The device object rescan in acpi_scan_clear_dep_fn is scheduled
in the system workqueue which is not guaranteed to be finished
before entering userspace. This will cause the problem that
some key devices are missed when the init task try to find them,
e.g. console devices and root devices (PCIe nvme, etc).
This issues is more possbile to happen on RISCV since these
devices using GSI interrupt may depend on APLIC and will be
scanned in acpi_scan_clear_dep_queue() after APLIC initialized.

Fix this by scheduling the acpi_scan_clear_dep_queue() using async
schedule function rather than the system workqueue. The deferred
works will be synchronized by async_synchronize_full() before
entering init task.

Update the comment as well.

Signed-off-by: Yicong Yang <yang.yicong@picoheart.com>
---
 drivers/acpi/scan.c | 35 ++++++++++++++++-------------------
 1 file changed, 16 insertions(+), 19 deletions(-)

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index 416d87f9bd10..bf0d8ba9ba19 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -5,6 +5,7 @@
 
 #define pr_fmt(fmt) "ACPI: " fmt
 
+#include <linux/async.h>
 #include <linux/module.h>
 #include <linux/init.h>
 #include <linux/slab.h>
@@ -2365,39 +2366,35 @@ struct acpi_scan_clear_dep_work {
 	struct acpi_device *adev;
 };
 
-static void acpi_scan_clear_dep_fn(struct work_struct *work)
+static void acpi_scan_clear_dep_fn(void *dev, async_cookie_t cookie)
 {
-	struct acpi_scan_clear_dep_work *cdw;
-
-	cdw = container_of(work, struct acpi_scan_clear_dep_work, work);
+	struct acpi_device *adev = to_acpi_device(dev);
 
 	acpi_scan_lock_acquire();
-	acpi_bus_attach(cdw->adev, (void *)true);
+	acpi_bus_attach(adev, (void *)true);
 	acpi_scan_lock_release();
 
-	acpi_dev_put(cdw->adev);
-	kfree(cdw);
+	acpi_dev_put(adev);
 }
 
 static bool acpi_scan_clear_dep_queue(struct acpi_device *adev)
 {
-	struct acpi_scan_clear_dep_work *cdw;
-
 	if (adev->dep_unmet)
 		return false;
 
-	cdw = kmalloc(sizeof(*cdw), GFP_KERNEL);
-	if (!cdw)
-		return false;
-
-	cdw->adev = adev;
-	INIT_WORK(&cdw->work, acpi_scan_clear_dep_fn);
 	/*
-	 * Since the work function may block on the lock until the entire
-	 * initial enumeration of devices is complete, put it into the unbound
-	 * workqueue.
+	 * Async schedule the deferred acpi_scan_clear_dep_fn() since:
+	 * - acpi_bus_attach() needs to hold acpi_scan_lock which cannot
+	 *   be acquired under acpi_dep_list_lock (held here)
+	 * - the deferred work at boot stage is ensured to be finished
+	 *   before entering init task by the async_synchronize_full()
+	 *   barrier
+	 *
+	 * Use _nocall variant since it'll return on failure instead of
+	 * run the function synchronously.
 	 */
-	queue_work(system_dfl_wq, &cdw->work);
+	if (!async_schedule_dev_nocall(acpi_scan_clear_dep_fn, &adev->dev))
+		return false;
 
 	return true;
 }
-- 
2.34.1

On Thu, Jan 22, 2026 at 8:35 AM Yicong Yang <yang.yicong@picoheart.com> wrote:
>
> The device object rescan in acpi_scan_clear_dep_fn is scheduled
> in the system workqueue which is not guaranteed to be finished
> before entering userspace. This will cause the problem that
> some key devices are missed when the init task try to find them,
> e.g. console devices and root devices (PCIe nvme, etc).
> This issues is more possbile to happen on RISCV since these
> devices using GSI interrupt may depend on APLIC and will be
> scanned in acpi_scan_clear_dep_queue() after APLIC initialized.
>
> Fix this by scheduling the acpi_scan_clear_dep_queue() using async
> schedule function rather than the system workqueue. The deferred
> works will be synchronized by async_synchronize_full() before
> entering init task.
>
> Update the comment as well.
>
> Signed-off-by: Yicong Yang <yang.yicong@picoheart.com>
> ---
>  drivers/acpi/scan.c | 35 ++++++++++++++++-------------------
>  1 file changed, 16 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index 416d87f9bd10..bf0d8ba9ba19 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -5,6 +5,7 @@
>
>  #define pr_fmt(fmt) "ACPI: " fmt
>
> +#include <linux/async.h>
>  #include <linux/module.h>
>  #include <linux/init.h>
>  #include <linux/slab.h>
> @@ -2365,39 +2366,35 @@ struct acpi_scan_clear_dep_work {
>         struct acpi_device *adev;
>  };
>
> -static void acpi_scan_clear_dep_fn(struct work_struct *work)
> +static void acpi_scan_clear_dep_fn(void *dev, async_cookie_t cookie)
>  {
> -       struct acpi_scan_clear_dep_work *cdw;
> -
> -       cdw = container_of(work, struct acpi_scan_clear_dep_work, work);
> +       struct acpi_device *adev = to_acpi_device(dev);
>
>         acpi_scan_lock_acquire();
> -       acpi_bus_attach(cdw->adev, (void *)true);
> +       acpi_bus_attach(adev, (void *)true);
>         acpi_scan_lock_release();
>
> -       acpi_dev_put(cdw->adev);
> -       kfree(cdw);
> +       acpi_dev_put(adev);
>  }
>
>  static bool acpi_scan_clear_dep_queue(struct acpi_device *adev)
>  {
> -       struct acpi_scan_clear_dep_work *cdw;
> -
>         if (adev->dep_unmet)
>                 return false;
>
> -       cdw = kmalloc(sizeof(*cdw), GFP_KERNEL);
> -       if (!cdw)
> -               return false;
> -
> -       cdw->adev = adev;
> -       INIT_WORK(&cdw->work, acpi_scan_clear_dep_fn);
>         /*
> -        * Since the work function may block on the lock until the entire
> -        * initial enumeration of devices is complete, put it into the unbound
> -        * workqueue.
> +        * Async schedule the deferred acpi_scan_clear_dep_fn() since:
> +        * - acpi_bus_attach() needs to hold acpi_scan_lock which cannot
> +        *   be acquired under acpi_dep_list_lock (held here)
> +        * - the deferred work at boot stage is ensured to be finished
> +        *   before entering init task by the async_synchronize_full()
> +        *   barrier
> +        *
> +        * Use _nocall variant since it'll return on failure instead of
> +        * run the function synchronously.
>          */
> -       queue_work(system_dfl_wq, &cdw->work);
> +       if (!async_schedule_dev_nocall(acpi_scan_clear_dep_fn, &adev->dev))

If the problem is that system_dfl_wq is too slow, why don't you just
try a dedicated workqueue for this?

There's no need to modify all of this code.

