On Fri, Jan 24, 2020 at 02:42:16PM -0800, Douglas Anderson wrote:
> When I got my clock parenting slightly wrong I ended up with a crash
> that looked like this:
>
> Unable to handle kernel NULL pointer dereference at virtual
> address 0000000000000000
> ...
> pc : clk_hw_get_rate+0x14/0x44
> ...
> Call trace:
> clk_hw_get_rate+0x14/0x44
> _freq_tbl_determine_rate+0x94/0xfc
> clk_rcg2_determine_rate+0x2c/0x38
> clk_core_determine_round_nolock+0x4c/0x88
> clk_core_round_rate_nolock+0x6c/0xa8
> clk_core_round_rate_nolock+0x9c/0xa8
> clk_core_set_rate_nolock+0x70/0x180
> clk_set_rate+0x3c/0x6c
> of_clk_set_defaults+0x254/0x360
> platform_drv_probe+0x28/0xb0
> really_probe+0x120/0x2dc
> driver_probe_device+0x64/0xfc
> device_driver_attach+0x4c/0x6c
> __driver_attach+0xac/0xc0
> bus_for_each_dev+0x84/0xcc
> driver_attach+0x2c/0x38
> bus_add_driver+0xfc/0x1d0
> driver_register+0x64/0xf8
> __platform_driver_register+0x4c/0x58
> msm_drm_register+0x5c/0x60
> ...
>
> It turned out that clk_hw_get_parent_by_index() was returning NULL and
> we weren't checking. Let's check it so that we don't crash.
>
> Fixes: ac269395cdd8 ("clk: qcom: Convert to clk_hw based provider APIs")
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
> ---
> I haven't gone back and tried to reproduce this same crash on older
> kernels, but I'll put the blame on commit ac269395cdd8 ("clk: qcom:
> Convert to clk_hw based provider APIs"). Before that if we got a NULL
> parent back it was fine and dandy since a NULL "struct clk" is valid
> to use but a NULL "struct clk_hw" is not.
>
> Changes in v2:
> - Patch ("clk: qcom: rcg2: Don't crash...") new for v2.
>
> drivers/clk/qcom/clk-rcg2.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/clk/qcom/clk-rcg2.c b/drivers/clk/qcom/clk-rcg2.c
> index da045b200def..9098001ac805 100644
> --- a/drivers/clk/qcom/clk-rcg2.c
> +++ b/drivers/clk/qcom/clk-rcg2.c
> @@ -218,6 +218,9 @@ static int _freq_tbl_determine_rate(struct clk_hw *hw, const struct freq_tbl *f,
>
> clk_flags = clk_hw_get_flags(hw);
> p = clk_hw_get_parent_by_index(hw, index);
> + if (!p)
> + return -EINVAL;
> +
> if (clk_flags & CLK_SET_RATE_PARENT) {
> rate = f->freq;
> if (f->pre_div) {
Reviewed-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
