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From:   Alan Tull <atull@kernel.org>
Date:   Wed, 17 Oct 2018 16:30:13 -0500
Message-ID: <CANk1AXS-DMhA3=8v9N28K_V6K18HcgN_Esuo=-ddmeBLO46-Rw@mail.gmail.com>
Subject: Re: [PATCH v4 01/18] of: overlay: add tests to validate kfrees from
 overlay removal
To:     Frank Rowand <frowand.list@gmail.com>
Cc:     Rob Herring <robh+dt@kernel.org>,
        Pantelis Antoniou <pantelis.antoniou@konsulko.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Moritz Fischer <mdf@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@vger.kernel.org>, linux-fpga@vger.kernel.org
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On Mon, Oct 15, 2018 at 9:39 PM <frowand.list@gmail.com> wrote:

Hi Frank,

>
> From: Frank Rowand <frank.rowand@sony.com>
>
> 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.
>
> Signed-off-by: Frank Rowand <frank.rowand@sony.com>
> ---
> 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)) {
> +                       /* 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));

Still testing as much as I have time to do.

I'm hitting this error message once when removing an overlay that adds
several child nodes.  The only node I get the message for was a node
that added a fixed-clock (the other nodes didn't trigger the error).
Then even if I edited all the rest of the overlay DTS and removed all
other child nodes and all references to the clock from other nodes, I
still got the error.

Removing dtbo: 1-socfpga_arria10_socdk_sdmmc_ghrd_ovl_ext_cfg.dtb
[   72.032270] OF: ERROR: memory leak - destroy cset entry: attach
overlay node /soc/base_fpga_region/clk_0 expected refcount 1 instead
of 2.  of_node_get() / of_node_put() are unbalanced for this node.

Here's the very stripped down overlay:

/dts-v1/;
/plugin/;
/ {
        fragment@0 {
                target-path = "/soc/base_fpga_region";
                #address-cells = <1>;
                #size-cells = <1>;

                __overlay__ {
                        external-fpga-config;

                        #address-cells = <1>;
                        #size-cells = <1>;

                        clk_0: clk_0 {
                                compatible = "fixed-clock";
                                #clock-cells = <0>;
                                clock-frequency = <100000000>;  /* 100.00 MHz */
                                clock-output-names = "clk_0-clk";
                        };
                };
        };
};

I'll look at it some more tomorrow and try to figure out what's
special about this node.

Alan

> +               } 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@sony.com>
>