> +               return false;
>
>         return true;
>  }
> --

On 1/22/26 7:19 PM, Rafael J. Wysocki wrote:
> On Thu, Jan 22, 2026 at 8:35 AM Yicong Yang <yang.yicong@picoheart.com> wrote:
>>
>> The device object rescan in acpi_scan_clear_dep_fn is scheduled
>> in the system workqueue which is not guaranteed to be finished
>> before entering userspace. This will cause the problem that
>> some key devices are missed when the init task try to find them,
>> e.g. console devices and root devices (PCIe nvme, etc).
>> This issues is more possbile to happen on RISCV since these
>> devices using GSI interrupt may depend on APLIC and will be
>> scanned in acpi_scan_clear_dep_queue() after APLIC initialized.
>>
>> Fix this by scheduling the acpi_scan_clear_dep_queue() using async
>> schedule function rather than the system workqueue. The deferred
>> works will be synchronized by async_synchronize_full() before
>> entering init task.
>>
>> Update the comment as well.
>>
>> Signed-off-by: Yicong Yang <yang.yicong@picoheart.com>
>> ---
>>  drivers/acpi/scan.c | 35 ++++++++++++++++-------------------
>>  1 file changed, 16 insertions(+), 19 deletions(-)
>>
>> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
>> index 416d87f9bd10..bf0d8ba9ba19 100644
>> --- a/drivers/acpi/scan.c
>> +++ b/drivers/acpi/scan.c
>> @@ -5,6 +5,7 @@
>>
>>  #define pr_fmt(fmt) "ACPI: " fmt
>>
>> +#include <linux/async.h>
>>  #include <linux/module.h>
>>  #include <linux/init.h>
>>  #include <linux/slab.h>
>> @@ -2365,39 +2366,35 @@ struct acpi_scan_clear_dep_work {
>>         struct acpi_device *adev;
>>  };
>>
>> -static void acpi_scan_clear_dep_fn(struct work_struct *work)
>> +static void acpi_scan_clear_dep_fn(void *dev, async_cookie_t cookie)
>>  {
>> -       struct acpi_scan_clear_dep_work *cdw;
>> -
>> -       cdw = container_of(work, struct acpi_scan_clear_dep_work, work);
>> +       struct acpi_device *adev = to_acpi_device(dev);
>>
>>         acpi_scan_lock_acquire();
>> -       acpi_bus_attach(cdw->adev, (void *)true);
>> +       acpi_bus_attach(adev, (void *)true);
>>         acpi_scan_lock_release();
>>
>> -       acpi_dev_put(cdw->adev);
>> -       kfree(cdw);
>> +       acpi_dev_put(adev);
>>  }
>>
>>  static bool acpi_scan_clear_dep_queue(struct acpi_device *adev)
>>  {
>> -       struct acpi_scan_clear_dep_work *cdw;
>> -
>>         if (adev->dep_unmet)
>>                 return false;
>>
>> -       cdw = kmalloc(sizeof(*cdw), GFP_KERNEL);
>> -       if (!cdw)
>> -               return false;
>> -
>> -       cdw->adev = adev;
>> -       INIT_WORK(&cdw->work, acpi_scan_clear_dep_fn);
>>         /*
>> -        * Since the work function may block on the lock until the entire
>> -        * initial enumeration of devices is complete, put it into the unbound
>> -        * workqueue.
>> +        * Async schedule the deferred acpi_scan_clear_dep_fn() since:
>> +        * - acpi_bus_attach() needs to hold acpi_scan_lock which cannot
>> +        *   be acquired under acpi_dep_list_lock (held here)
>> +        * - the deferred work at boot stage is ensured to be finished
>> +        *   before entering init task by the async_synchronize_full()
>> +        *   barrier
>> +        *
>> +        * Use _nocall variant since it'll return on failure instead of
>> +        * run the function synchronously.
>>          */
>> -       queue_work(system_dfl_wq, &cdw->work);
>> +       if (!async_schedule_dev_nocall(acpi_scan_clear_dep_fn, &adev->dev))
> 
> If the problem is that system_dfl_wq is too slow, why don't you just
> try a dedicated workqueue for this?
> 
> There's no need to modify all of this code.
> 

The problem is that these works are not finished before entering userspace,
so some key devices like console or PCIe nvme (for root device) is not ready
in time userspace init running.

If we use a dedicated workqueue we still need to do the synchronization
somewhere before entering the userspace to solve the problem. But that's just
what async_schedule* does: queue the function in async_wq (also an unbound one)
and wait finish before execute init process by async_synchronize_full(). Does
it make sense?

Thanks.

On Thu, Jan 22, 2026 at 1:50 PM Yicong Yang <yang.yicong@picoheart.com> wrote:
>
> On 1/22/26 7:19 PM, Rafael J. Wysocki wrote:
> > On Thu, Jan 22, 2026 at 8:35 AM Yicong Yang <yang.yicong@picoheart.com> wrote:
> >>
> >> The device object rescan in acpi_scan_clear_dep_fn is scheduled
> >> in the system workqueue which is not guaranteed to be finished
> >> before entering userspace. This will cause the problem that
> >> some key devices are missed when the init task try to find them,
> >> e.g. console devices and root devices (PCIe nvme, etc).
> >> This issues is more possbile to happen on RISCV since these
> >> devices using GSI interrupt may depend on APLIC and will be
> >> scanned in acpi_scan_clear_dep_queue() after APLIC initialized.
> >>
> >> Fix this by scheduling the acpi_scan_clear_dep_queue() using async
> >> schedule function rather than the system workqueue. The deferred
> >> works will be synchronized by async_synchronize_full() before
> >> entering init task.
> >>
> >> Update the comment as well.
> >>
> >> Signed-off-by: Yicong Yang <yang.yicong@picoheart.com>
> >> ---
> >>  drivers/acpi/scan.c | 35 ++++++++++++++++-------------------
> >>  1 file changed, 16 insertions(+), 19 deletions(-)
> >>
> >> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> >> index 416d87f9bd10..bf0d8ba9ba19 100644
> >> --- a/drivers/acpi/scan.c
> >> +++ b/drivers/acpi/scan.c
> >> @@ -5,6 +5,7 @@
> >>
> >>  #define pr_fmt(fmt) "ACPI: " fmt
> >>
> >> +#include <linux/async.h>
> >>  #include <linux/module.h>
> >>  #include <linux/init.h>
> >>  #include <linux/slab.h>
> >> @@ -2365,39 +2366,35 @@ struct acpi_scan_clear_dep_work {
> >>         struct acpi_device *adev;
> >>  };
> >>
> >> -static void acpi_scan_clear_dep_fn(struct work_struct *work)
> >> +static void acpi_scan_clear_dep_fn(void *dev, async_cookie_t cookie)
> >>  {
> >> -       struct acpi_scan_clear_dep_work *cdw;
> >> -
> >> -       cdw = container_of(work, struct acpi_scan_clear_dep_work, work);
> >> +       struct acpi_device *adev = to_acpi_device(dev);
> >>
> >>         acpi_scan_lock_acquire();
> >> -       acpi_bus_attach(cdw->adev, (void *)true);
> >> +       acpi_bus_attach(adev, (void *)true);
> >>         acpi_scan_lock_release();
> >>
> >> -       acpi_dev_put(cdw->adev);
> >> -       kfree(cdw);
> >> +       acpi_dev_put(adev);
> >>  }
> >>
> >>  static bool acpi_scan_clear_dep_queue(struct acpi_device *adev)
> >>  {
> >> -       struct acpi_scan_clear_dep_work *cdw;
> >> -
> >>         if (adev->dep_unmet)
> >>                 return false;
> >>
> >> -       cdw = kmalloc(sizeof(*cdw), GFP_KERNEL);
> >> -       if (!cdw)
> >> -               return false;
> >> -
> >> -       cdw->adev = adev;
> >> -       INIT_WORK(&cdw->work, acpi_scan_clear_dep_fn);
> >>         /*
> >> -        * Since the work function may block on the lock until the entire
> >> -        * initial enumeration of devices is complete, put it into the unbound
> >> -        * workqueue.
> >> +        * Async schedule the deferred acpi_scan_clear_dep_fn() since:
> >> +        * - acpi_bus_attach() needs to hold acpi_scan_lock which cannot
> >> +        *   be acquired under acpi_dep_list_lock (held here)
> >> +        * - the deferred work at boot stage is ensured to be finished
> >> +        *   before entering init task by the async_synchronize_full()
> >> +        *   barrier
> >> +        *
> >> +        * Use _nocall variant since it'll return on failure instead of
> >> +        * run the function synchronously.
> >>          */
> >> -       queue_work(system_dfl_wq, &cdw->work);
> >> +       if (!async_schedule_dev_nocall(acpi_scan_clear_dep_fn, &adev->dev))
> >
> > If the problem is that system_dfl_wq is too slow, why don't you just
> > try a dedicated workqueue for this?
> >
> > There's no need to modify all of this code.
> >
>
> The problem is that these works are not finished before entering userspace,
> so some key devices like console or PCIe nvme (for root device) is not ready
> in time userspace init running.
>
> If we use a dedicated workqueue we still need to do the synchronization
> somewhere before entering the userspace to solve the problem. But that's just
> what async_schedule* does: queue the function in async_wq (also an unbound one)
> and wait finish before execute init process by async_synchronize_full(). Does
> it make sense?

