Re: [PATCH 03/20] mm: Use pgoff in struct vm_fault instead of passing it separately

[Jan Kara]

On Fri 14-10-16 12:42:51, Ross Zwisler wrote:
> On Tue, Sep 27, 2016 at 06:08:07PM +0200, Jan Kara wrote:
> > struct vm_fault has already pgoff entry. Use it instead of passing pgoff
> > as a separate argument and then assigning it later.
> > 
> > Signed-off-by: Jan Kara 
> > ---
> >  mm/memory.c | 35 ++-
> >  1 file changed, 18 insertions(+), 17 deletions(-)
> > 
> > diff --git a/mm/memory.c b/mm/memory.c
> > index 447a1ef4a9e3..4c2ec9a9d8af 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -2275,7 +2275,7 @@ static int wp_pfn_shared(struct vm_fault *vmf, pte_t 
> > orig_pte)
> > if (vma->vm_ops && vma->vm_ops->pfn_mkwrite) {
> > struct vm_fault vmf2 = {
> > .page = NULL,
> > -   .pgoff = linear_page_index(vma, vmf->address),
> > +   .pgoff = vmf->pgoff,
> 
> I think there is one path where vmf->pgoff isn't set here.  Here's the path:
> 
> __collapse_huge_page_swapin()
>   do_swap_page()
> do_wp_page()
>   wp_pfn_shared()
> 
> We then use an uninitialized vmf->pgoff to set up vmf2->pgoff, which we pass
> to vm_ops->pfn_mkwrite().
> 
> I think all we need to do to fix this is initialize .pgoff in
> __collapse_huge_page_swapin().  With this one change:
> 
> Reviewed-by: Ross Zwisler 

Thanks for catching this. I don't think that bug had any visible effect
since for anonymous pages (which is what do_swap_page() handles) we won't
enter wp_pfn_shared() but it is definitely good to fix this.

Honza
-- 
Jan Kara 
SUSE Labs, CR
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Re: [PATCH 03/20] mm: Use pgoff in struct vm_fault instead of passing it separately

[Ross Zwisler]

On Tue, Sep 27, 2016 at 06:08:07PM +0200, Jan Kara wrote:
> struct vm_fault has already pgoff entry. Use it instead of passing pgoff
> as a separate argument and then assigning it later.
> 
> Signed-off-by: Jan Kara 
> ---
>  mm/memory.c | 35 ++-
>  1 file changed, 18 insertions(+), 17 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index 447a1ef4a9e3..4c2ec9a9d8af 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -2275,7 +2275,7 @@ static int wp_pfn_shared(struct vm_fault *vmf, pte_t 
> orig_pte)
>   if (vma->vm_ops && vma->vm_ops->pfn_mkwrite) {
>   struct vm_fault vmf2 = {
>   .page = NULL,
> - .pgoff = linear_page_index(vma, vmf->address),
> + .pgoff = vmf->pgoff,

I think there is one path where vmf->pgoff isn't set here.  Here's the path:

__collapse_huge_page_swapin()
  do_swap_page()
do_wp_page()
  wp_pfn_shared()

We then use an uninitialized vmf->pgoff to set up vmf2->pgoff, which we pass
to vm_ops->pfn_mkwrite().

I think all we need to do to fix this is initialize .pgoff in
__collapse_huge_page_swapin().  With this one change:

Reviewed-by: Ross Zwisler 
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