Hi Adrien,
On Sat, Feb 18, 2023 at 3:50 AM Adrien Thierry <athierry@xxxxxxxxxx> wrote:
>
> During ufs initialization, devfreq initialization is asynchronous:
> ufshcd_async_scan() calls ufshcd_add_lus(), which in turn initializes
> devfreq for ufs. The simple ondemand governor is then loaded. If it is
> built as a module, request_module() is called and throws a warning:
>
> WARNING: CPU: 7 PID: 167 at kernel/kmod.c:136 __request_module+0x1e0/0x460
> Modules linked in: crct10dif_ce llcc_qcom phy_qcom_qmp_usb ufs_qcom phy_qcom_snps_femto_v2 ufshcd_pltfrm phy_qcom_qmp_combo ufshcd_core phy_qcom_qmp_ufs qcom_wdt socinfo fuse ipv6
> CPU: 7 PID: 167 Comm: kworker/u16:3 Not tainted 6.2.0-rc6-00009-g58706f7fb045 #1
> Hardware name: Qualcomm SA8540P Ride (DT)
> Workqueue: events_unbound async_run_entry_fn
> pstate: 00400005 (nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> pc : __request_module+0x1e0/0x460
> lr : __request_module+0x1d8/0x460
> sp : ffff800009323b90
> x29: ffff800009323b90 x28: 0000000000000000 x27: 0000000000000000
> x26: ffff800009323d50 x25: ffff7b9045f57810 x24: ffff7b9045f57830
> x23: ffffdc5a83e426e8 x22: ffffdc5ae80a9818 x21: 0000000000000001
> x20: ffffdc5ae7502f98 x19: ffff7b9045f57800 x18: ffffffffffffffff
> x17: 312f716572667665 x16: 642f7366752e3030 x15: 0000000000000000
> x14: 000000000000021c x13: 0000000000005400 x12: ffff7b9042ed7614
> x11: ffff7b9042ed7600 x10: 00000000636c0890 x9 : 0000000000000038
> x8 : ffff7b9045f2c880 x7 : ffff7b9045f57c68 x6 : 0000000000000080
> x5 : 0000000000000000 x4 : 8000000000000000 x3 : 0000000000000000
> x2 : 0000000000000000 x1 : ffffdc5ae5d382f0 x0 : 0000000000000001
> Call trace:
> __request_module+0x1e0/0x460
> try_then_request_governor+0x7c/0x100
> devfreq_add_device+0x4b0/0x5fc
> ufshcd_async_scan+0x1d4/0x310 [ufshcd_core]
> async_run_entry_fn+0x34/0xe0
> process_one_work+0x1d0/0x320
> worker_thread+0x14c/0x444
> kthread+0x10c/0x110
> ret_from_fork+0x10/0x20
>
> This occurs because synchronous module loading from async is not
> allowed. According to __request_module():
>
> /*
> * We don't allow synchronous module loading from async. Module
> * init may invoke async_synchronize_full() which will end up
> * waiting for this task which already is waiting for the module
> * loading to complete, leading to a deadlock.
> */
>
> I experienced such a deadlock on the Qualcomm QDrive3/sa8540p-ride. With
> DEVFREQ_GOV_SIMPLE_ONDEMAND=m, the boot hangs after the warning.
>
> This patch fixes both the warning and the deadlock, by moving devfreq
> initialization out of the async routine.
>
> I tested this on the sa8540p-ride by using fio to put the UFS under
> load, and printing the trace generated by
> /sys/kernel/tracing/events/ufs/ufshcd_clk_scaling events. The trace
> looks similar with and without the change.
>
> Signed-off-by: Adrien Thierry <athierry@xxxxxxxxxx>
> ---
> v3: Addressed Bart's comments
> v2: Addressed Bart's comments
>
> drivers/ufs/core/ufshcd.c | 47 ++++++++++++++++++++++++++-------------
> include/ufs/ufshcd.h | 1 +
> 2 files changed, 32 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> index 3a1c4d31e010..2c22a1367440 100644
> --- a/drivers/ufs/core/ufshcd.c
> +++ b/drivers/ufs/core/ufshcd.c
> @@ -1357,6 +1357,13 @@ static int ufshcd_devfreq_target(struct device *dev,
> struct ufs_clk_info *clki;
> unsigned long irq_flags;
>
> + /*
> + * Skip devfreq if ufs initialization is not finished.
> + * Otherwise ufs could be in a inconsistent state.
> + */
> + if (!smp_load_acquire(&hba->logical_unit_scan_finished))
> + return 0;
> +
> if (!ufshcd_is_clkscaling_supported(hba))
> return -EINVAL;
>
> @@ -8136,22 +8143,6 @@ static int ufshcd_add_lus(struct ufs_hba *hba)
> if (ret)
> goto out;
>
> - /* Initialize devfreq after UFS device is detected */
> - if (ufshcd_is_clkscaling_supported(hba)) {
> - memcpy(&hba->clk_scaling.saved_pwr_info.info,
> - &hba->pwr_info,
> - sizeof(struct ufs_pa_layer_attr));
> - hba->clk_scaling.saved_pwr_info.is_valid = true;
> - hba->clk_scaling.is_allowed = true;
> -
> - ret = ufshcd_devfreq_init(hba);
> - if (ret)
> - goto out;
> -
> - hba->clk_scaling.is_enabled = true;
> - ufshcd_init_clk_scaling_sysfs(hba);
> - }
> -
> ufs_bsg_probe(hba);
> ufshpb_init(hba);
> scsi_scan_host(hba->host);
> @@ -8290,6 +8281,12 @@ static void ufshcd_async_scan(void *data, async_cookie_t cookie)
> if (ret) {
> pm_runtime_put_sync(hba->dev);
> ufshcd_hba_exit(hba);
> + } else {
> + /*
> + * Make sure that when reader code sees ufs initialization has finished,
> + * all initialization steps have really been executed.
> + */
> + smp_store_release(&hba->logical_unit_scan_finished, true);
> }
> }
>
> @@ -9896,12 +9893,30 @@ int ufshcd_init(struct ufs_hba *hba, void __iomem *mmio_base, unsigned int irq)
> */
> ufshcd_set_ufs_dev_active(hba);
>
> + /* Initialize devfreq */
> + if (ufshcd_is_clkscaling_supported(hba)) {
> + memcpy(&hba->clk_scaling.saved_pwr_info.info,
> + &hba->pwr_info,
> + sizeof(struct ufs_pa_layer_attr));
Here, hba->pwr_info is not initialized yet, so
hba->clk_scaling.saved_pwr_info will also have uninitialized values.
This is logically incorrect.
First of all, hba->saved_pwr_info is originally designed to keep the
"scaled-up" gear. This statement breaks it.
In addition, the incorrect hba->save_pwr_info may cause serious issues
in ufshcd_scale_gear(), as power mode changes will fail due to
incorrect "new_pwr_info".
Could you please revert this patch first and then upload a fixed one?
Thanks.
Stanley