Well, please see my reply to the other message.

On Thu, Jan 22, 2026 at 03:34:45PM +0800, Yicong Yang wrote:
> The device object rescan in acpi_scan_clear_dep_fn is scheduled
> in the system workqueue which is not guaranteed to be finished
> before entering userspace. This will cause the problem that
> some key devices are missed when the init task try to find them,
> e.g. console devices and root devices (PCIe nvme, etc).
> This issues is more possbile to happen on RISCV since these
> devices using GSI interrupt may depend on APLIC and will be
> scanned in acpi_scan_clear_dep_queue() after APLIC initialized.
> 
> Fix this by scheduling the acpi_scan_clear_dep_queue() using async
> schedule function rather than the system workqueue. The deferred
> works will be synchronized by async_synchronize_full() before
> entering init task.
> 
> Update the comment as well.
> 
> Signed-off-by: Yicong Yang <yang.yicong@picoheart.com>
> ---
>  drivers/acpi/scan.c | 35 ++++++++++++++++-------------------
>  1 file changed, 16 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index 416d87f9bd10..bf0d8ba9ba19 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -5,6 +5,7 @@
>  
>  #define pr_fmt(fmt) "ACPI: " fmt
>  
> +#include <linux/async.h>
>  #include <linux/module.h>
>  #include <linux/init.h>
>  #include <linux/slab.h>
> @@ -2365,39 +2366,35 @@ struct acpi_scan_clear_dep_work {
>  	struct acpi_device *adev;
>  };
>  
> -static void acpi_scan_clear_dep_fn(struct work_struct *work)
> +static void acpi_scan_clear_dep_fn(void *dev, async_cookie_t cookie)
>  {
> -	struct acpi_scan_clear_dep_work *cdw;
> -
> -	cdw = container_of(work, struct acpi_scan_clear_dep_work, work);
> +	struct acpi_device *adev = to_acpi_device(dev);
>  
>  	acpi_scan_lock_acquire();
> -	acpi_bus_attach(cdw->adev, (void *)true);
> +	acpi_bus_attach(adev, (void *)true);
>  	acpi_scan_lock_release();
>  
> -	acpi_dev_put(cdw->adev);
> -	kfree(cdw);
> +	acpi_dev_put(adev);
>  }
>  
>  static bool acpi_scan_clear_dep_queue(struct acpi_device *adev)
>  {
> -	struct acpi_scan_clear_dep_work *cdw;
> -
>  	if (adev->dep_unmet)
>  		return false;
>  
> -	cdw = kmalloc(sizeof(*cdw), GFP_KERNEL);
> -	if (!cdw)
> -		return false;
> -
> -	cdw->adev = adev;
> -	INIT_WORK(&cdw->work, acpi_scan_clear_dep_fn);
>  	/*
> -	 * Since the work function may block on the lock until the entire
> -	 * initial enumeration of devices is complete, put it into the unbound
> -	 * workqueue.
> +	 * Async schedule the deferred acpi_scan_clear_dep_fn() since:
> +	 * - acpi_bus_attach() needs to hold acpi_scan_lock which cannot
> +	 *   be acquired under acpi_dep_list_lock (held here)
> +	 * - the deferred work at boot stage is ensured to be finished
> +	 *   before entering init task by the async_synchronize_full()
> +	 *   barrier
> +	 *
> +	 * Use _nocall variant since it'll return on failure instead of
> +	 * run the function synchronously.
>  	 */
> -	queue_work(system_dfl_wq, &cdw->work);
> +	if (!async_schedule_dev_nocall(acpi_scan_clear_dep_fn, &adev->dev))
> +		return false;

This really feels wrong to me, you are taking a code path that has been
working for quite a while and changing it.  Perhaps your system ACPI
tables are the thing that is incorrect here?

