Re: [PATCH] riscv: Move call to init_cpu_topology() to later initialization stage

From: Conor Dooley <conor@kernel.org>
To: Ley Foon Tan <leyfoon.tan@starfivetech.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	Ley Foon Tan <lftan.linux@gmail.com>
Subject: Re: [PATCH] riscv: Move call to init_cpu_topology() to later initialization stage
Date: Wed, 4 Jan 2023 13:00:31 +0000	[thread overview]
Message-ID: <Y7V4byskevAWKM3G@spud> (raw)
In-Reply-To: <20230103035316.3841303-1-leyfoon.tan@starfivetech.com>

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Hey Ley Foon Tan,

Apologies for my various bits of confusion.

On Tue, Jan 03, 2023 at 11:53:16AM +0800, Ley Foon Tan wrote:
> topology_parse_cpu_capacity() is failed to allocate memory with kcalloc()
> after read "capacity-dmips-mhz" DT parameter in CPU DT nodes. This
> topology_parse_cpu_capacity() is called from init_cpu_topology(), move
> call to init_cpu_topology() to later initialization  stage (after memory
> allocation is available).
> 
> Note, this refers to ARM64 implementation, call init_cpu_topology() in
> smp_prepare_cpus().
> 
> Tested on Qemu platform.

I'd like to suggest a change to the commit message:
```
If "capacity-dmips-mhz" is present in a CPU DT node,
topology_parse_cpu_capacity() will fail to allocate memory.
arm64, with which this code path is shared, does not call
topology_parse_cpu_capacity() until later in boot where memory
allocation is available.
While "capacity-dmips-mhz" is not yet a valid property on RISC-V,
invalid properties should be ignored rather than cause issues.
Move init_cpu_topology(), which calls topology_parse_cpu_capacity(),
to a later initialization stage, to match arm64.

As a side effect of this change, RISC-V is "protected" from changes to
core topology code that would work on arm64 where memory allocation is
safe but on RISC-V isn't.
```

You don't need to use exactly that, but with something along those
lines:
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>

Thanks,
Conor.

> 
> Signed-off-by: Ley Foon Tan <leyfoon.tan@starfivetech.com>
> 
> ---
> 
> In drivers/base/arch_topology.c: topology_parse_cpu_capacity():
> 
> 	ret = of_property_read_u32(cpu_node, "capacity-dmips-mhz",
> 				   &cpu_capacity);
> 	if (!ret) {
> 		if (!raw_capacity) {
> 			raw_capacity = kcalloc(num_possible_cpus(),
> 					       sizeof(*raw_capacity),
> 					       GFP_KERNEL);
> 			if (!raw_capacity) {
> 				cap_parsing_failed = true;
> 				return false;
> 			}
> ---
>  arch/riscv/kernel/smpboot.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> index 3373df413c88..ddb2afba6d25 100644
> --- a/arch/riscv/kernel/smpboot.c
> +++ b/arch/riscv/kernel/smpboot.c
> @@ -39,7 +39,6 @@ static DECLARE_COMPLETION(cpu_running);
>  
>  void __init smp_prepare_boot_cpu(void)
>  {
> -	init_cpu_topology();
>  }
>  
>  void __init smp_prepare_cpus(unsigned int max_cpus)
> @@ -48,6 +47,8 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
>  	int ret;
>  	unsigned int curr_cpuid;
>  
> +	init_cpu_topology();
> +
>  	curr_cpuid = smp_processor_id();
>  	store_cpu_topology(curr_cpuid);
>  	numa_store_cpu_info(curr_cpuid);
> -- 
> 2.25.1
> 

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