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

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Message-ID: <20210401140652.GT2088@kadam>
Date:   Thu, 1 Apr 2021 17:06:52 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Jason Gunthorpe <jgg@...dia.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 08:25:11AM -0300, Jason Gunthorpe wrote:
> 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

This check is actually more simple, and older.  It just looks for

	device_register(dev);
	...
	kfree(dev);

I've written your proposed check of:

	device_register(&foo->dev);
	...
	kfree(foo); // warning missing device_put(&foo->dev);

But I just did that earler today and it will probably take a couple
iterations to work out the kinks.  Plus I'm off for a small vacation so
it will be a week before I have the results from that.

> 
> 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):

Sure, I can send this (tomorrow).

> 
> 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))

Is calling dev_set_name() without doing a device_initialize() a bug?  I
could write a check for that.

regards,
dan carpenter