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    Subjectdevice_node lifetime (was: Re: [PATCH 1/7] phy: brcmstb-sata: add missing of_node_put)
    (changing subject, add devicetree@vger.kernel.org)

    On Tue, Nov 17, 2015 at 11:33:25PM +0100, Julia Lawall wrote:
    > On Tue, 17 Nov 2015, Brian Norris wrote:
    > > On Tue, Nov 17, 2015 at 06:48:39PM +0100, Julia Lawall wrote:
    > > > 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


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