Re: [PATCH v2 3/5] mm: Fix failure to unmap pte on highmem systems

[Mike Rapoport <rppt@kernel.org>]

On Thu, May 18, 2023 at 12:07:25PM +0100, Ryan Roberts wrote:
> The loser of a race to service a pte for a device private entry in the
> swap path previously unlocked the ptl, but failed to unmap the pte. This
> only affects highmem systems since unmapping a pte is a noop on
> non-highmem systems.
> 
> Fixes: 16ce101db85d ("mm/memory.c: fix race when faulting a device private page")
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> Reviewed-by: Zi Yan <ziy@nvidia.com>

Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>

> ---
>  mm/memory.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index f69fbc251198..ed429e20a1bb 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3728,10 +3728,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
>  			vmf->page = pfn_swap_entry_to_page(entry);
>  			vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
>  					vmf->address, &vmf->ptl);
> -			if (unlikely(!pte_same(*vmf->pte, vmf->orig_pte))) {
> -				spin_unlock(vmf->ptl);
> -				goto out;
> -			}
> +			if (unlikely(!pte_same(*vmf->pte, vmf->orig_pte)))
> +				goto unlock;
>  
>  			/*
>  			 * Get a page reference while we know the page can't be
> -- 
> 2.25.1
> 
> 

-- 
Sincerely yours,
Mike.