[PATCH] kmemleak: Never return a pointer you didn't 'get'

[PATCH] kmemleak: Never return a pointer you didn't 'get'

[Phil Carmody]

Old - If you don't get the last pointer that you looked at, then it will
still be put, as there's no way of knowing you didn't get it.

New - If you didn't get it, then it refers to something deleted, and
your work is done, so return NULL.

Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com>
---
 mm/kmemleak.c |    8 ++++++--
 1 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 8bf765c..3bf204d 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1350,17 +1350,21 @@ static void *kmemleak_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 	struct kmemleak_object *prev_obj = v;
 	struct kmemleak_object *next_obj = NULL;
 	struct list_head *n = &prev_obj->object_list;
+	int found = 0;
 
 	++(*pos);
 
 	list_for_each_continue_rcu(n, &object_list) {
 		next_obj = list_entry(n, struct kmemleak_object, object_list);
-		if (get_object(next_obj))
+		if (get_object(next_obj)) {
+			found = 1;
 			break;
+		}
 	}
 
 	put_object(prev_obj);
-	return next_obj;
+
+	return found ? next_obj : NULL;
 }
 
 /*
-- 
1.7.2.rc1.37.gf8c40

Re: [PATCH] kmemleak: Never return a pointer you didn't 'get'

[Catalin Marinas]

On Thu, 2011-04-21 at 12:39 +0100, Phil Carmody wrote:
> Old - If you don't get the last pointer that you looked at, then it will
> still be put, as there's no way of knowing you didn't get it.
> 
> New - If you didn't get it, then it refers to something deleted, and
> your work is done, so return NULL.
> 
> Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com>

Good catch. But I think the code may look slightly simpler as below:

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index c1d5867..aacee45 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1414,9 +1414,12 @@ static void *kmemleak_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 	++(*pos);
 
 	list_for_each_continue_rcu(n, &object_list) {
-		next_obj = list_entry(n, struct kmemleak_object, object_list);
-		if (get_object(next_obj))
+		struct kmemleak_object *obj =
+			list_entry(n, struct kmemleak_object, object_list);
+		if (get_object(obj)) {
+			next_obj = obj;
 			break;
+		}
 	}
 
 	put_object(prev_obj);


Thanks.

-- 
Catalin

Re: [PATCH] kmemleak: Never return a pointer you didn't 'get'

[Phil Carmody]

On 27/04/11 10:31 +0100, ext Catalin Marinas wrote:
> On Thu, 2011-04-21 at 12:39 +0100, Phil Carmody wrote:
> > Old - If you don't get the last pointer that you looked at, then it will
> > still be put, as there's no way of knowing you didn't get it.
> > 
> > New - If you didn't get it, then it refers to something deleted, and
> > your work is done, so return NULL.
> > 
> > Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com>
> 
> Good catch. But I think the code may look slightly simpler as below:
> 
> diff --git a/mm/kmemleak.c b/mm/kmemleak.c
> index c1d5867..aacee45 100644
> --- a/mm/kmemleak.c
> +++ b/mm/kmemleak.c
> @@ -1414,9 +1414,12 @@ static void *kmemleak_seq_next(struct seq_file *seq, void *v, loff_t *pos)
>  	++(*pos);
>  
>  	list_for_each_continue_rcu(n, &object_list) {
> -		next_obj = list_entry(n, struct kmemleak_object, object_list);
> -		if (get_object(next_obj))
> +		struct kmemleak_object *obj =
> +			list_entry(n, struct kmemleak_object, object_list);
> +		if (get_object(obj)) {
> +			next_obj = obj;
>  			break;
> +		}
>  	}
>  
>  	put_object(prev_obj);

I did consider that way too, but had no strong preference. I think I now
prefer yours, so please add:

Signed-off-by: Phil Carmody <ext-phil.2.carmody@nokia.com>

Cheers,
Phil