What exactly is the problem that you are seeing?  Why not start with
that and then we can work out how to solve that issue?

thanks,

greg k-h

On 1/22/26 6:29 PM, Greg KH wrote:
> On Thu, Jan 22, 2026 at 03:34:45PM +0800, Yicong Yang wrote:
>> The device object rescan in acpi_scan_clear_dep_fn is scheduled
>> in the system workqueue which is not guaranteed to be finished
>> before entering userspace. This will cause the problem that
>> some key devices are missed when the init task try to find them,
>> e.g. console devices and root devices (PCIe nvme, etc).
>> This issues is more possbile to happen on RISCV since these
>> devices using GSI interrupt may depend on APLIC and will be
>> scanned in acpi_scan_clear_dep_queue() after APLIC initialized.
>>
>> Fix this by scheduling the acpi_scan_clear_dep_queue() using async
>> schedule function rather than the system workqueue. The deferred
>> works will be synchronized by async_synchronize_full() before
>> entering init task.
>>
>> Update the comment as well.
>>
>> Signed-off-by: Yicong Yang <yang.yicong@picoheart.com>
>> ---
>>  drivers/acpi/scan.c | 35 ++++++++++++++++-------------------
>>  1 file changed, 16 insertions(+), 19 deletions(-)
>>
>> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
>> index 416d87f9bd10..bf0d8ba9ba19 100644
>> --- a/drivers/acpi/scan.c
>> +++ b/drivers/acpi/scan.c
>> @@ -5,6 +5,7 @@
>>  
>>  #define pr_fmt(fmt) "ACPI: " fmt
>>  
>> +#include <linux/async.h>
>>  #include <linux/module.h>
>>  #include <linux/init.h>
>>  #include <linux/slab.h>
>> @@ -2365,39 +2366,35 @@ struct acpi_scan_clear_dep_work {
>>  	struct acpi_device *adev;
>>  };
>>  
>> -static void acpi_scan_clear_dep_fn(struct work_struct *work)
>> +static void acpi_scan_clear_dep_fn(void *dev, async_cookie_t cookie)
>>  {
>> -	struct acpi_scan_clear_dep_work *cdw;
>> -
>> -	cdw = container_of(work, struct acpi_scan_clear_dep_work, work);
>> +	struct acpi_device *adev = to_acpi_device(dev);
>>  
>>  	acpi_scan_lock_acquire();
>> -	acpi_bus_attach(cdw->adev, (void *)true);
>> +	acpi_bus_attach(adev, (void *)true);
>>  	acpi_scan_lock_release();
>>  
>> -	acpi_dev_put(cdw->adev);
>> -	kfree(cdw);
>> +	acpi_dev_put(adev);
>>  }
>>  
>>  static bool acpi_scan_clear_dep_queue(struct acpi_device *adev)
>>  {
>> -	struct acpi_scan_clear_dep_work *cdw;
>> -
>>  	if (adev->dep_unmet)
>>  		return false;
>>  
>> -	cdw = kmalloc(sizeof(*cdw), GFP_KERNEL);
>> -	if (!cdw)
>> -		return false;
>> -
>> -	cdw->adev = adev;
>> -	INIT_WORK(&cdw->work, acpi_scan_clear_dep_fn);
>>  	/*
>> -	 * Since the work function may block on the lock until the entire
>> -	 * initial enumeration of devices is complete, put it into the unbound
>> -	 * workqueue.
>> +	 * Async schedule the deferred acpi_scan_clear_dep_fn() since:
>> +	 * - acpi_bus_attach() needs to hold acpi_scan_lock which cannot
>> +	 *   be acquired under acpi_dep_list_lock (held here)
>> +	 * - the deferred work at boot stage is ensured to be finished
>> +	 *   before entering init task by the async_synchronize_full()
>> +	 *   barrier
>> +	 *
>> +	 * Use _nocall variant since it'll return on failure instead of
>> +	 * run the function synchronously.
>>  	 */
>> -	queue_work(system_dfl_wq, &cdw->work);
>> +	if (!async_schedule_dev_nocall(acpi_scan_clear_dep_fn, &adev->dev))
>> +		return false;
> 
> This really feels wrong to me, you are taking a code path that has been
> working for quite a while and changing it.  Perhaps your system ACPI
> tables are the thing that is incorrect here?
> 
> What exactly is the problem that you are seeing?  Why not start with
> that and then we can work out how to solve that issue?
> 

two issues here we met (as briefly mentioned in the commit and cover letter):
1. kernel panic due to userspace init cannot have an opened console. the
   console device scanning is queued in the system_dfl_wq in above code
   and not finished by the time userspace init process running, thus by
   the time userspace init running, no console is created
2. entering rescue shell due to no root devices (PCIe nvme in our case)
   found. same reason as above, the PCIe host bridge scanning is queued
   in above and finished after init process running.

The reason why these devices are created here is because they both depend
on riscv-aplic irqchip to serve their interrupts (console's wired
interrupt and PCI's INTx interrupts) and in order to keep the dependency
these devices are scanned and created after riscv-aplic initialized. The
riscv-aplic is initialized in device_initcall and invoke above codes for
the scan/creation of these devices, it's close to the time running
userspace init process. Since system_dfl_wq is used here and no synchronized
mechanism, the issues will happen if userspace init runs before these devices
are ready.

Previous solution [1] is to advance the initialization of riscv-aplic
earlier but the order still cannot be guaranteed conceptually.
With async_schedule_dev_nocal() the work queued is finished
before entering userspace init since we'll wait for completion at
async_synchronize_full() before executing userspace init process.

To solve the issue I think we should make these devices ready before
entering userspace and async schedule is one way to make it. It's also
using an unbound workqueue but have additional synchronization. Any
corrections or suggestions?

[1] https://lore.kernel.org/linux-riscv/20260114063730.78009-1-yang.yicong@picoheart.com/

Thanks.

