Re: [RFC Patch v2 2/4] mm/mempolicy: unify the preprocessing for mbind and set_mempolicy

[David Rientjes <rientjes@google.com>]

On Thu, 20 May 2021, Feng Tang wrote:

> Currently the kernel_mbind() and kernel_set_mempolicy() do almost
> the same operation for parameter sanity check and preprocessing.
> 
> Add a macro to unify the code to reduce the redundancy, and make
> it easier for changing the pre-processing code in future.
> 
> Signed-off-by: Feng Tang <feng.tang@intel.com>
> ---
>  mm/mempolicy.c | 46 +++++++++++++++++++---------------------------
>  1 file changed, 19 insertions(+), 27 deletions(-)
> 
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 1964cca..0f5bf60 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1460,25 +1460,29 @@ static int copy_nodes_to_user(unsigned long __user *mask, unsigned long maxnode,
>  	return copy_to_user(mask, nodes_addr(*nodes), copy) ? -EFAULT : 0;
>  }
>  
> +#define MPOL_PRE_PROCESS() \

This should be extracted to helper function returning bool, not a macro.

> +	 \
> +	nodemask_t nodes; \
> +	int err; \
> +	unsigned short mode_flags; \
> +	mode_flags = mode & MPOL_MODE_FLAGS; \
> +	mode &= ~MPOL_MODE_FLAGS; \
> +	if (mode >= MPOL_MAX) \
> +		return -EINVAL; \
> +	if ((mode_flags & MPOL_F_STATIC_NODES) && \
> +		(mode_flags & MPOL_F_RELATIVE_NODES)) \
> +		return -EINVAL; \
> +	err = get_nodes(&nodes, nmask, maxnode); \
> +	if (err) \
> +		return err;
> +
>  static long kernel_mbind(unsigned long start, unsigned long len,
>  			 unsigned long mode, const unsigned long __user *nmask,
>  			 unsigned long maxnode, unsigned int flags)
>  {
> -	nodemask_t nodes;
> -	int err;
> -	unsigned short mode_flags;
> +	MPOL_PRE_PROCESS();
>  
>  	start = untagged_addr(start);
> -	mode_flags = mode & MPOL_MODE_FLAGS;
> -	mode &= ~MPOL_MODE_FLAGS;
> -	if (mode >= MPOL_MAX)
> -		return -EINVAL;
> -	if ((mode_flags & MPOL_F_STATIC_NODES) &&
> -	    (mode_flags & MPOL_F_RELATIVE_NODES))
> -		return -EINVAL;
> -	err = get_nodes(&nodes, nmask, maxnode);
> -	if (err)
> -		return err;
>  	return do_mbind(start, len, mode, mode_flags, &nodes, flags);
>  }
>  
> @@ -1493,20 +1497,8 @@ SYSCALL_DEFINE6(mbind, unsigned long, start, unsigned long, len,
>  static long kernel_set_mempolicy(int mode, const unsigned long __user *nmask,
>  				 unsigned long maxnode)
>  {
> -	int err;
> -	nodemask_t nodes;
> -	unsigned short flags;
> -
> -	flags = mode & MPOL_MODE_FLAGS;
> -	mode &= ~MPOL_MODE_FLAGS;
> -	if ((unsigned int)mode >= MPOL_MAX)
> -		return -EINVAL;
> -	if ((flags & MPOL_F_STATIC_NODES) && (flags & MPOL_F_RELATIVE_NODES))
> -		return -EINVAL;
> -	err = get_nodes(&nodes, nmask, maxnode);
> -	if (err)
> -		return err;
> -	return do_set_mempolicy(mode, flags, &nodes);
> +	MPOL_PRE_PROCESS();
> +	return do_set_mempolicy(mode, mode_flags, &nodes);
>  }
>  
>  SYSCALL_DEFINE3(set_mempolicy, int, mode, const unsigned long __user *, nmask,
> -- 
> 2.7.4
> 
>