[PATCH v7 4/8] crash: add generic infrastructure for crash hotplug support

Baoquan He
2022-04-14T02:45:48Z

On 04/13/22 at 12:42pm, Eric DeVolder wrote:
> Upon CPU and memory changes, a generic crash_hotplug_handler()
> dispatches the hot plug/unplug event to the architecture specific
> arch_crash_hotplug_handler(). During the process, the kexec_mutex
> is held.
>
> To support cpu hotplug, a callback is registered to capture the
> CPUHP_AP_ONLINE_DYN online and ofline events via
> cpuhp_setup_state_nocalls().
>
> To support memory hotplug, a notifier is registered to capture the
> MEM_ONLINE and MEM_OFFLINE events via register_memory_notifier().
>
> The cpu callback and memory notifier then call crash_hotplug_handler()
> to handle the hot plug/unplug event.
>
> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
> ---
> include/linux/kexec.h | 16 +++++++
> kernel/crash_core.c | 101 ++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 117 insertions(+)
>
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index f93f2591fc1e..02daff1f47dd 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -306,6 +306,13 @@ struct kimage {
>
> /* Information for loading purgatory */
> struct purgatory_info purgatory_info;
> +
> +#ifdef CONFIG_CRASH_HOTPLUG
> + bool hotplug_event;
> + unsigned int offlinecpu;
> + bool elfcorehdr_index_valid;
> + int elfcorehdr_index;
> +#endif
> #endif
>
> #ifdef CONFIG_IMA_KEXEC
> @@ -322,6 +329,15 @@ struct kimage {
> unsigned long elf_load_addr;
> };
>
> +#ifdef CONFIG_CRASH_HOTPLUG
> +void arch_crash_hotplug_handler(struct kimage *image,
> + unsigned int hp_action, unsigned int cpu);
> +#define KEXEC_CRASH_HP_REMOVE_CPU 0
> +#define KEXEC_CRASH_HP_ADD_CPU 1
> +#define KEXEC_CRASH_HP_REMOVE_MEMORY 2
> +#define KEXEC_CRASH_HP_ADD_MEMORY 3
> +#endif /* CONFIG_CRASH_HOTPLUG */
> +
> /* kexec interface functions */
> extern void machine_kexec(struct kimage *image);
> extern int machine_kexec_prepare(struct kimage *image);
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 256cf6db573c..ecf746243ab2 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -9,12 +9,17 @@
> #include <linux/init.h>
> #include <linux/utsname.h>
> #include <linux/vmalloc.h>
> +#include <linux/highmem.h>
> +#include <linux/memory.h>
> +#include <linux/cpuhotplug.h>
>
> #include <asm/page.h>
> #include <asm/sections.h>
>
> #include <crypto/sha1.h>
>
> +#include "kexec_internal.h"
> +
> /* vmcoreinfo stuff */
> unsigned char *vmcoreinfo_data;
> size_t vmcoreinfo_size;
> @@ -491,3 +496,99 @@ static int __init crash_save_vmcoreinfo_init(void)
> }
>
> subsys_initcall(crash_save_vmcoreinfo_init);
> +
> +#ifdef CONFIG_CRASH_HOTPLUG
> +void __weak arch_crash_hotplug_handler(struct kimage *image,
> + unsigned int hp_action, unsigned int cpu)
> +{
> + pr_warn("crash hp: %s not implemented", __func__);
> +}
> +
> +static void crash_hotplug_handler(unsigned int hp_action,
> + unsigned int cpu)
> +{
> + /* Obtain lock while changing crash information */
> + if (!mutex_trylock(&kexec_mutex))
> + return;
> +
> + /* Check kdump is loaded */
> + if (kexec_crash_image) {
> + pr_debug("crash hp: hp_action %u, cpu %u", hp_action, cpu);
> +
> + /* Needed in order for the segments to be updated */
> + arch_kexec_unprotect_crashkres();
> +
> + /* Flag to differentiate between normal load and hotplug */
> + kexec_crash_image->hotplug_event = true;
> +
> + /* Now invoke arch-specific update handler */
> + arch_crash_hotplug_handler(kexec_crash_image, hp_action, cpu);
> +
> + /* No longer handling a hotplug event */
> + kexec_crash_image->hotplug_event = false;
> +
> + /* Change back to read-only */
> + arch_kexec_protect_crashkres();
> + }
> +
> + /* Release lock now that update complete */
> + mutex_unlock(&kexec_mutex);
> +}
> +
> +#if defined(CONFIG_MEMORY_HOTPLUG)
> +static int crash_memhp_notifier(struct notifier_block *nb,
> + unsigned long val, void *v)
> +{
> + struct memory_notify *mhp = v;
> +
> + switch (val) {
> + case MEM_ONLINE:
> + crash_hotplug_handler(KEXEC_CRASH_HP_ADD_MEMORY, -1U);
We don't differentiate the memory add/remove, cpu add, except of cpu
remove. Means the hp_action only differentiate cpu remove from the other
action. Maybe only making two types?

#define KEXEC_CRASH_HP_REMOVE_CPU 0
#define KEXEC_CRASH_HP_UPDATE_OTHER 1

And define a new macro to replace the magic number?

#define KEXEC_CRASH_HP_INVALID_CPU -1U
> + break;
> +
> + case MEM_OFFLINE:
> + crash_hotplug_handler(KEXEC_CRASH_HP_REMOVE_MEMORY, -1U);
> + break;
> + }
> + return NOTIFY_OK;
> +}
> +
> +static struct notifier_block crash_memhp_nb = {
> + .notifier_call = crash_memhp_notifier,
> + .priority = 0
> +};
> +#endif
> +
> +#if defined(CONFIG_HOTPLUG_CPU)
> +static int crash_cpuhp_online(unsigned int cpu)
> +{
> + crash_hotplug_handler(KEXEC_CRASH_HP_ADD_CPU, cpu);
Should making the cpu as -1U?
crash_hotplug_handler(KEXEC_CRASH_HP_ADD_CPU, -1U);
> + return 0;
> +}
> +
> +static int crash_cpuhp_offline(unsigned int cpu)
> +{
> + crash_hotplug_handler(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
> + return 0;
> +}
> +#endif
> +
> +static int __init crash_hotplug_init(void)
> +{
> + int result = 0;
> +
> +#if defined(CONFIG_MEMORY_HOTPLUG)
> + register_memory_notifier(&crash_memhp_nb);
> +#endif
> +
> +#if defined(CONFIG_HOTPLUG_CPU)
> + result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
> + "crash/cpuhp",
> + crash_cpuhp_online, crash_cpuhp_offline);
> +#endif
> +
> + return result;
> +}
> +
> +subsys_initcall(crash_hotplug_init);
> +#endif /* CONFIG_CRASH_HOTPLUG */
> --
> 2.27.0
>