On Thu, Jan 22, 2026 at 1:43 PM Yicong Yang <yang.yicong@picoheart.com> wrote:
>
> On 1/22/26 6:29 PM, Greg KH wrote:
> > On Thu, Jan 22, 2026 at 03:34:45PM +0800, Yicong Yang wrote:
> >> The device object rescan in acpi_scan_clear_dep_fn is scheduled
> >> in the system workqueue which is not guaranteed to be finished
> >> before entering userspace. This will cause the problem that
> >> some key devices are missed when the init task try to find them,
> >> e.g. console devices and root devices (PCIe nvme, etc).
> >> This issues is more possbile to happen on RISCV since these
> >> devices using GSI interrupt may depend on APLIC and will be
> >> scanned in acpi_scan_clear_dep_queue() after APLIC initialized.
> >>
> >> Fix this by scheduling the acpi_scan_clear_dep_queue() using async
> >> schedule function rather than the system workqueue. The deferred
> >> works will be synchronized by async_synchronize_full() before
> >> entering init task.
> >>
> >> Update the comment as well.
> >>
> >> Signed-off-by: Yicong Yang <yang.yicong@picoheart.com>
> >> ---
> >>  drivers/acpi/scan.c | 35 ++++++++++++++++-------------------
> >>  1 file changed, 16 insertions(+), 19 deletions(-)
> >>
> >> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> >> index 416d87f9bd10..bf0d8ba9ba19 100644
> >> --- a/drivers/acpi/scan.c
> >> +++ b/drivers/acpi/scan.c
> >> @@ -5,6 +5,7 @@
> >>
> >>  #define pr_fmt(fmt) "ACPI: " fmt
> >>
> >> +#include <linux/async.h>
> >>  #include <linux/module.h>
> >>  #include <linux/init.h>
> >>  #include <linux/slab.h>
> >> @@ -2365,39 +2366,35 @@ struct acpi_scan_clear_dep_work {
> >>      struct acpi_device *adev;
> >>  };
> >>
> >> -static void acpi_scan_clear_dep_fn(struct work_struct *work)
> >> +static void acpi_scan_clear_dep_fn(void *dev, async_cookie_t cookie)
> >>  {
> >> -    struct acpi_scan_clear_dep_work *cdw;
> >> -
> >> -    cdw = container_of(work, struct acpi_scan_clear_dep_work, work);
> >> +    struct acpi_device *adev = to_acpi_device(dev);
> >>
> >>      acpi_scan_lock_acquire();
> >> -    acpi_bus_attach(cdw->adev, (void *)true);
> >> +    acpi_bus_attach(adev, (void *)true);
> >>      acpi_scan_lock_release();
> >>
> >> -    acpi_dev_put(cdw->adev);
> >> -    kfree(cdw);
> >> +    acpi_dev_put(adev);
> >>  }
> >>
> >>  static bool acpi_scan_clear_dep_queue(struct acpi_device *adev)
> >>  {
> >> -    struct acpi_scan_clear_dep_work *cdw;
> >> -
> >>      if (adev->dep_unmet)
> >>              return false;
> >>
> >> -    cdw = kmalloc(sizeof(*cdw), GFP_KERNEL);
> >> -    if (!cdw)
> >> -            return false;
> >> -
> >> -    cdw->adev = adev;
> >> -    INIT_WORK(&cdw->work, acpi_scan_clear_dep_fn);
> >>      /*
> >> -     * Since the work function may block on the lock until the entire
> >> -     * initial enumeration of devices is complete, put it into the unbound
> >> -     * workqueue.
> >> +     * Async schedule the deferred acpi_scan_clear_dep_fn() since:
> >> +     * - acpi_bus_attach() needs to hold acpi_scan_lock which cannot
> >> +     *   be acquired under acpi_dep_list_lock (held here)
> >> +     * - the deferred work at boot stage is ensured to be finished
> >> +     *   before entering init task by the async_synchronize_full()
> >> +     *   barrier
> >> +     *
> >> +     * Use _nocall variant since it'll return on failure instead of
> >> +     * run the function synchronously.
> >>       */
> >> -    queue_work(system_dfl_wq, &cdw->work);
> >> +    if (!async_schedule_dev_nocall(acpi_scan_clear_dep_fn, &adev->dev))
> >> +            return false;
> >
> > This really feels wrong to me, you are taking a code path that has been
> > working for quite a while and changing it.  Perhaps your system ACPI
> > tables are the thing that is incorrect here?
> >
> > What exactly is the problem that you are seeing?  Why not start with
> > that and then we can work out how to solve that issue?
> >
>
> two issues here we met (as briefly mentioned in the commit and cover letter):
> 1. kernel panic due to userspace init cannot have an opened console. the
>    console device scanning is queued in the system_dfl_wq in above code
>    and not finished by the time userspace init process running, thus by
>    the time userspace init running, no console is created
> 2. entering rescue shell due to no root devices (PCIe nvme in our case)
>    found. same reason as above, the PCIe host bridge scanning is queued
>    in above and finished after init process running.
>
> The reason why these devices are created here is because they both depend
> on riscv-aplic irqchip to serve their interrupts (console's wired
> interrupt and PCI's INTx interrupts) and in order to keep the dependency
> these devices are scanned and created after riscv-aplic initialized. The
> riscv-aplic is initialized in device_initcall and invoke above codes for
> the scan/creation of these devices, it's close to the time running
> userspace init process. Since system_dfl_wq is used here and no synchronized
> mechanism, the issues will happen if userspace init runs before these devices
> are ready.

Well, there is flush_workqueue(), isn't it there?

> Previous solution [1] is to advance the initialization of riscv-aplic
> earlier but the order still cannot be guaranteed conceptually.
> With async_schedule_dev_nocal() the work queued is finished
> before entering userspace init since we'll wait for completion at
> async_synchronize_full() before executing userspace init process.
>
> To solve the issue I think we should make these devices ready before
> entering userspace and async schedule is one way to make it. It's also
> using an unbound workqueue but have additional synchronization. Any
> corrections or suggestions?

You can flush the dedicated workqueue at the same spot where you do
async_synchronize_full(), can't you?

> [1] https://lore.kernel.org/linux-riscv/20260114063730.78009-1-yang.yicong@picoheart.com/

