(changing subject, add devicetree at vger.kernel.org)

On Tue, Nov 17, 2015 at 11:33:25PM +0100, Julia Lawall wrote:

On Tue, 17 Nov 2015, Brian Norris wrote:

quoted

On Tue, Nov 17, 2015 at 06:48:39PM +0100, Julia Lawall wrote:

quoted

Is this something that should be checked for elsewhere?

I expect the same sort of problem shows up plenty of other places. I
don't think many people use CONFIG_OF_DYNAMIC, so the effects of these
failures probably aren't felt by many.

I tried the following semantic patch:

@@
struct device_node *e;
expression e1;
identifier fld;
@@

 ... when != of_node_get(...)
*(<+...e1->fld...+>) = e
 ... when != of_node_get(...)
 return e1;

basically, this says that a structure field is initilized to a device node 
value, the structure is returned by the containing function, and the 
containing function contains no of_node_get at all.  Certainly this is 
quite constrained, but it does produce a number of examples.

I looked at a few of them:

drivers/clk/ingenic/cgu.c, ingenic_cgu_new
clk/pistachio/clk.c, pistachio_clk_alloc_provider

It looks like the clock core (drivers/clk/clk.c) initially grabs the clk
provider node in of_clk_init(), then drops it after it's initialized,
but most of these providers use of_clk_add_provider(), which seems to
manage the device_node lifetime for the user. So I think these are OK.

drivers/mfd/syscon.c, of_syscon_register

This one looks potentially suspect. Syscon nodes aren't usually directly
managed by a single driver, and the device_node pointer is used for
lookups later...so I think it should keep a kref, and it doesn't.

drivers/of/pdt.c, function of_pdt_create_node

Not real sure about this one.

Any idea whether these need of_node_get?  In all cases the device node 
value comes in as a parameter.

I'm really not an expert on this stuff. I just saw a potential problem
that I happen to be looking at in other subsystems, and I wanted to know
what others thought. I think this discussion should include the DT folks
and the subsystems in question. For one, I'm as interested as anyone in
getting this todo clarified:

Documentation/devicetree/todo.txt
- Document node lifecycle for CONFIG_OF_DYNAMIC

Regards,
Brian