qcom_slim_ngd_ctrl_probe: blocked on a mutex

qcom_slim_ngd_ctrl_probe: blocked on a mutex

[Tj]

Currently working on sdm850 device (Samsung Galaxy Book2 W737) and 
seeing kernel hang early and never recover when probing qcom-ngd-ctrl 
platform driver.  Only able to capture a photo of the stack traces as a 
result; I'll try to transcribe the important parts here. My diagnosis 
suggests that the module is calling __platform_driver_register() twice 
and may be the cause of the hang.

INFO: task swapper/0:1 is blocked on a mutex likely owned by task 
swapper/0:1
INFO: task swapper/0:1 blocked for more than 1232 seconds.
            Not tainted 7.0.0.-rc2-adm845 #80
task:swapper/0    state:D pid:1 tgid:1 ppid:0 task_flags:0x <-- not in photo
Call trace:
__switch_to_0x104/0x1c8 (T)
__schedule+0x438/0x1168
schedule+0x3c/0x120
schedule_preempt_disabled+0x2c/0x50
__mutex_lock.constprop.0+0x3d0/0x938
__mutex_lock_slowpath+0x1c/0x30
__driver_attach+0x38/0x280
bus_for_each_dev+0x80/0xc8
driver_attach+0x2c/0x40
bus_add_driver+0x128/0x258
driver_register+0x68/0x138
__platform_driver_register+0x2c/0x40
qcom_slim_ngd_ctrl_probe+0x1f4/0x400
platform_probe+0x64/0xa8
really_probe+0xc8/0x3f0
__driver_probe_device+0x88/0x190
driver_probe_device+0x44/0x120
__driver_attach+0x138/0x280
bus_for_each_dev+0x80/0xc8
driver_attach+0x2c/0x40
bus_add_driver+0x128/0x258
driver_register+0x68/0x138
__platform_driver_register+0x2c/0x40
qcom_slim_ngd_ctrl_driver_init+0x24/0x38
do_one_initcall+0x60/0x450
kernel_init_freeable+0x23c/0x630
kernel_init+0x2c/0x1f8
ret_from_fork+0x10/0x20

My analysis:

=drivers/slimbus/qcom-ngd-ctrl.c
module_platform_driver(qcom_slim_ngd_ctrl_driver);

   =include/linux/platform_device.h
   #define module_platform_driver(__platform_driver) \
   module_driver(__platform_driver, platform_driver_register, 
platform_driver_unregister)
     =include/device/driver.h
     /* Each module may only use this macro once */
     #define module_driver(__driver, __register, __unregister, ...) 
return __register(&(__driver) , ##__VA_ARGS__);
       // __register == platform_driver_register

     #define platform_driver_register(drv) 
__platform_driver_register(drv, THIS_MODULE)
       =drivers/base/platform.c
       __platform_driver_register(struct platform_driver *drv, struct 
module *owner)
         =drivers/base/driver.c
         driver_register(&drv->driver);
           bus_add_driver()
             driver_attach()
               bus_for_each_dev()
                 __dirver_attach()
                   driver_probe_device()
                     really_probe()
                       platform_probe()
                         =drivers/slimbus/qcom-ngd-ctrl.c
                         qcom_slim_ngd_ctrl_probe(struct platform_device 
*pdev)
platform_driver_register(&qcom_slim_ngd_driver);
                           // and round we go again!

Re: qcom_slim_ngd_ctrl_probe: blocked on a mutex

[Konrad Dybcio]

On 3/12/26 1:14 AM, Tj wrote:
> Currently working on sdm850 device (Samsung Galaxy Book2 W737) and 
> seeing kernel hang early and never recover when probing qcom-ngd-ctrl 
> platform driver.  Only able to capture a photo of the stack traces as a 
> result; I'll try to transcribe the important parts here. My diagnosis 
> suggests that the module is calling __platform_driver_register() twice 
> and may be the cause of the hang.

https://lore.kernel.org/all/20260309-slim-ngd-dev-v1-0-5843e3ed62a3@oss.qualcomm.com/

should be able to help with some of that

Konrad

Re: qcom_slim_ngd_ctrl_probe: blocked on a mutex

[Tj]

On 13/03/2026 09:54, Konrad Dybcio wrote:
> On 3/12/26 1:14 AM, Tj wrote:
>> Currently working on sdm850 device (Samsung Galaxy Book2 W737) and
>> seeing kernel hang early and never recover when probing qcom-ngd-ctrl
>> platform driver.  Only able to capture a photo of the stack traces as a
>> result; I'll try to transcribe the important parts here. My diagnosis
>> suggests that the module is calling __platform_driver_register() twice
>> and may be the cause of the hang.
> https://lore.kernel.org/all/20260309-slim-ngd-dev-v1-0-5843e3ed62a3@oss.qualcomm.com/
>
> should be able to help with some of that

Thank-you. This morning I'd just resolved the platform_driver_register 
issue myself so now seeing

qcom,slim-ngd-ctrl 171c0000.slim-ngd: SLIM SAT: Rcvd master capability
qcom,slim-ngd-ctrl 171c0000.slim-ngd: SLIM controller Registered

However the order of registration of the two drivers is important; ctrl 
should be last, so I'm surprised that Patch 1 works.

My local fix is:

     slimbus: ngd: fix lock hang on probe

     Module contains two platform_drivers. The initial probe calls
     platform_register_driver() with the second struct platform_driver.

