Since 97f8172f9a98 ("init/initramfs.c: do unpacking asynchronously") I get
the following warning early in the boot process from umh:
"wait_for_initramfs() called before rootfs_initcalls"
Some debugging lead me to the following call chain:
kernel_init_freeable()
-> do_basic_setup()
-> driver_init()
-> platform_bus_init()
-> bus_register()
-> kset_register()
-> kobject_uvent()
On 29.04.2021 08:46, Heiner Kallweit wrote:
> Since 97f8172f9a98 ("init/initramfs.c: do unpacking asynchronously") I get
> the following warning early in the boot process from umh:
> "wait_for_initramfs() called before rootfs_initcalls"
> Some debugging lead me to the following call chain:
>
> kernel_init_freeable()
> -> do_basic_setup()
> -> driver_init()
> -> platform_bus_init()
> -> bus_register()
> -> kset_register()
> -> kobject_uvent()
>
Sorry, this is the first umh call, but at this time UMH_DISABLED is still set.
The first umh call where UMH is enabled is the following:
kernel_init_freeable()
-> do_basic_setup()
-> do_initcalls()
-> do_one_initcall()
-> wq_sysfs_init() <- core_initcall()
-> subsys_virtual_register()
-> bus_register()
On 29/04/2021 09.16, Heiner Kallweit wrote:
> On 29.04.2021 08:46, Heiner Kallweit wrote:
>> Since 97f8172f9a98 ("init/initramfs.c: do unpacking asynchronously") I get
>> the following warning early in the boot process from umh:
>> "wait_for_initramfs() called before rootfs_initcalls"
>> Some debugging lead me to the following call chain:
>>
>> kernel_init_freeable()
>> -> do_basic_setup()
>> -> driver_init()
>> -> platform_bus_init()
>> -> bus_register()
>> -> kset_register()
>> -> kobject_uvent()
>>
>
> Sorry, this is the first umh call, but at this time UMH_DISABLED is still set.
> The first umh call where UMH is enabled is the following:
>
> kernel_init_freeable()
> -> do_basic_setup()
> -> do_initcalls()
> -> do_one_initcall()
> -> wq_sysfs_init() <- core_initcall()
> -> subsys_virtual_register()
> -> bus_register()
>
Thanks for the report. Do you have CONFIG_UEVENT_HELPER=y and
CONFIG_UEVENT_HELPER_PATH set to a non-empty string? Assuming yes:
I did notice that on backporting those patches to an old BSP of ours,
but the other platforms I had done those patches for didn't have
UEVENT_HELPER set, so didn't know about until about a week ago.
Emitting calls to /sbin/hotplug before the initramfs has had a chance to
begin being unpacked is a complete waste of cycles (it's a _lot_ of
kernel threads being forked only to fail with -ENOENT because there's no
such binary, or any other fs contents for that matter). Just keeping
CONFIG_UEVENT_HELPER set but clearing CONFIG_UEVENT_HELPER_PATH (if
actually needed, userspace can set it appropriately later) made booting
quite noticably faster on that old and slow cpu.
So in a sense, that warning has served its purpose: drawing attention to
a deficiency in the boot process (at least with such a .config).
A few options:
(1) Do nothing, have people reconsider whether they really need
UEVENT_HELPER_PATH set.
(2) Move the usermodehelper_enable() call from do_basic_setup() to
around rootfs_initcall time. Perhaps in populate_rootfs() itself, right
after scheduling do_populate_rootfs(). And a similar call would need to
be added in default_rootfs() in noinitramfs.c for the
CONFIG_BLK_DEV_INITRD=n case. Or a separate rootfs_initcall() in
kernel/umh.c itself, if we can rely on link order to put that after
populate_rootfs.
