diff mbox series

[RFC,02/22] x86: intel_epb: Don't rely on link order

Message ID E1r0JKq-00CTwZ-Mh@rmk-PC.armlinux.org.uk
State New
Headers show
Series Initial cleanups for vCPU hotplug | expand

Commit Message

Russell King (Oracle) Nov. 7, 2023, 10:29 a.m. UTC
From: James Morse <james.morse@arm.com>

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 dereference 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>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
---
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

Gavin Shan Nov. 13, 2023, 12:03 a.m. UTC | #1
On 11/7/23 20:29, Russell King (Oracle) wrote:
> From: James Morse <james.morse@arm.com>
> 
> 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 dereference 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>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> ---
> 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(-)
> 

Reviewed-by: Gavin Shan <gshan@redhat.com>
Jonathan Cameron Nov. 28, 2023, 2:40 p.m. UTC | #2
On Tue, 07 Nov 2023 10:29:28 +0000
Russell King <rmk+kernel@armlinux.org.uk> wrote:

> From: James Morse <james.morse@arm.com>
> 
> 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 dereference 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>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

Seems reasonable. FWIW
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.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);
Russell King (Oracle) Nov. 28, 2023, 3:42 p.m. UTC | #3
On Tue, Nov 28, 2023 at 02:40:59PM +0000, Jonathan Cameron wrote:
> On Tue, 07 Nov 2023 10:29:28 +0000
> Russell King <rmk+kernel@armlinux.org.uk> wrote:
> 
> > From: James Morse <james.morse@arm.com>
> > 
> > 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 dereference 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>
> > Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> 
> Seems reasonable. FWIW
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Thanks, however this has already been merged into the tip tree since
Rafael suggested sending it separately.
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);