     This caused a hung task due to mutex lock in __driver_attach():

     INFO: task swapper/0:1 blocked for more than 1232 seconds.
                Not tainted 7.0.0.-rc2-sdm845 #89
     task:swapper/0    state:D pid:1 tgid:1 ppid:0 task_flags:0x0140 
flags:0x00000010
     Call trace:
     __switch_to_0x104/0x1c8 (T)
     __schedule+0x438/0x1168
     schedule+0x3c/0x120
     schedule_preempt_disabled+0x2c/0x50
     __mutex_lock.constprop.0+0x3d0/0x938
     __mutex_lock_slowpath+0x1c/0x30
     __driver_attach+0x38/0x280
     bus_for_each_dev+0x80/0xc8
     driver_attach+0x2c/0x40
     bus_add_driver+0x128/0x258
     driver_register+0x68/0x138
     __platform_driver_register+0x2c/0x40
     qcom_slim_ngd_ctrl_probe+0x1f4/0x400
     platform_probe+0x64/0xa8
     really_probe+0xc8/0x3f0
     __driver_probe_device+0x88/0x190
     driver_probe_device+0x44/0x120
     __driver_attach+0x138/0x280
     bus_for_each_dev+0x80/0xc8
     driver_attach+0x2c/0x40
     bus_add_driver+0x128/0x258
     driver_register+0x68/0x138
     __platform_driver_register+0x2c/0x40
     qcom_slim_ngd_ctrl_driver_init+0x24/0x38
     do_one_initcall+0x60/0x450
     kernel_init_freeable+0x23c/0x630
     kernel_init+0x2c/0x1f8
     ret_from_fork+0x10/0x20
     INFO: task swapper/0:1 is blocked on a mutex likely owned by task
     swapper/0:1.

     Showing all locks held in the system:
     2 locks held by swapper/0/1:
      #0: ffff000080ff80f8 (&dev->mutex){....}-{4:4}, at:
          __driver_attach+0x19c/0x2c0
      #1: ffff000080ff80f8 (&dev->mutex){....}-{4:4}, at:
          __driver_attach+0x38/0x2c0
     1 lock held by khungtaskd/73:
      #0: ffffbc5dfc38f1d8 (rcu_read_lock){....}-{1:3}, at:
          debug_show_all_locks+0x18/0x1f0

     After this fix:

     qcom,slim-ngd-ctrl 171c0000.slim-ngd: SLIM SAT: Rcvd master capability
     qcom,slim-ngd-ctrl 171c0000.slim-ngd: SLIM controller Registered

diff --git a/drivers/slimbus/qcom-ngd-ctrl.c 
b/drivers/slimbus/qcom-ngd-ctrl.c
index 9aa7218b4e8d2..abdd4ad57f2d2 100644
--- a/drivers/slimbus/qcom-ngd-ctrl.c
+++ b/drivers/slimbus/qcom-ngd-ctrl.c
@@ -1664,7 +1664,6 @@ static int qcom_slim_ngd_ctrl_probe(struct 
platform_device *pdev)
                 goto err_pdr_lookup;
         }

-       platform_driver_register(&qcom_slim_ngd_driver);
         return of_qcom_slim_ngd_register(dev, ctrl);

  err_pdr_alloc:
@@ -1754,6 +1753,23 @@ static struct platform_driver 
qcom_slim_ngd_driver = {
         },
  };

-module_platform_driver(qcom_slim_ngd_ctrl_driver);
+static struct platform_driver * const qcom_slim_ngd_drivers[] = {
+       /* Order here is important; ctrl last */
+       &qcom_slim_ngd_driver,
+       &qcom_slim_ngd_ctrl_driver,
+};
+
+static int __init qcom_slim_ngd_init(void)
+{
+       return platform_register_drivers(qcom_slim_ngd_drivers, 
ARRAY_SIZE(qcom_slim_ngd_drivers));
+}
+module_init(qcom_slim_ngd_init);
+
+static void __exit qcom_slim_ngd_exit(void)
+{
+       return platform_unregister_drivers(qcom_slim_ngd_drivers, 
ARRAY_SIZE(qcom_slim_ngd_drivers));
+}
+module_exit(qcom_slim_ngd_exit);
+
  MODULE_LICENSE("GPL v2");
  MODULE_DESCRIPTION("Qualcomm SLIMBus NGD controller");

Re: qcom_slim_ngd_ctrl_probe: blocked on a mutex

[Konrad Dybcio]

On 3/13/26 1:00 PM, Tj wrote:
> On 13/03/2026 09:54, Konrad Dybcio wrote:
>> On 3/12/26 1:14 AM, Tj wrote:
>>> Currently working on sdm850 device (Samsung Galaxy Book2 W737) and
>>> seeing kernel hang early and never recover when probing qcom-ngd-ctrl
>>> platform driver.  Only able to capture a photo of the stack traces as a
>>> result; I'll try to transcribe the important parts here. My diagnosis
>>> suggests that the module is calling __platform_driver_register() twice
>>> and may be the cause of the hang.
>> https://lore.kernel.org/all/20260309-slim-ngd-dev-v1-0-5843e3ed62a3@oss.qualcomm.com/
>>
>> should be able to help with some of that
> 
> Thank-you. This morning I'd just resolved the platform_driver_register 
> issue myself so now seeing
> 
> qcom,slim-ngd-ctrl 171c0000.slim-ngd: SLIM SAT: Rcvd master capability
> qcom,slim-ngd-ctrl 171c0000.slim-ngd: SLIM controller Registered
> 
> However the order of registration of the two drivers is important; ctrl 
> should be last, so I'm surprised that Patch 1 works.

Please direct your findings to that thread.

Konrad