug 13, 2026 at 03:33:58PM +0900, Hajime Tazaki wrote:
> > > Upon a private file mapping request to /dev/zero, it calls
> > > kernel_read() in do_mmap_private(), getting a failure with the message
> > > like: "kernel reads not supported for file /dev/zero", which is because
> > > zero_fops defined in drivers/char/mem.c has both .read and .read_iter
> > > definitions.
> > 
> > Do you actually use a no-mmu system?
> 
> If you look at Hajime's contributions, you'll see they're far from an AI
> slopper.
> 
> https://lore.kernel.org/linux-mm/?q=hajime+tazaki

That's not what I asked at all.

This patch is fixing /dev/zero which was broken in 2020 for these
systems.  I think my question was a legit one, I was not casting
aspersions about any slop here in any way.

> > > @@ -869,7 +886,11 @@ static vm_flags_t determine_vm_flags(struct file *file,
> > >  
> > >  	vm_flags = calc_vm_prot_bits(prot, 0) | calc_vm_flag_bits(file, flags);
> > >  
> > > -	if (!file) {
> > > +	/* private and file mapping will be marked anonymous later (do_mmap_private()).
> > > +	 * and /dev/zero is marked by them at .mmap_prepare,
> > > +	 * which should be _before_ this point.
> > > +	 */
> > 
> > Wrong coding style for the comment, which is very typical of
> > LLM-generated stuff.  Always rewrite the output of these tools to
> > actually be sane.
> 
> A lot of humans write comments like this too.  Indeed, it used to be
> the preferred style for net/

Yes, but it's not for anything outside of net/

thanks,

greg k-h