[PATCH] netfs: Fix netfs_page_mkwrite() to check folio->mapping is valid

[David Howells]

Matthew Wilcox <willy at infradead.org> wrote:

> >  	if (folio_lock_killable(folio) < 0)
> >  		goto out;
> > +	if (folio->mapping != mapping) {
> > +		ret = VM_FAULT_NOPAGE | VM_FAULT_LOCKED;
> > +		goto out;
> > +	}
> 
> Have you tested this?

I've tried to.  generic/247 can trigger it, but the race happens rarely.

> I'd expect it to throw some VM assertions.

I didn't see any.

I guess VM_FAULT_LOCKED is not universally handled by the caller and that I
should unlock the folio myself instead.

David