Re: [PATCH v2 1/2] mm/memory: recheck PG_uptodate after ->page_mkwrite()

[Kiryl Shutsemau <kas@kernel.org>]

On Mon, Nov 09, 2026 at 02:11:23PM +0000, Pedro Falcato wrote:
> > diff --git a/mm/memory.c b/mm/memory.c
> > index fe72e66c9c2e..cc1d0b7d15c7 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -5613,6 +5613,18 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
> >  	return VM_FAULT_OOM;
> >  }
> >  
> > +/*
> > + * A page cache folio that is not uptodate holds data that was never read in
> > + * or cleared, and mapping it leaks stale memory to userspace.
> > + */
> > +static bool file_folio_not_uptodate(struct folio *folio)
> > +{
> > +	if (likely(folio_test_uptodate(folio)))
> > +		return false;
> > +	/* Driver pages from ->fault() never get PG_uptodate */
> > +	return !folio_test_anon(folio) && folio->mapping;
> 
> FYI you can wrap this line in an unlikely() and it has the same effect as
> wrapping every call:
> 	return unlikely(!folio_test_anon(folio) && folio->mapping);

I prefer it at the call site. That is where the reader needs to see
that the retry is the rare path.

> > +}
> > +
> >  /*
> >   * Either the VMA lock or the mmap_lock must have been held on entry
> >   * (see FAULT_FLAG_VMA_LOCK) and may have been released depending on
> > @@ -6163,6 +6175,16 @@ static vm_fault_t do_shared_fault(struct vm_fault *vmf)
> >  			folio_put(folio);
> >  			return tmp;
> >  		}
> > +
> > +		/*
> > +		 * The folio was unlocked for ->page_mkwrite(). If it lost
> > +		 * PG_uptodate meanwhile, retry the fault to read it in again.
> > +		 */
> 
> The "read it in again" sounds a bit too prescriptive but, apart from that:

Okay, will drop it if respin needed.

David, could you adjust it on apply otherwise?

> Reviewed-by: Pedro Falcato <pfalcato@suse.de>

Thanks!

-- 
  Kiryl Shutsemau / Kirill A. Shutemov