2018-09-26 11:59:08

by zhong jiang

Subject: [PATCH] powerpc: Move a dereference below a NULL test

It is safe to move dereference below a NULL test.

Signed-off-by: zhong jiang <[email protected]>
---
arch/powerpc/kernel/cacheinfo.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/cacheinfo.c b/arch/powerpc/kernel/cacheinfo.c
index a8f20e5..7f19714 100644
--- a/arch/powerpc/kernel/cacheinfo.c
+++ b/arch/powerpc/kernel/cacheinfo.c
@@ -401,14 +401,13 @@ static struct cache *cache_lookup_or_instantiate(struct device_node *node,
struct cache *cache;

cache = cache_lookup_by_node(node);
+ if (!cache)
+ cache = cache_do_one_devnode(node, level);

WARN_ONCE(cache && cache->level != level,
"cache level mismatch on lookup (got %d, expected %d)\n",
cache->level, level);

- if (!cache)
- cache = cache_do_one_devnode(node, level);
-
return cache;
}

--
1.7.12.4

2018-09-26 14:00:11

by Christophe Leroy

Subject: Re: [PATCH] powerpc: Move a dereference below a NULL test

Le 26/09/2018 à 13:46, zhong jiang a écrit :
> It is safe to move dereference below a NULL test.
>
> Signed-off-by: zhong jiang <[email protected]>
> ---
> arch/powerpc/kernel/cacheinfo.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/kernel/cacheinfo.c b/arch/powerpc/kernel/cacheinfo.c
> index a8f20e5..7f19714 100644
> --- a/arch/powerpc/kernel/cacheinfo.c
> +++ b/arch/powerpc/kernel/cacheinfo.c
> @@ -401,14 +401,13 @@ static struct cache *cache_lookup_or_instantiate(struct device_node *node,
> struct cache *cache;
>
> cache = cache_lookup_by_node(node);
> + if (!cache)
> + cache = cache_do_one_devnode(node, level);

But by doing this, you change the meaning of the following warning. Is
that what you want ? In that case the text of the WARN_ONCE() should be
changed, because the mismatch is not only on lookup now.

Christophe

>
> WARN_ONCE(cache && cache->level != level,
> "cache level mismatch on lookup (got %d, expected %d)\n",
> cache->level, level);
>
> - if (!cache)
> - cache = cache_do_one_devnode(node, level);
> -
> return cache;
> }
>
>

2018-09-26 14:06:57

by zhong jiang

Subject: Re: [PATCH] powerpc: Move a dereference below a NULL test

On 2018/9/26 21:58, Christophe LEROY wrote:
>
>
> Le 26/09/2018 à 13:46, zhong jiang a écrit :
>> It is safe to move dereference below a NULL test.
>>
>> Signed-off-by: zhong jiang <[email protected]>
>> ---
>> arch/powerpc/kernel/cacheinfo.c | 5 ++---
>> 1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/cacheinfo.c b/arch/powerpc/kernel/cacheinfo.c
>> index a8f20e5..7f19714 100644
>> --- a/arch/powerpc/kernel/cacheinfo.c
>> +++ b/arch/powerpc/kernel/cacheinfo.c
>> @@ -401,14 +401,13 @@ static struct cache *cache_lookup_or_instantiate(struct device_node *node,
>> struct cache *cache;
>> cache = cache_lookup_by_node(node);
>> + if (!cache)
>> + cache = cache_do_one_devnode(node, level);
>
> But by doing this, you change the meaning of the following warning. Is that what you want ? In that case the text of the WARN_ONCE() should be changed, because the mismatch is not only on lookup now.
>
Yep, I forget the WARN_ONCE. I think we should just remove it. Thought?

Thanks,
zhong jiang
> Christophe
>
>> WARN_ONCE(cache && cache->level != level,
>> "cache level mismatch on lookup (got %d, expected %d)\n",
>> cache->level, level);
>> - if (!cache)
>> - cache = cache_do_one_devnode(node, level);
>> -
>> return cache;
>> }
>>
>
> .
>

2018-09-26 14:23:44

by Michal Suchánek

Subject: Re: [PATCH] powerpc: Move a dereference below a NULL test

On Wed, 26 Sep 2018 19:46:08 +0800
zhong jiang <[email protected]> wrote:

> It is safe to move dereference below a NULL test.
>
> Signed-off-by: zhong jiang <[email protected]>
> ---
> arch/powerpc/kernel/cacheinfo.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/arch/powerpc/kernel/cacheinfo.c
> b/arch/powerpc/kernel/cacheinfo.c index a8f20e5..7f19714 100644
> --- a/arch/powerpc/kernel/cacheinfo.c
> +++ b/arch/powerpc/kernel/cacheinfo.c
> @@ -401,14 +401,13 @@ static struct cache
> *cache_lookup_or_instantiate(struct device_node *node, struct cache
> *cache;
> cache = cache_lookup_by_node(node);
> + if (!cache)
> + cache = cache_do_one_devnode(node, level);
>
> WARN_ONCE(cache && cache->level != level,

This has also null test so cache should be dereferenced only when
non-null here.

Thanks

Michal

2018-09-26 14:45:00

by zhong jiang

Subject: Re: [PATCH] powerpc: Move a dereference below a NULL test

On 2018/9/26 22:22, Michal Such?nek wrote:
> On Wed, 26 Sep 2018 19:46:08 +0800
> zhong jiang <[email protected]> wrote:
>
>> It is safe to move dereference below a NULL test.
>>
>> Signed-off-by: zhong jiang <[email protected]>
>> ---
>> arch/powerpc/kernel/cacheinfo.c | 5 ++---
>> 1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/cacheinfo.c
>> b/arch/powerpc/kernel/cacheinfo.c index a8f20e5..7f19714 100644
>> --- a/arch/powerpc/kernel/cacheinfo.c
>> +++ b/arch/powerpc/kernel/cacheinfo.c
>> @@ -401,14 +401,13 @@ static struct cache
>> *cache_lookup_or_instantiate(struct device_node *node, struct cache
>> *cache;
>> cache = cache_lookup_by_node(node);
>> + if (!cache)
>> + cache = cache_do_one_devnode(node, level);
>>
>> WARN_ONCE(cache && cache->level != level,
> This has also null test so cache should be dereferenced only when
> non-null here.
:-[ , you're right. I forget WARN_ONCE. please ignore the patch.

Sincerely,
zhong jiang
> Thanks
>
> Michal
>
> .
>