I think (2) would eliminate the warning, but then the very first uevent
from some random device probe will cause that wait_for_initramfs(), i.e.
it will effectively end up making the initramfs unpacking synchronous
for anybody with CONFIG_UEVENT_HELPER_PATH!="". I can live with that, of
course, but OTOH it's a bit sad that they'd never have a way to know
that they could boot faster by eliminating a legacy setting from their
.config.
Rasmus
On 29.04.2021 10:18, Rasmus Villemoes wrote:
> On 29/04/2021 09.16, Heiner Kallweit wrote:
>> On 29.04.2021 08:46, Heiner Kallweit wrote:
>>> Since 97f8172f9a98 ("init/initramfs.c: do unpacking asynchronously") I get
>>> the following warning early in the boot process from umh:
>>> "wait_for_initramfs() called before rootfs_initcalls"
>>> Some debugging lead me to the following call chain:
>>>
>>> kernel_init_freeable()
>>> -> do_basic_setup()
>>> -> driver_init()
>>> -> platform_bus_init()
>>> -> bus_register()
>>> -> kset_register()
>>> -> kobject_uvent()
>>>
>>
>> Sorry, this is the first umh call, but at this time UMH_DISABLED is still set.
>> The first umh call where UMH is enabled is the following:
>>
>> kernel_init_freeable()
>> -> do_basic_setup()
>> -> do_initcalls()
>> -> do_one_initcall()
>> -> wq_sysfs_init() <- core_initcall()
>> -> subsys_virtual_register()
>> -> bus_register()
>>
>
> Thanks for the report. Do you have CONFIG_UEVENT_HELPER=y and
> CONFIG_UEVENT_HELPER_PATH set to a non-empty string? Assuming yes:
>
Thanks for the prompt response. Yes, that's the config here:
CONFIG_UEVENT_HELPER=y
CONFIG_UEVENT_HELPER_PATH="/sbin/hotplug"
I now disabled CONFIG_UEVENT_HELPER and don't have the warning
any longer. Maybe, what could be done so that you don't have to
explain the same thing a hundred times to people like me:
In case the warning is harmless, make it info or notice and add
a hint like this to the message "please reconsider whether you
really need config option CONFIG_UEVENT_HELPER".
> I did notice that on backporting those patches to an old BSP of ours,
> but the other platforms I had done those patches for didn't have
> UEVENT_HELPER set, so didn't know about until about a week ago.
>
> Emitting calls to /sbin/hotplug before the initramfs has had a chance to
> begin being unpacked is a complete waste of cycles (it's a _lot_ of
> kernel threads being forked only to fail with -ENOENT because there's no
> such binary, or any other fs contents for that matter). Just keeping
> CONFIG_UEVENT_HELPER set but clearing CONFIG_UEVENT_HELPER_PATH (if
> actually needed, userspace can set it appropriately later) made booting
> quite noticably faster on that old and slow cpu.
>
> So in a sense, that warning has served its purpose: drawing attention to
> a deficiency in the boot process (at least with such a .config).
>
> A few options:
>
> (1) Do nothing, have people reconsider whether they really need
> UEVENT_HELPER_PATH set.
>
> (2) Move the usermodehelper_enable() call from do_basic_setup() to
> around rootfs_initcall time. Perhaps in populate_rootfs() itself, right
> after scheduling do_populate_rootfs(). And a similar call would need to
> be added in default_rootfs() in noinitramfs.c for the
> CONFIG_BLK_DEV_INITRD=n case. Or a separate rootfs_initcall() in
> kernel/umh.c itself, if we can rely on link order to put that after
> populate_rootfs.
>
> I think (2) would eliminate the warning, but then the very first uevent
> from some random device probe will cause that wait_for_initramfs(), i.e.
> it will effectively end up making the initramfs unpacking synchronous
> for anybody with CONFIG_UEVENT_HELPER_PATH!="". I can live with that, of
> course, but OTOH it's a bit sad that they'd never have a way to know
> that they could boot faster by eliminating a legacy setting from their
> .config.
>
> Rasmus
>
Heiner