2020-08-01 09:09:40

by Wenchao Hao

Subject: [PATCH] mm, mempolicy: Check parameters first in kernel_get_mempolicy

Previous implement called untagged_addr before error check, while
if the error check failed and return EINVAL, the untagged_addr is
just useless work.

Signed-off-by: Wenchao Hao <[email protected]>
---
mm/mempolicy.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 381320671677..dac0cd0df3e1 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1632,11 +1632,11 @@ static int kernel_get_mempolicy(int __user *policy,
int uninitialized_var(pval);
nodemask_t nodes;

- addr = untagged_addr(addr);
-
if (nmask != NULL && maxnode < nr_node_ids)
return -EINVAL;

+ addr = untagged_addr(addr);
+
err = do_get_mempolicy(&pval, &nodes, addr, flags);

if (err)
--
2.25.1

2020-08-04 03:27:39

by Andrew Morton

Subject: Re: [PATCH] mm, mempolicy: Check parameters first in kernel_get_mempolicy

On Sat, 1 Aug 2020 17:08:26 +0800 Wenchao Hao <[email protected]> wrote:

> Previous implement called untagged_addr before error check, while
> if the error check failed and return EINVAL, the untagged_addr is
> just useless work.
>
> ...
>
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1632,11 +1632,11 @@ static int kernel_get_mempolicy(int __user *policy,
> int uninitialized_var(pval);
> nodemask_t nodes;
>
> - addr = untagged_addr(addr);
> -
> if (nmask != NULL && maxnode < nr_node_ids)
> return -EINVAL;
>
> + addr = untagged_addr(addr);
> +
> err = do_get_mempolicy(&pval, &nodes, addr, flags);
>
> if (err)

Well, the compiler will surely avoid that useless work. But the code
is better this way.