Re: [PATCH v4 01/18] of: overlay: add tests to validate kfrees from overlay removal

[Rob Herring]

On Mon, Oct 15, 2018 at 07:37:21PM -0700, frowand.list@xxxxxxxxx wrote:
> From: Frank Rowand <frank.rowand@xxxxxxxx>
> 
> Add checks:
>   - attempted kfree due to refcount reaching zero before overlay
>     is removed
>   - properties linked to an overlay node when the node is removed
>   - node refcount > one during node removal in a changeset destroy,
>     if the node was created by the changeset
> 
> After applying this patch, several validation warnings will be
> reported from the devicetree unittest during boot due to
> pre-existing devicetree bugs. The warnings will be similar to:
> 
>   OF: ERROR: of_node_release() overlay node /testcase-data/overlay-node/test-bus/test-unittest11/test-unittest111 contains unexpected properties
>   OF: ERROR: memory leak - destroy cset entry: attach overlay node /testcase-data-2/substation@100/hvac-medium-2 expected refcount 1 instead of 2.  of_node_get() / of_node_put() are unbalanced for this node.

These messages could be formatted more consistently. Put the path either 
at the beginning (after any prefix) or end. Beginning is more like a 
compiler error. End puts what the problem is before it's off the edge of 
the screen. 

> Signed-off-by: Frank Rowand <frank.rowand@xxxxxxxx>
> ---
> Changes since v3:
>   - Add expected value of refcount for destroy cset entry error.  Also
>     explain the cause of the error.
> 
>  drivers/of/dynamic.c | 29 +++++++++++++++++++++++++++++
>  drivers/of/overlay.c |  1 +
>  include/linux/of.h   | 15 ++++++++++-----
>  3 files changed, 40 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
> index f4f8ed9b5454..24c97b7a050f 100644
> --- a/drivers/of/dynamic.c
> +++ b/drivers/of/dynamic.c
> @@ -330,6 +330,25 @@ void of_node_release(struct kobject *kobj)
>  	if (!of_node_check_flag(node, OF_DYNAMIC))
>  		return;
>  
> +	if (of_node_check_flag(node, OF_OVERLAY)) {
> +
> +		if (!of_node_check_flag(node, OF_OVERLAY_FREE_CSET)) {

I worry the flags are getting unwieldy.

> +			/* premature refcount of zero, do not free memory */
> +			pr_err("ERROR: memory leak %s() overlay node %pOF before free overlay changeset\n",
> +			       __func__, node);
> +			return;
> +		}
> +
> +		/*
> +		 * If node->properties non-empty then properties were added
> +		 * to this node either by different overlay that has not
> +		 * yet been removed, or by a non-overlay mechanism.
> +		 */
> +		if (node->properties)
> +			pr_err("ERROR: %s() overlay node %pOF contains unexpected properties\n",
> +			       __func__, node);
> +	}
> +
>  	property_list_free(node->properties);
>  	property_list_free(node->deadprops);
>  
> @@ -434,6 +453,16 @@ struct device_node *__of_node_dup(const struct device_node *np,
>  
>  static void __of_changeset_entry_destroy(struct of_changeset_entry *ce)
>  {
> +	if (ce->action == OF_RECONFIG_ATTACH_NODE &&
> +	    of_node_check_flag(ce->np, OF_OVERLAY)) {
> +		if (kref_read(&ce->np->kobj.kref) > 1) {
> +			pr_err("ERROR: memory leak - destroy cset entry: attach overlay node %pOF expected refcount 1 instead of %d.  of_node_get() / of_node_put() are unbalanced for this node.\n",
> +			       ce->np, kref_read(&ce->np->kobj.kref));
> +		} else {
> +			of_node_set_flag(ce->np, OF_OVERLAY_FREE_CSET);
> +		}
> +	}
> +
>  	of_node_put(ce->np);
>  	list_del(&ce->node);
>  	kfree(ce);
> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> index eda57ef12fd0..1176cb4b6e4e 100644
> --- a/drivers/of/overlay.c
> +++ b/drivers/of/overlay.c
> @@ -373,6 +373,7 @@ static int add_changeset_node(struct overlay_changeset *ovcs,
>  			return -ENOMEM;
>  
>  		tchild->parent = target_node;
> +		of_node_set_flag(tchild, OF_OVERLAY);
>  
>  		ret = of_changeset_attach_node(&ovcs->cset, tchild);
>  		if (ret)
> diff --git a/include/linux/of.h b/include/linux/of.h
> index 4d25e4f952d9..aa1dafaec6ae 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -138,11 +138,16 @@ static inline void of_node_put(struct device_node *node) { }
>  extern struct device_node *of_stdout;
>  extern raw_spinlock_t devtree_lock;
>  
> -/* flag descriptions (need to be visible even when !CONFIG_OF) */
> -#define OF_DYNAMIC	1 /* node and properties were allocated via kmalloc */
> -#define OF_DETACHED	2 /* node has been detached from the device tree */
> -#define OF_POPULATED	3 /* device already created for the node */
> -#define OF_POPULATED_BUS	4 /* of_platform_populate recursed to children of this node */
> +/*
> + * struct device_node flag descriptions
> + * (need to be visible even when !CONFIG_OF)
> + */
> +#define OF_DYNAMIC		1 /* (and properties) allocated via kmalloc */
> +#define OF_DETACHED		2 /* detached from the device tree */
> +#define OF_POPULATED		3 /* device already created */
> +#define OF_POPULATED_BUS	4 /* platform bus created for children */
> +#define OF_OVERLAY		5 /* allocated for an overlay */
> +#define OF_OVERLAY_FREE_CSET	6 /* in overlay cset being freed */
>  
>  #define OF_BAD_ADDR	((u64)-1)
>  
> -- 
> Frank Rowand <frank.rowand@xxxxxxxx>
>