Am Freitag, 10. März 2023, 14:08:15 CEST schrieb A. Sverdlin:
> From: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
>
> One of the reasons to do it is to save some CPU cycles on cpu_freq_get()
> under mutex. The second reason if the (false-positive) lockdep splat caused
> by the recursive feature of the "prepare_lock" (one clock instance is I2C
> peripheral clock and another is pcf85063 RTC as clock provider):
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 5.15.71+... #1 Tainted: G O
> ------------------------------------------------------
> fs-value/2332 is trying to acquire lock:
> ffff8000096cae08 (prepare_lock){+.+.}-{3:3}, at: clk_prepare_lock
>
> but task is already holding lock:
> ffff000011021100 (i2c_register_adapter){+.+.}-{3:3}, at:
> i2c_adapter_lock_bus
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #2 (i2c_register_adapter){+.+.}-{3:3}:
> lock_acquire
> rt_mutex_lock_nested
> i2c_adapter_lock_bus
> i2c_transfer
> regmap_i2c_read
> _regmap_raw_read
> _regmap_bus_read
> _regmap_read
> regmap_read
> pcf85063_probe
> i2c_device_probe
> really_probe
> __driver_probe_device
> driver_probe_device
> __device_attach_driver
> bus_for_each_drv
> __device_attach
> device_initial_probe
> bus_probe_device
> device_add
> device_register
> i2c_new_client_device
> of_i2c_register_devices
> i2c_register_adapter
> __i2c_add_numbered_adapter
> i2c_add_adapter
> lpi2c_imx_probe
> platform_probe
> really_probe
> __driver_probe_device
> driver_probe_device
> __device_attach_driver
> bus_for_each_drv
> __device_attach
> device_initial_probe
> bus_probe_device
> deferred_probe_work_func
> process_one_work
> worker_thread
> kthread
> ret_from_fork
>
> -> #1 (rtc_pcf85063:560:(&config->regmap)->lock){+.+.}-{3:3}:
> lock_acquire
> __mutex_lock
> mutex_lock_nested
> regmap_lock_mutex
> regmap_read
> pcf85063_clkout_recalc_rate
> __clk_register
> devm_clk_register
> pcf85063_probe
> i2c_device_probe
> really_probe
> __driver_probe_device
> driver_probe_device
> __device_attach_driver
> bus_for_each_drv
> __device_attach
> device_initial_probe
> bus_probe_device
> device_add
> device_register
> i2c_new_client_device
> of_i2c_register_devices
> i2c_register_adapter
> __i2c_add_numbered_adapter
> i2c_add_adapter
> lpi2c_imx_probe
> platform_probe
> really_probe
> __driver_probe_device
> driver_probe_device
> __device_attach_driver
> bus_for_each_drv
> __device_attach
> device_initial_probe
> bus_probe_device
> deferred_probe_work_func
> process_one_work
> worker_thread
> kthread
> ret_from_fork
>
> -> #0 (prepare_lock){+.+.}-{3:3}:
> __lock_acquire
> lock_acquire.part.0
> lock_acquire
> __mutex_lock
> mutex_lock_nested
> clk_prepare_lock
> clk_get_rate
> lpi2c_imx_xfer
> __i2c_transfer
> i2c_transfer
> regmap_i2c_read
> _regmap_raw_read
> regmap_raw_read
> regmap_bulk_read
> at24_read
> nvmem_reg_read
> bin_attr_nvmem_read
> sysfs_kf_bin_read
> kernfs_fop_read_iter
> new_sync_read
> vfs_read
> ksys_read
> __arm64_sys_read
> invoke_syscall
> ...
>
> other info that might help us debug this:
>
> Chain exists of:
> prepare_lock --> rtc_pcf85063:560:(&config->regmap)->lock -->
> i2c_register_adapter
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(i2c_register_adapter);
>
> lock(rtc_pcf85063:560:(&config->regmap)->lock); lock(i2c_register_adapter);
> lock(prepare_lock);
>
> *** DEADLOCK ***
>
> 4 locks held by .../2332:
> #0: ffff0000146eb288 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_read_iter
> #1: ffff000010fe4400 (kn->active#72){.+.+}-{0:0}, at: kernfs_fop_read_iter
> #2: ffff0000110168e8 (&at24->lock){+.+.}-{3:3}, at: at24_read
> #3: ffff000011021100 (i2c_register_adapter){+.+.}-{3:3}, at:
> i2c_adapter_lock_bus
>
> stack backtrace:
> CPU: 1 PID: 2332 Comm: ... Tainted: G O 5.15.71+... #1
> Hardware name: ... (DT)
> Call trace:
> dump_backtrace
> show_stack
> dump_stack_lvl
> dump_stack
> print_circular_bug
> check_noncircular
> __lock_acquire
> lock_acquire.part.0
> lock_acquire
> __mutex_lock
> mutex_lock_nested
> clk_prepare_lock
> clk_get_rate
> lpi2c_imx_xfer
> __i2c_transfer
> i2c_transfer
> regmap_i2c_read
> _regmap_raw_read
> regmap_raw_read
> regmap_bulk_read
> at24_read
> nvmem_reg_read
> bin_attr_nvmem_read
> sysfs_kf_bin_read
> kernfs_fop_read_iter
> new_sync_read
> vfs_read
> ksys_read
> __arm64_sys_read
> invoke_syscall
> ...
