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    Subject[PATCH v4 02/18] of: overlay: add missing of_node_put() after add new node to changeset
    Date
    From: Frank Rowand <frank.rowand@sony.com>

    The refcount of a newly added overlay node decrements to one
    (instead of zero) when the overlay changeset is destroyed. This
    change will cause the final decrement be to zero.

    After applying this patch, new validation warnings will be
    reported from the devicetree unittest during boot due to
    a pre-existing devicetree bug. The warnings will be similar to:

    OF: ERROR: memory leak of_node_release() overlay node /testcase-data/overlay-node/test-bus/test-unittest4 before free overlay changeset

    This pre-existing devicetree bug will also trigger a WARN_ONCE() from
    refcount_sub_and_test_checked() when an overlay changeset is
    destroyed without having first been applied. This scenario occurs
    when an error in the overlay is detected during the overlay changeset
    creation:

    WARNING: CPU: 0 PID: 1 at lib/refcount.c:187 refcount_sub_and_test_checked+0xa8/0xbc
    refcount_t: underflow; use-after-free.

    (unwind_backtrace) from (show_stack+0x10/0x14)
    (show_stack) from (dump_stack+0x6c/0x8c)
    (dump_stack) from (__warn+0xdc/0x104)
    (__warn) from (warn_slowpath_fmt+0x44/0x6c)
    (warn_slowpath_fmt) from (refcount_sub_and_test_checked+0xa8/0xbc)
    (refcount_sub_and_test_checked) from (kobject_put+0x24/0x208)
    (kobject_put) from (of_changeset_destroy+0x2c/0xb4)
    (of_changeset_destroy) from (free_overlay_changeset+0x1c/0x9c)
    (free_overlay_changeset) from (of_overlay_remove+0x284/0x2cc)
    (of_overlay_remove) from (of_unittest_apply_revert_overlay_check.constprop.4+0xf8/0x1e8)
    (of_unittest_apply_revert_overlay_check.constprop.4) from (of_unittest_overlay+0x960/0xed8)
    (of_unittest_overlay) from (of_unittest+0x1cc4/0x2138)
    (of_unittest) from (do_one_initcall+0x4c/0x28c)
    (do_one_initcall) from (kernel_init_freeable+0x29c/0x378)
    (kernel_init_freeable) from (kernel_init+0x8/0x110)
    (kernel_init) from (ret_from_fork+0x14/0x2c)

    Signed-off-by: Frank Rowand <frank.rowand@sony.com>
    ---
    drivers/of/overlay.c | 4 +++-
    1 file changed, 3 insertions(+), 1 deletion(-)

    diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
    index 1176cb4b6e4e..32cfee68f2e3 100644
    --- a/drivers/of/overlay.c
    +++ b/drivers/of/overlay.c
    @@ -379,7 +379,9 @@ static int add_changeset_node(struct overlay_changeset *ovcs,
    if (ret)
    return ret;

    - return build_changeset_next_level(ovcs, tchild, node);
    + ret = build_changeset_next_level(ovcs, tchild, node);
    + of_node_put(tchild);
    + return ret;
    }

    if (node->phandle && tchild->phandle)
    --
    Frank Rowand <frank.rowand@sony.com>
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