linux-kernel - Re: [bug report] node: Add memory-side caching attributes

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Message-ID: <20210401112511.GV1463678@nvidia.com>
Date:   Thu, 1 Apr 2021 08:25:11 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     kbusch@...nel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [bug report] node: Add memory-side caching attributes

On Thu, Apr 01, 2021 at 12:00:39PM +0300, Dan Carpenter wrote:
> Hi Keith,
> 
> I've been trying to figure out ways Smatch can check for device managed
> resources.  Like adding rules that if we call dev_set_name(&foo->bar)
> then it's device managaged and if there is a kfree(foo) without calling
> device_put(&foo->bar) then that's a resource leak.

It seems to be working from what I can see

Also I wasn't able to convince myself that any locking around
node->cache_attrs exist..

> Of course one of the rules is that if you call device_register(dev) then
> you can't kfree(dev), it has to released with device_put(dev) and that's
> true even if the register fails.  But this code here feels very
> intentional so maybe there is an exception to the rule?

There is no exception. Open coding this:

>    282  free_name:
>    283          kfree_const(dev->kobj.name);

To avoid leaking memory from dev_set_name is a straight up layering
violation, WTF?

node_cacheinfo_release() is just kfree(), so there is no need.
Instead (please feel free to send this Dan):

diff --git a/drivers/base/node.c b/drivers/base/node.c
index f449dbb2c74666..89c28952863977 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -319,25 +319,24 @@ void node_add_cache(unsigned int nid, struct node_cache_attrs *cache_attrs)
 		return;
 
 	dev = &info->dev;
+	device_initialize(dev)
 	dev->parent = node->cache_dev;
 	dev->release = node_cacheinfo_release;
 	dev->groups = cache_groups;
 	if (dev_set_name(dev, "index%d", cache_attrs->level))
-		goto free_cache;
+		goto put_device;
 
 	info->cache_attrs = *cache_attrs;
-	if (device_register(dev)) {
+	if (device_add(dev)) {
 		dev_warn(&node->dev, "failed to add cache level:%d\n",
 			 cache_attrs->level);
-		goto free_name;
+		goto put_device
 	}
 	pm_runtime_no_callbacks(dev);
 	list_add_tail(&info->node, &node->cache_attrs);
 	return;
-free_name:
-	kfree_const(dev->kobj.name);
-free_cache:
-	kfree(info);
+put_device:
+	put_device(dev);
 }
 
 static void node_remove_caches(struct node *node)