On 1/22/26 9:21 PM, Rafael J. Wysocki wrote:
> On Thu, Jan 22, 2026 at 1:43 PM Yicong Yang <yang.yicong@picoheart.com> wrote:
>>
>> On 1/22/26 6:29 PM, Greg KH wrote:
>>> On Thu, Jan 22, 2026 at 03:34:45PM +0800, Yicong Yang wrote:
>>>> The device object rescan in acpi_scan_clear_dep_fn is scheduled
>>>> in the system workqueue which is not guaranteed to be finished
>>>> before entering userspace. This will cause the problem that
>>>> some key devices are missed when the init task try to find them,
>>>> e.g. console devices and root devices (PCIe nvme, etc).
>>>> This issues is more possbile to happen on RISCV since these
>>>> devices using GSI interrupt may depend on APLIC and will be
>>>> scanned in acpi_scan_clear_dep_queue() after APLIC initialized.
>>>>
>>>> Fix this by scheduling the acpi_scan_clear_dep_queue() using async
>>>> schedule function rather than the system workqueue. The deferred
>>>> works will be synchronized by async_synchronize_full() before
>>>> entering init task.
>>>>
>>>> Update the comment as well.
>>>>
>>>> Signed-off-by: Yicong Yang <yang.yicong@picoheart.com>
>>>> ---
>>>>  drivers/acpi/scan.c | 35 ++++++++++++++++-------------------
>>>>  1 file changed, 16 insertions(+), 19 deletions(-)
>>>>
>>>> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
>>>> index 416d87f9bd10..bf0d8ba9ba19 100644
>>>> --- a/drivers/acpi/scan.c
>>>> +++ b/drivers/acpi/scan.c
>>>> @@ -5,6 +5,7 @@
>>>>
>>>>  #define pr_fmt(fmt) "ACPI: " fmt
>>>>
>>>> +#include <linux/async.h>
>>>>  #include <linux/module.h>
>>>>  #include <linux/init.h>
>>>>  #include <linux/slab.h>
>>>> @@ -2365,39 +2366,35 @@ struct acpi_scan_clear_dep_work {
>>>>      struct acpi_device *adev;
>>>>  };
>>>>
>>>> -static void acpi_scan_clear_dep_fn(struct work_struct *work)
>>>> +static void acpi_scan_clear_dep_fn(void *dev, async_cookie_t cookie)
>>>>  {
>>>> -    struct acpi_scan_clear_dep_work *cdw;
>>>> -
>>>> -    cdw = container_of(work, struct acpi_scan_clear_dep_work, work);
>>>> +    struct acpi_device *adev = to_acpi_device(dev);
>>>>
>>>>      acpi_scan_lock_acquire();
>>>> -    acpi_bus_attach(cdw->adev, (void *)true);
>>>> +    acpi_bus_attach(adev, (void *)true);
>>>>      acpi_scan_lock_release();
>>>>
>>>> -    acpi_dev_put(cdw->adev);
>>>> -    kfree(cdw);
>>>> +    acpi_dev_put(adev);
>>>>  }
>>>>
>>>>  static bool acpi_scan_clear_dep_queue(struct acpi_device *adev)
>>>>  {
>>>> -    struct acpi_scan_clear_dep_work *cdw;
>>>> -
>>>>      if (adev->dep_unmet)
>>>>              return false;
>>>>
>>>> -    cdw = kmalloc(sizeof(*cdw), GFP_KERNEL);
>>>> -    if (!cdw)
>>>> -            return false;
>>>> -
>>>> -    cdw->adev = adev;
>>>> -    INIT_WORK(&cdw->work, acpi_scan_clear_dep_fn);
>>>>      /*
>>>> -     * Since the work function may block on the lock until the entire
>>>> -     * initial enumeration of devices is complete, put it into the unbound
>>>> -     * workqueue.
>>>> +     * Async schedule the deferred acpi_scan_clear_dep_fn() since:
>>>> +     * - acpi_bus_attach() needs to hold acpi_scan_lock which cannot
>>>> +     *   be acquired under acpi_dep_list_lock (held here)
>>>> +     * - the deferred work at boot stage is ensured to be finished
>>>> +     *   before entering init task by the async_synchronize_full()
>>>> +     *   barrier
>>>> +     *
>>>> +     * Use _nocall variant since it'll return on failure instead of
>>>> +     * run the function synchronously.
>>>>       */
>>>> -    queue_work(system_dfl_wq, &cdw->work);
>>>> +    if (!async_schedule_dev_nocall(acpi_scan_clear_dep_fn, &adev->dev))
>>>> +            return false;
>>>
>>> This really feels wrong to me, you are taking a code path that has been
>>> working for quite a while and changing it.  Perhaps your system ACPI
>>> tables are the thing that is incorrect here?
>>>
>>> What exactly is the problem that you are seeing?  Why not start with
>>> that and then we can work out how to solve that issue?
>>>
>>
>> two issues here we met (as briefly mentioned in the commit and cover letter):
>> 1. kernel panic due to userspace init cannot have an opened console. the
>>    console device scanning is queued in the system_dfl_wq in above code
>>    and not finished by the time userspace init process running, thus by
>>    the time userspace init running, no console is created
>> 2. entering rescue shell due to no root devices (PCIe nvme in our case)
>>    found. same reason as above, the PCIe host bridge scanning is queued
>>    in above and finished after init process running.
>>
>> The reason why these devices are created here is because they both depend
>> on riscv-aplic irqchip to serve their interrupts (console's wired
>> interrupt and PCI's INTx interrupts) and in order to keep the dependency
>> these devices are scanned and created after riscv-aplic initialized. The
>> riscv-aplic is initialized in device_initcall and invoke above codes for
>> the scan/creation of these devices, it's close to the time running
>> userspace init process. Since system_dfl_wq is used here and no synchronized
>> mechanism, the issues will happen if userspace init runs before these devices
>> are ready.
> 
> Well, there is flush_workqueue(), isn't it there?
> 

sure, of course. I implement it using async schedule but open to any
better ones. but..

>> Previous solution [1] is to advance the initialization of riscv-aplic
>> earlier but the order still cannot be guaranteed conceptually.
>> With async_schedule_dev_nocal() the work queued is finished
>> before entering userspace init since we'll wait for completion at
>> async_synchronize_full() before executing userspace init process.
>>
>> To solve the issue I think we should make these devices ready before
>> entering userspace and async schedule is one way to make it. It's also
>> using an unbound workqueue but have additional synchronization. Any
>> corrections or suggestions?
> 
> You can flush the dedicated workqueue at the same spot where you do
> async_synchronize_full(), can't you?
> 

the async_synchronize_full() is already there in the init code right
before entering usersapce [1] so if we use async schedule we don't
need to add synchronize spot ourselves. For a dedicated workqueue we
need to call flush_workqueue() explicitly somewhere (I suppose to be
the last level initcall like late_initcall_sync). Furthermore we need
to allocate it and I think not all the platforms need this piece of
code.

It seems no need to have a dedicated workqueue for this since async
schedule can satisfy the needs already (from my view). Except less
modifications can be made for this piece of code if we use a dedicated
workqueue, is this the consideration and mandatory?

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/init/main.c?h=v6.19-rc6#n1580

thanks.

