Re: [PATCH v2] clk: meson: change usleep_range() to udelay() for atomic context

[Jerome Brunet]

On Wed 05 Jul 2023 at 00:54, Dmitry Rokosov <ddrokosov@xxxxxxxxxxxxxx> wrote:

> The function meson_clk_pll_enable() can be invoked under the enable_lock
> spinlock from the clk core logic, which risks a kernel panic during the
> usleep_range() call:
>
>    BUG: scheduling while atomic: kworker/u4:2/36/0x00000002
>    Modules linked in: g_ffs usb_f_fs libcomposite
>    CPU: 1 PID: 36 Comm: kworker/u4:2 Not tainted 6.4.0-rc5 #273
>    Workqueue: events_unbound async_run_entry_fn
>    Call trace:
>     dump_backtrace+0x9c/0x128
>     show_stack+0x20/0x38
>     dump_stack_lvl+0x48/0x60
>     dump_stack+0x18/0x28
>     __schedule_bug+0x58/0x78
>     __schedule+0x828/0xa88
>     schedule+0x64/0xd8
>     schedule_hrtimeout_range_clock+0xd0/0x208
>     schedule_hrtimeout_range+0x1c/0x30
>     usleep_range_state+0x6c/0xa8
>     meson_clk_pll_enable+0x1f4/0x310
>     clk_core_enable+0x78/0x200
>     clk_core_enable+0x58/0x200
>     clk_core_enable+0x58/0x200
>     clk_core_enable+0x58/0x200
>     clk_enable+0x34/0x60
>
> So it is required to use the udelay() function instead of usleep_range()
> for the atomic context safety.
>
> Fixes: b6ec400aa153 ("clk: meson: introduce new pll power-on sequence for A1 SoC family")
> Reported-by: Jan Dakinevich <yvdakinevich@xxxxxxxxxxxxxx>
> Signed-off-by: Dmitry Rokosov <ddrokosov@xxxxxxxxxxxxxx>

Applied, Thx

> ---
> Changes v2 since v1 at [1]:
>     - remove redundant SoB from commit msg
>     - drop unuseful reference to clk_core_enable() from commit msg 
>
> Links:
>     [1] https://lore.kernel.org/all/20230703200404.20361-1-ddrokosov@xxxxxxxxxxxxxx/
> ---
>  drivers/clk/meson/clk-pll.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/clk/meson/clk-pll.c b/drivers/clk/meson/clk-pll.c
> index 56ec2210f1ad..eef6f37c8d8d 100644
> --- a/drivers/clk/meson/clk-pll.c
> +++ b/drivers/clk/meson/clk-pll.c
> @@ -367,9 +367,9 @@ static int meson_clk_pll_enable(struct clk_hw *hw)
>  	 * 3. enable the lock detect module
>  	 */
>  	if (MESON_PARM_APPLICABLE(&pll->current_en)) {
> -		usleep_range(10, 20);
> +		udelay(10);
>  		meson_parm_write(clk->map, &pll->current_en, 1);
> -		usleep_range(40, 50);
> +		udelay(40);
>  	};
>  
>  	if (MESON_PARM_APPLICABLE(&pll->l_detect)) {