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

Eric DeVolder
2022-04-14T22:30:37Z

Hi Baoquan,
Inline comments below.
Thanks!
eric

On 4/13/22 21:45, Baoquan He wrote:
> 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
>
Sourabh Jain's work with PPC uses REMOVE_CPU, REMOVE_MEMORY, and ADD_MEMORY.
Do you still want to consolidate these?

> And define a new macro to replace the magic number?
Yes, I will do this.

>
> #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?
Well, the cpu would be correct/valid cpu. Is there harm in reporting it?

> 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
>>
>