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Date: Thu, 18 Jan 2024 20:42:25 -0800
From: Yury Norov <yury.norov@...il.com>
To: Huang Shijie <shijie@...amperecomputing.com>
Cc: gregkh@...uxfoundation.org, patches@...erecomputing.com,
rafael@...nel.org, paul.walmsley@...ive.com, palmer@...belt.com,
aou@...s.berkeley.edu, kuba@...nel.org, vschneid@...hat.com,
mingo@...nel.org, akpm@...ux-foundation.org, vbabka@...e.cz,
rppt@...nel.org, tglx@...utronix.de, jpoimboe@...nel.org,
ndesaulniers@...gle.com, mikelley@...rosoft.com,
mhiramat@...nel.org, arnd@...db.de, linux-kernel@...r.kernel.org,
linux-riscv@...ts.infradead.org,
linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com,
will@...nel.org, mark.rutland@....com, mpe@...erman.id.au,
linuxppc-dev@...ts.ozlabs.org, chenhuacai@...nel.org,
jiaxun.yang@...goat.com, linux-mips@...r.kernel.org,
cl@...amperecomputing.com
Subject: Re: [PATCH] NUMA: Early use of cpu_to_node() returns 0 instead of
the correct node id
On Fri, Jan 19, 2024 at 11:32:27AM +0800, Huang Shijie wrote:
> hZ7bkEvc+Z19RHkS/HVG3KMg
> X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM8PR01MB7144
> Status: O
> Content-Length: 3779
> Lines: 126
>
> During the kernel booting, the generic cpu_to_node() is called too early in
> arm64, powerpc and riscv when CONFIG_NUMA is enabled.
>
> There are at least four places in the common code where
> the generic cpu_to_node() is called before it is initialized:
> 1.) early_trace_init() in kernel/trace/trace.c
> 2.) sched_init() in kernel/sched/core.c
> 3.) init_sched_fair_class() in kernel/sched/fair.c
> 4.) workqueue_init_early() in kernel/workqueue.c
>
> In order to fix the bug, the patch changes generic cpu_to_node to
> function pointer, and export it for kernel modules.
> Introduce smp_prepare_boot_cpu_start() to wrap the original
> smp_prepare_boot_cpu(), and set cpu_to_node with early_cpu_to_node.
> Introduce smp_prepare_cpus_done() to wrap the original smp_prepare_cpus(),
> and set the cpu_to_node to formal _cpu_to_node().
This adds another level of indirection, I think. Currently cpu_to_node
is a simple inliner. After the patch it would be a real function with
all the associate overhead. Can you share a bloat-o-meter output here?
Regardless, I don't think that the approach is correct. As per your
description, some initialization functions erroneously call
cpu_to_node() instead of early_cpu_to_node() which exists specifically
for that case.
If the above correct, it's clearly a caller problem, and the fix is to
simply switch all those callers to use early version.
I would also initialize the numa_node with NUMA_NO_NODE at declaration,
so that if someone calls cpu_to_node() before the variable is properly
initialized at runtime, he'll get NO_NODE, which is obviously an error.
Thanks,
Yury
> Signed-off-by: Huang Shijie <shijie@...amperecomputing.com>
> ---
> drivers/base/arch_numa.c | 11 +++++++++++
> include/linux/topology.h | 6 ++----
> init/main.c | 29 +++++++++++++++++++++++++++--
> 3 files changed, 40 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/base/arch_numa.c b/drivers/base/arch_numa.c
> index 5b59d133b6af..867a477fa975 100644
> --- a/drivers/base/arch_numa.c
> +++ b/drivers/base/arch_numa.c
> @@ -61,6 +61,17 @@ EXPORT_SYMBOL(cpumask_of_node);
>
> #endif
>
> +#ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID
> +#ifndef cpu_to_node
> +int _cpu_to_node(int cpu)
> +{
> + return per_cpu(numa_node, cpu);
> +}
> +int (*cpu_to_node)(int cpu);
> +EXPORT_SYMBOL(cpu_to_node);
> +#endif
> +#endif
> +
> static void numa_update_cpu(unsigned int cpu, bool remove)
> {
> int nid = cpu_to_node(cpu);
> diff --git a/include/linux/topology.h b/include/linux/topology.h
> index 52f5850730b3..e7ce2bae11dd 100644
> --- a/include/linux/topology.h
> +++ b/include/linux/topology.h
> @@ -91,10 +91,8 @@ static inline int numa_node_id(void)
> #endif
>
> #ifndef cpu_to_node
> -static inline int cpu_to_node(int cpu)
> -{
> - return per_cpu(numa_node, cpu);
> -}
> +extern int (*cpu_to_node)(int cpu);
> +extern int _cpu_to_node(int cpu);
> #endif
>
> #ifndef set_numa_node
> diff --git a/init/main.c b/init/main.c
> index e24b0780fdff..b142e9c51161 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -870,6 +870,18 @@ static void __init print_unknown_bootoptions(void)
> memblock_free(unknown_options, len);
> }
>
> +static void __init smp_prepare_boot_cpu_start(void)
> +{
> + smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */
> +
> +#ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID
> +#ifndef cpu_to_node
> + /* The early_cpu_to_node should be ready now. */
> + cpu_to_node = early_cpu_to_node;
> +#endif
> +#endif
> +}
> +
> asmlinkage __visible __init __no_sanitize_address __noreturn __no_stack_protector
> void start_kernel(void)
> {
> @@ -899,7 +911,7 @@ void start_kernel(void)
> setup_command_line(command_line);
> setup_nr_cpu_ids();
> setup_per_cpu_areas();
> - smp_prepare_boot_cpu(); /* arch-specific boot-cpu hooks */
> + smp_prepare_boot_cpu_start();
> boot_cpu_hotplug_init();
>
> pr_notice("Kernel command line: %s\n", saved_command_line);
> @@ -1519,6 +1531,19 @@ void __init console_on_rootfs(void)
> fput(file);
> }
>
> +static void __init smp_prepare_cpus_done(unsigned int setup_max_cpus)
> +{
> + /* Different ARCHs may override smp_prepare_cpus() */
> + smp_prepare_cpus(setup_max_cpus);
> +
> +#ifdef CONFIG_USE_PERCPU_NUMA_NODE_ID
> +#ifndef cpu_to_node
> + /* Change to the formal function. */
> + cpu_to_node = _cpu_to_node;
> +#endif
> +#endif
> +}
> +
> static noinline void __init kernel_init_freeable(void)
> {
> /* Now the scheduler is fully set up and can do blocking allocations */
> @@ -1531,7 +1556,7 @@ static noinline void __init kernel_init_freeable(void)
>
> cad_pid = get_pid(t
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