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[RFC,v2,07/35] x86: intel_epb: Don't rely on link order

Message ID 20230913163823.7880-8-james.morse@arm.com (mailing list archive)
State RFC, archived
Headers show
Series ACPI/arm64: add support for virtual cpuhotplug | expand

Commit Message

James Morse Sept. 13, 2023, 4:37 p.m. UTC
intel_epb_init() is called as a subsys_initcall() to register cpuhp
callbacks. The callbacks make use of get_cpu_device() which will return
NULL unless register_cpu() has been called. register_cpu() is called
from topology_init(), which is also a subsys_initcall().

This is fragile. Moving the register_cpu() to a different
subsys_initcall()  leads to a NULL derefernce during boot.

Make intel_epb_init() a late_initcall(), user-space can't provide a
policy before this point anyway.

Signed-off-by: James Morse <james.morse@arm.com>
---
subsys_initcall_sync() would be an option, but moving the register_cpu()
calls into ACPI also means adding a safety net for CPUs that are online
but not described properly by firmware. This lives in subsys_initcall_sync().
---
 arch/x86/kernel/cpu/intel_epb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Russell King (Oracle) Sept. 14, 2023, 10:02 a.m. UTC | #1
On Wed, Sep 13, 2023 at 04:37:55PM +0000, James Morse wrote:
> intel_epb_init() is called as a subsys_initcall() to register cpuhp
> callbacks. The callbacks make use of get_cpu_device() which will return
> NULL unless register_cpu() has been called. register_cpu() is called
> from topology_init(), which is also a subsys_initcall().
> 
> This is fragile. Moving the register_cpu() to a different
> subsys_initcall()  leads to a NULL derefernce during boot.
> 
> Make intel_epb_init() a late_initcall(), user-space can't provide a
> policy before this point anyway.
> 
> Signed-off-by: James Morse <james.morse@arm.com>

I think someone knowledgeable from x86 land needs to ack/review this.
Gavin Shan Sept. 18, 2023, 3:48 a.m. UTC | #2
On 9/14/23 02:37, James Morse wrote:
> intel_epb_init() is called as a subsys_initcall() to register cpuhp
> callbacks. The callbacks make use of get_cpu_device() which will return
> NULL unless register_cpu() has been called. register_cpu() is called
> from topology_init(), which is also a subsys_initcall().
> 
> This is fragile. Moving the register_cpu() to a different
> subsys_initcall()  leads to a NULL derefernce during boot.
                                      ^^^^^^^^^^
                                      s/derefernce/dereference

Reported by ./scripts/checkpatch.pl --codespell

> 
> Make intel_epb_init() a late_initcall(), user-space can't provide a
> policy before this point anyway.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> subsys_initcall_sync() would be an option, but moving the register_cpu()
> calls into ACPI also means adding a safety net for CPUs that are online
> but not described properly by firmware. This lives in subsys_initcall_sync().
> ---
>   arch/x86/kernel/cpu/intel_epb.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/cpu/intel_epb.c b/arch/x86/kernel/cpu/intel_epb.c
> index e4c3ba91321c..f18d35fe27a9 100644
> --- a/arch/x86/kernel/cpu/intel_epb.c
> +++ b/arch/x86/kernel/cpu/intel_epb.c
> @@ -237,4 +237,4 @@ static __init int intel_epb_init(void)
>   	cpuhp_remove_state(CPUHP_AP_X86_INTEL_EPB_ONLINE);
>   	return ret;
>   }
> -subsys_initcall(intel_epb_init);
> +late_initcall(intel_epb_init);

Thanks,
Gavin
diff mbox series

Patch

diff --git a/arch/x86/kernel/cpu/intel_epb.c b/arch/x86/kernel/cpu/intel_epb.c
index e4c3ba91321c..f18d35fe27a9 100644
--- a/arch/x86/kernel/cpu/intel_epb.c
+++ b/arch/x86/kernel/cpu/intel_epb.c
@@ -237,4 +237,4 @@  static __init int intel_epb_init(void)
 	cpuhp_remove_state(CPUHP_AP_X86_INTEL_EPB_ONLINE);
 	return ret;
 }
-subsys_initcall(intel_epb_init);
+late_initcall(intel_epb_init);