scsi: ufs: core: Initialize devfreq synchronously

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.
   */

Such a deadlock was experienced on the Qualcomm QDrive3/sa8540p-ride. With
DEVFREQ_GOV_SIMPLE_ONDEMAND=m, the boot hangs after the warning.

Fix both the warning and the deadlock by moving devfreq initialization out
of the async routine.

Tested 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.

Link: https://lore.kernel.org/r/20230217194423.42553-1-athierry@redhat.com
Signed-off-by: Adrien Thierry <athierry@redhat.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 3b3cf78..0baeec4 100644 (file)
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -1411,6 +1411,13 @@ 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;
 
@@ -8384,22 +8391,6 @@ 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);
@@ -8669,6 +8660,12 @@ out:
        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);
        }
 }
 
@@ -10309,12 +10306,30 @@ 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));
+               hba->clk_scaling.saved_pwr_info.is_valid = true;
+               hba->clk_scaling.is_allowed = true;
+
+               err = ufshcd_devfreq_init(hba);
+               if (err)
+                       goto rpm_put_sync;
+
+               hba->clk_scaling.is_enabled = true;
+               ufshcd_init_clk_scaling_sysfs(hba);
+       }
+
        async_schedule(ufshcd_async_scan, hba);
        ufs_sysfs_add_nodes(hba->dev);
 
        device_enable_async_suspend(dev);
        return 0;
 
+rpm_put_sync:
+       pm_runtime_put_sync(dev);
 free_tmf_queue:
        blk_mq_destroy_queue(hba->tmf_queue);
        blk_put_queue(hba->tmf_queue);

diff --git a/include/ufs/ufshcd.h b/include/ufs/ufshcd.h
index ed9e3d5..05e4164 100644 (file)
--- a/include/ufs/ufshcd.h
+++ b/include/ufs/ufshcd.h
@@ -978,6 +978,7 @@ struct ufs_hba {
        struct completion *uic_async_done;
 
        enum ufshcd_state ufshcd_state;
+       bool logical_unit_scan_finished;
        u32 eh_flags;
        u32 intr_mask;
        u16 ee_ctrl_mask;