On Thu, Jan 22, 2026 at 2:48 PM Yicong Yang <yang.yicong@picoheart.com> wrote:
>
> On 1/22/26 9:21 PM, Rafael J. Wysocki wrote:
> > On Thu, Jan 22, 2026 at 1:43 PM Yicong Yang <yang.yicong@picoheart.com> wrote:
> >>
> >> On 1/22/26 6:29 PM, Greg KH wrote:
> >>> On Thu, Jan 22, 2026 at 03:34:45PM +0800, Yicong Yang wrote:
> >>>> The device object rescan in acpi_scan_clear_dep_fn is scheduled
> >>>> in the system workqueue which is not guaranteed to be finished
> >>>> before entering userspace. This will cause the problem that
> >>>> some key devices are missed when the init task try to find them,
> >>>> e.g. console devices and root devices (PCIe nvme, etc).
> >>>> This issues is more possbile to happen on RISCV since these
> >>>> devices using GSI interrupt may depend on APLIC and will be
> >>>> scanned in acpi_scan_clear_dep_queue() after APLIC initialized.
> >>>>
> >>>> Fix this by scheduling the acpi_scan_clear_dep_queue() using async
> >>>> schedule function rather than the system workqueue. The deferred
> >>>> works will be synchronized by async_synchronize_full() before
> >>>> entering init task.
> >>>>
> >>>> Update the comment as well.
> >>>>
> >>>> Signed-off-by: Yicong Yang <yang.yicong@picoheart.com>
> >>>> ---
> >>>>  drivers/acpi/scan.c | 35 ++++++++++++++++-------------------
> >>>>  1 file changed, 16 insertions(+), 19 deletions(-)
> >>>>
> >>>> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> >>>> index 416d87f9bd10..bf0d8ba9ba19 100644
> >>>> --- a/drivers/acpi/scan.c
> >>>> +++ b/drivers/acpi/scan.c
> >>>> @@ -5,6 +5,7 @@
> >>>>
> >>>>  #define pr_fmt(fmt) "ACPI: " fmt
> >>>>
> >>>> +#include <linux/async.h>
> >>>>  #include <linux/module.h>
> >>>>  #include <linux/init.h>
> >>>>  #include <linux/slab.h>
> >>>> @@ -2365,39 +2366,35 @@ struct acpi_scan_clear_dep_work {
> >>>>      struct acpi_device *adev;
> >>>>  };
> >>>>
> >>>> -static void acpi_scan_clear_dep_fn(struct work_struct *work)
> >>>> +static void acpi_scan_clear_dep_fn(void *dev, async_cookie_t cookie)
> >>>>  {
> >>>> -    struct acpi_scan_clear_dep_work *cdw;
> >>>> -
> >>>> -    cdw = container_of(work, struct acpi_scan_clear_dep_work, work);
> >>>> +    struct acpi_device *adev = to_acpi_device(dev);
> >>>>
> >>>>      acpi_scan_lock_acquire();
> >>>> -    acpi_bus_attach(cdw->adev, (void *)true);
> >>>> +    acpi_bus_attach(adev, (void *)true);
> >>>>      acpi_scan_lock_release();
> >>>>
> >>>> -    acpi_dev_put(cdw->adev);
> >>>> -    kfree(cdw);
> >>>> +    acpi_dev_put(adev);
> >>>>  }
> >>>>
> >>>>  static bool acpi_scan_clear_dep_queue(struct acpi_device *adev)
> >>>>  {
> >>>> -    struct acpi_scan_clear_dep_work *cdw;
> >>>> -
> >>>>      if (adev->dep_unmet)
> >>>>              return false;
> >>>>
> >>>> -    cdw = kmalloc(sizeof(*cdw), GFP_KERNEL);
> >>>> -    if (!cdw)
> >>>> -            return false;
> >>>> -
> >>>> -    cdw->adev = adev;
> >>>> -    INIT_WORK(&cdw->work, acpi_scan_clear_dep_fn);
> >>>>      /*
> >>>> -     * Since the work function may block on the lock until the entire
> >>>> -     * initial enumeration of devices is complete, put it into the unbound
> >>>> -     * workqueue.
> >>>> +     * Async schedule the deferred acpi_scan_clear_dep_fn() since:
> >>>> +     * - acpi_bus_attach() needs to hold acpi_scan_lock which cannot
> >>>> +     *   be acquired under acpi_dep_list_lock (held here)
> >>>> +     * - the deferred work at boot stage is ensured to be finished
> >>>> +     *   before entering init task by the async_synchronize_full()
> >>>> +     *   barrier
> >>>> +     *
> >>>> +     * Use _nocall variant since it'll return on failure instead of
> >>>> +     * run the function synchronously.
> >>>>       */
> >>>> -    queue_work(system_dfl_wq, &cdw->work);
> >>>> +    if (!async_schedule_dev_nocall(acpi_scan_clear_dep_fn, &adev->dev))
> >>>> +            return false;
> >>>
> >>> This really feels wrong to me, you are taking a code path that has been
> >>> working for quite a while and changing it.  Perhaps your system ACPI
> >>> tables are the thing that is incorrect here?
> >>>
> >>> What exactly is the problem that you are seeing?  Why not start with
> >>> that and then we can work out how to solve that issue?
> >>>
> >>
> >> two issues here we met (as briefly mentioned in the commit and cover letter):
> >> 1. kernel panic due to userspace init cannot have an opened console. the
> >>    console device scanning is queued in the system_dfl_wq in above code
> >>    and not finished by the time userspace init process running, thus by
> >>    the time userspace init running, no console is created
> >> 2. entering rescue shell due to no root devices (PCIe nvme in our case)
> >>    found. same reason as above, the PCIe host bridge scanning is queued
> >>    in above and finished after init process running.
> >>
> >> The reason why these devices are created here is because they both depend
> >> on riscv-aplic irqchip to serve their interrupts (console's wired
> >> interrupt and PCI's INTx interrupts) and in order to keep the dependency
> >> these devices are scanned and created after riscv-aplic initialized. The
> >> riscv-aplic is initialized in device_initcall and invoke above codes for
> >> the scan/creation of these devices, it's close to the time running
> >> userspace init process. Since system_dfl_wq is used here and no synchronized
> >> mechanism, the issues will happen if userspace init runs before these devices
> >> are ready.
> >
> > Well, there is flush_workqueue(), isn't it there?
> >
>
> sure, of course. I implement it using async schedule but open to any
> better ones. but..
>
> >> Previous solution [1] is to advance the initialization of riscv-aplic
> >> earlier but the order still cannot be guaranteed conceptually.
> >> With async_schedule_dev_nocal() the work queued is finished
> >> before entering userspace init since we'll wait for completion at
> >> async_synchronize_full() before executing userspace init process.
> >>
> >> To solve the issue I think we should make these devices ready before
> >> entering userspace and async schedule is one way to make it. It's also
> >> using an unbound workqueue but have additional synchronization. Any
> >> corrections or suggestions?
> >
> > You can flush the dedicated workqueue at the same spot where you do
> > async_synchronize_full(), can't you?
> >
>
> the async_synchronize_full() is already there in the init code right
> before entering usersapce [1] so if we use async schedule we don't
> need to add synchronize spot ourselves. For a dedicated workqueue we
> need to call flush_workqueue() explicitly somewhere (I suppose to be
> the last level initcall like late_initcall_sync). Furthermore we need
> to allocate it and I think not all the platforms need this piece of
> code.
>
> It seems no need to have a dedicated workqueue for this since async
> schedule can satisfy the needs already (from my view). Except less
> modifications can be made for this piece of code if we use a dedicated
> workqueue, is this the consideration and mandatory?
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/init/main.c?h=v6.19-rc6#n1580

So please add the above information to the changelog of your patch
(that is, why it is better to use async for this than to use a
dedicated workqueue in your view) because it is kind of relevant.

And how does the second patch in the series depend on this one?