>
> Fixes: a55fa9d0e42e ("i2c: imx-lpi2c: add low power i2c bus driver")
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxxxx>
Reviewed-by: Alexander Stein <alexander.stein@xxxxxxxxxxxxxxx>
Note: [1] needs to be applied as well in order to get rid of all the lockdep
errors.
[1] https://lore.kernel.org/linux-i2c/20230424080627.20564-1-alexander.stein@xxxxxxxxxxxxxxx/T/#u
> ---
> drivers/i2c/busses/i2c-imx-lpi2c.c | 33 +++++++++++++++++++++++++++---
> 1 file changed, 30 insertions(+), 3 deletions(-)
>
> Changelog:
> v3: fixed build error reported by kernel test robot <lkp@xxxxxxxxx>
>
> https://lore.kernel.org/oe-kbuild-all/202303102010.pAv56wKs-lkp@xxxxxxxxx/
> v2: added clk_notifier as Alexander suggested
>
> diff --git a/drivers/i2c/busses/i2c-imx-lpi2c.c
> b/drivers/i2c/busses/i2c-imx-lpi2c.c index 188f2a36d2fd6..5f1d1d4e018bd
> 100644
> --- a/drivers/i2c/busses/i2c-imx-lpi2c.c
> +++ b/drivers/i2c/busses/i2c-imx-lpi2c.c
> @@ -100,6 +100,8 @@ struct lpi2c_imx_struct {
> __u8 *rx_buf;
> __u8 *tx_buf;
> struct completion complete;
> + struct notifier_block clk_change_nb;
> + unsigned int rate_per;
> unsigned int msglen;
> unsigned int delivered;
> unsigned int block_data;
> @@ -198,24 +200,37 @@ static void lpi2c_imx_stop(struct lpi2c_imx_struct
> *lpi2c_imx) } while (1);
> }
>
> +static int lpi2c_imx_clk_change_cb(struct notifier_block *nb,
> + unsigned long action, void *data)
> +{
> + struct clk_notifier_data *ndata = data;
> + struct lpi2c_imx_struct *lpi2c_imx = container_of(nb,
> + struct
lpi2c_imx_struct,
> +
clk_change_nb);
> +
> + if (action & POST_RATE_CHANGE)
> + lpi2c_imx->rate_per = ndata->new_rate;
> +
> + return NOTIFY_OK;
> +}
> +
> /* CLKLO = I2C_CLK_RATIO * CLKHI, SETHOLD = CLKHI, DATAVD = CLKHI/2 */
> static int lpi2c_imx_config(struct lpi2c_imx_struct *lpi2c_imx)
> {
> u8 prescale, filt, sethold, clkhi, clklo, datavd;
> - unsigned int clk_rate, clk_cycle;
> + unsigned int clk_cycle;
> enum lpi2c_imx_pincfg pincfg;
> unsigned int temp;
>
> lpi2c_imx_set_mode(lpi2c_imx);
>
> - clk_rate = clk_get_rate(lpi2c_imx->clks[0].clk);
> if (lpi2c_imx->mode == HS || lpi2c_imx->mode == ULTRA_FAST)
> filt = 0;
> else
> filt = 2;
>
> for (prescale = 0; prescale <= 7; prescale++) {
> - clk_cycle = clk_rate / ((1 << prescale) * lpi2c_imx-
>bitrate)
> + clk_cycle = lpi2c_imx->rate_per / ((1 << prescale) *
lpi2c_imx->bitrate)
> - 3 - (filt >> 1);
> clkhi = (clk_cycle + I2C_CLK_RATIO) / (I2C_CLK_RATIO + 1);
> clklo = clk_cycle - clkhi;
> @@ -588,6 +603,18 @@ static int lpi2c_imx_probe(struct platform_device
> *pdev) if (ret)
> return ret;
>
> + lpi2c_imx->clk_change_nb.notifier_call = lpi2c_imx_clk_change_cb;
> + ret = devm_clk_notifier_register(&pdev->dev, lpi2c_imx->clks[0].clk,
> + &lpi2c_imx->clk_change_nb);
> + if (ret)
> + return dev_err_probe(&pdev->dev, ret,
> + "can't register peripheral clock
notifier\n");
> + lpi2c_imx->rate_per = clk_get_rate(lpi2c_imx->clks[0].clk);
> + if (!lpi2c_imx->rate_per) {
> + dev_err(&pdev->dev, "can't get I2C peripheral clock
rate\n");
> + return -EINVAL;
> + }
> +
> pm_runtime_set_autosuspend_delay(&pdev->dev, I2C_PM_TIMEOUT);
> pm_runtime_use_autosuspend(&pdev->dev);
> pm_runtime_get_noresume(&pdev->dev);
--
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