On 1/22/26 9:57 PM, Rafael J. Wysocki wrote:
> On Thu, Jan 22, 2026 at 2:48 PM Yicong Yang <yang.yicong@picoheart.com> wrote:
>>
>> On 1/22/26 9:21 PM, Rafael J. Wysocki wrote:
>>> On Thu, Jan 22, 2026 at 1:43 PM Yicong Yang <yang.yicong@picoheart.com> wrote:
>>>>
>>>> On 1/22/26 6:29 PM, Greg KH wrote:
>>>>> On Thu, Jan 22, 2026 at 03:34:45PM +0800, Yicong Yang wrote:
>>>>>> The device object rescan in acpi_scan_clear_dep_fn is scheduled
>>>>>> in the system workqueue which is not guaranteed to be finished
>>>>>> before entering userspace. This will cause the problem that
>>>>>> some key devices are missed when the init task try to find them,
>>>>>> e.g. console devices and root devices (PCIe nvme, etc).
>>>>>> This issues is more possbile to happen on RISCV since these
>>>>>> devices using GSI interrupt may depend on APLIC and will be
>>>>>> scanned in acpi_scan_clear_dep_queue() after APLIC initialized.
>>>>>>
>>>>>> Fix this by scheduling the acpi_scan_clear_dep_queue() using async
>>>>>> schedule function rather than the system workqueue. The deferred
>>>>>> works will be synchronized by async_synchronize_full() before
>>>>>> entering init task.
>>>>>>
>>>>>> Update the comment as well.
>>>>>>
>>>>>> Signed-off-by: Yicong Yang <yang.yicong@picoheart.com>
>>>>>> ---
>>>>>>  drivers/acpi/scan.c | 35 ++++++++++++++++-------------------
>>>>>>  1 file changed, 16 insertions(+), 19 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
>>>>>> index 416d87f9bd10..bf0d8ba9ba19 100644
>>>>>> --- a/drivers/acpi/scan.c
>>>>>> +++ b/drivers/acpi/scan.c
>>>>>> @@ -5,6 +5,7 @@
>>>>>>
>>>>>>  #define pr_fmt(fmt) "ACPI: " fmt
>>>>>>
>>>>>> +#include <linux/async.h>
>>>>>>  #include <linux/module.h>
>>>>>>  #include <linux/init.h>
>>>>>>  #include <linux/slab.h>
>>>>>> @@ -2365,39 +2366,35 @@ struct acpi_scan_clear_dep_work {
>>>>>>      struct acpi_device *adev;
>>>>>>  };
>>>>>>
>>>>>> -static void acpi_scan_clear_dep_fn(struct work_struct *work)
>>>>>> +static void acpi_scan_clear_dep_fn(void *dev, async_cookie_t cookie)
>>>>>>  {
>>>>>> -    struct acpi_scan_clear_dep_work *cdw;
>>>>>> -
>>>>>> -    cdw = container_of(work, struct acpi_scan_clear_dep_work, work);
>>>>>> +    struct acpi_device *adev = to_acpi_device(dev);
>>>>>>
>>>>>>      acpi_scan_lock_acquire();
>>>>>> -    acpi_bus_attach(cdw->adev, (void *)true);
>>>>>> +    acpi_bus_attach(adev, (void *)true);
>>>>>>      acpi_scan_lock_release();
>>>>>>
>>>>>> -    acpi_dev_put(cdw->adev);
>>>>>> -    kfree(cdw);
>>>>>> +    acpi_dev_put(adev);
>>>>>>  }
>>>>>>
>>>>>>  static bool acpi_scan_clear_dep_queue(struct acpi_device *adev)
>>>>>>  {
>>>>>> -    struct acpi_scan_clear_dep_work *cdw;
>>>>>> -
>>>>>>      if (adev->dep_unmet)
>>>>>>              return false;
>>>>>>
>>>>>> -    cdw = kmalloc(sizeof(*cdw), GFP_KERNEL);
>>>>>> -    if (!cdw)
>>>>>> -            return false;
>>>>>> -
>>>>>> -    cdw->adev = adev;
>>>>>> -    INIT_WORK(&cdw->work, acpi_scan_clear_dep_fn);
>>>>>>      /*
>>>>>> -     * Since the work function may block on the lock until the entire
>>>>>> -     * initial enumeration of devices is complete, put it into the unbound
>>>>>> -     * workqueue.
>>>>>> +     * Async schedule the deferred acpi_scan_clear_dep_fn() since:
>>>>>> +     * - acpi_bus_attach() needs to hold acpi_scan_lock which cannot
>>>>>> +     *   be acquired under acpi_dep_list_lock (held here)
>>>>>> +     * - the deferred work at boot stage is ensured to be finished
>>>>>> +     *   before entering init task by the async_synchronize_full()
>>>>>> +     *   barrier
>>>>>> +     *
>>>>>> +     * Use _nocall variant since it'll return on failure instead of
>>>>>> +     * run the function synchronously.
>>>>>>       */
>>>>>> -    queue_work(system_dfl_wq, &cdw->work);
>>>>>> +    if (!async_schedule_dev_nocall(acpi_scan_clear_dep_fn, &adev->dev))
>>>>>> +            return false;
>>>>>
>>>>> This really feels wrong to me, you are taking a code path that has been
>>>>> working for quite a while and changing it.  Perhaps your system ACPI
>>>>> tables are the thing that is incorrect here?
>>>>>
>>>>> What exactly is the problem that you are seeing?  Why not start with
>>>>> that and then we can work out how to solve that issue?
>>>>>
>>>>
>>>> two issues here we met (as briefly mentioned in the commit and cover letter):
>>>> 1. kernel panic due to userspace init cannot have an opened console. the
>>>>    console device scanning is queued in the system_dfl_wq in above code
>>>>    and not finished by the time userspace init process running, thus by
>>>>    the time userspace init running, no console is created
>>>> 2. entering rescue shell due to no root devices (PCIe nvme in our case)
>>>>    found. same reason as above, the PCIe host bridge scanning is queued
>>>>    in above and finished after init process running.
>>>>
>>>> The reason why these devices are created here is because they both depend
>>>> on riscv-aplic irqchip to serve their interrupts (console's wired
>>>> interrupt and PCI's INTx interrupts) and in order to keep the dependency
>>>> these devices are scanned and created after riscv-aplic initialized. The
>>>> riscv-aplic is initialized in device_initcall and invoke above codes for
>>>> the scan/creation of these devices, it's close to the time running
>>>> userspace init process. Since system_dfl_wq is used here and no synchronized
>>>> mechanism, the issues will happen if userspace init runs before these devices
>>>> are ready.
>>>
>>> Well, there is flush_workqueue(), isn't it there?
>>>
>>
>> sure, of course. I implement it using async schedule but open to any
>> better ones. but..
>>
>>>> Previous solution [1] is to advance the initialization of riscv-aplic
>>>> earlier but the order still cannot be guaranteed conceptually.
>>>> With async_schedule_dev_nocal() the work queued is finished
>>>> before entering userspace init since we'll wait for completion at
>>>> async_synchronize_full() before executing userspace init process.
>>>>
>>>> To solve the issue I think we should make these devices ready before
>>>> entering userspace and async schedule is one way to make it. It's also
>>>> using an unbound workqueue but have additional synchronization. Any
>>>> corrections or suggestions?
>>>
>>> You can flush the dedicated workqueue at the same spot where you do
>>> async_synchronize_full(), can't you?
>>>
>>
>> the async_synchronize_full() is already there in the init code right
>> before entering usersapce [1] so if we use async schedule we don't
>> need to add synchronize spot ourselves. For a dedicated workqueue we
>> need to call flush_workqueue() explicitly somewhere (I suppose to be
>> the last level initcall like late_initcall_sync). Furthermore we need
>> to allocate it and I think not all the platforms need this piece of
>> code.
>>
>> It seems no need to have a dedicated workqueue for this since async
>> schedule can satisfy the needs already (from my view). Except less
>> modifications can be made for this piece of code if we use a dedicated
>> workqueue, is this the consideration and mandatory?
>>
>> [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/init/main.c?h=v6.19-rc6#n1580
> 
> So please add the above information to the changelog of your patch
> (that is, why it is better to use async for this than to use a
> dedicated workqueue in your view) because it is kind of relevant.

sure. will add these in the commit in next version.

> 
> And how does the second patch in the series depend on this one?

these two are independent patches but to fix the same class of issue.
this one is for the real issue we met and the second one is a theoretical
possible issue found during discussion on my previous solution. I may
send them separately since the second one maybe not a problem in real case,
will wait for more feedback.

thanks.