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SubjectRe: [PATCH v5 4/8] crash: generic crash hotplug support infrastructure
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On 3/24/22 09:33, Baoquan He wrote:
> On 03/24/22 at 08:53am, Eric DeVolder wrote:
>> Baoquan,
>> Thanks, I've offered a minor correction below.
>> eric
>>
>> On 3/24/22 08:49, Baoquan He wrote:
>>> On 03/24/22 at 09:38pm, Baoquan He wrote:
>>>> On 03/03/22 at 11:27am, Eric DeVolder wrote:
>>>>> This patch introduces a generic crash hot plug/unplug infrastructure
>>>>> for CPU and memory changes. Upon CPU and memory changes, a generic
>>>>> crash_hotplug_handler() obtains the appropriate lock, does some
>>>>> important house keeping and then dispatches the hot plug/unplug event
>>>>> to the architecture specific arch_crash_hotplug_handler(), and when
>>>>> that handler returns, the lock is released.
>>>>>
>>>>> This patch modifies crash_core.c to implement a subsys_initcall()
>>>>> function that installs handlers for hot plug/unplug events. If CPU
>>>>> hotplug is enabled, then cpuhp_setup_state() is invoked to register a
>>>>> handler for CPU changes. Similarly, if memory hotplug is enabled, then
>>>>> register_memory_notifier() is invoked to install a handler for memory
>>>>> changes. These handlers in turn invoke the common generic handler
>>>>> crash_hotplug_handler().
>>>>>
>>>>> On the CPU side, cpuhp_setup_state_nocalls() is invoked with parameter
>>>>> CPUHP_AP_ONLINE_DYN. While this works, when a CPU is being unplugged,
>>>>> the CPU still shows up in foreach_present_cpu() during the regeneration
>>>>> of the new CPU list, thus the need to explicitly check and exclude the
>>>>> soon-to-be offlined CPU in crash_prepare_elf64_headers().
>>>>>
>>>>> On the memory side, each un/plugged memory block passes through the
>>>>> handler. For example, if a 1GiB DIMM is hotplugged, that generate 8
>>>>> memory events, one for each 128MiB memblock.
>>>>
>>>> I rewrite the log as below with my understanding. Hope it's simpler to
>>>> help people get what's going on here. Please consider to take if it's
>>>> OK to you or adjust based on this. The code looks good to me.
>>>>
>>> Made some tuning:
>>>
>>> crash: add generic infrastructure for crash hotplug support
>>>
>>> Upon CPU and memory changes, a generic crash_hotplug_handler() is added
>>> to dispatch the hot plug/unplug event to the architecture specific
>>> arch_crash_hotplug_handler(). During the process, kexec_mutex need be
>>> held.
>>>
>>> To support cpu hotplug, one callback pair are registered to capture
>>> KEXEC_CRASH_HP_ADD_CPU and KEXEC_CRASH_HP_REMOVE_CPU events via
>>> cpuhp_setup_state_nocalls().
>> s/KEXEC_CRASH_HP_ADD}REMOVE_CPU/CPUHP_AP_ONLINE_DYN/ as the KEXEC_CRASH are the
>> names I've introduced with this patch?
>
> Right.
>
> While checking it, I notice hp_action which you don't use actually.
> Can you reconsider that part of design, the hp_action, the a, b
> parameter passed to handler?

Sure I can remove. I initially put in there as this was generic infrastructure and not sure if it
would benefit others.
eric

>
>>
>>>
>>> To support memory hotplug, a notifier crash_memhp_nb is registered to
>>> memory_chain to watch MEM_ONLINE and MEM_OFFLINE events.
>>>
>>> These callbacks and notifier will call crash_hotplug_handler() to handle
>>> captured event when invoked.
>>>
>>>>
>>>>>
>>>>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
>>>>> ---
>>>>> include/linux/kexec.h | 16 +++++++
>>>>> kernel/crash_core.c | 108 ++++++++++++++++++++++++++++++++++++++++++
>>>>> 2 files changed, 124 insertions(+)
>>>>>
>>>>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>>>>> index d7b59248441b..b11d75a6b2bc 100644
>>>>> --- a/include/linux/kexec.h
>>>>> +++ b/include/linux/kexec.h
>>>>> @@ -300,6 +300,13 @@ struct kimage {
>>>>> /* Information for loading purgatory */
>>>>> struct purgatory_info purgatory_info;
>>>>> +
>>>>> +#ifdef CONFIG_CRASH_HOTPLUG
>>>>> + bool hotplug_event;
>>>>> + int offlinecpu;
>>>>> + bool elf_index_valid;
>>>>> + int elf_index;
>>>>> +#endif
>>>>> #endif
>>>>> #ifdef CONFIG_IMA_KEXEC
>>>>> @@ -316,6 +323,15 @@ struct kimage {
>>>>> unsigned long elf_load_addr;
>>>>> };
>>>>> +#ifdef CONFIG_CRASH_HOTPLUG
>>>>> +void arch_crash_hotplug_handler(struct kimage *image,
>>>>> + unsigned int hp_action, unsigned long a, unsigned long b);
>>>>> +#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..76959d440f71 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 +496,106 @@ 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 long a, unsigned long b)
>>>>> +{
>>>>> + pr_warn("crash hp: %s not implemented", __func__);
>>>>> +}
>>>>> +
>>>>> +static void crash_hotplug_handler(unsigned int hp_action,
>>>>> + unsigned long a, unsigned long b)
>>>>> +{
>>>>> + /* 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, a %lu, b %lu", hp_action,
>>>>> + a, b);
>>>>> +
>>>>> + /* 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, a, b);
>>>>> +
>>>>> + /* 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;
>>>>> + unsigned long start, end;
>>>>> +
>>>>> + start = mhp->start_pfn << PAGE_SHIFT;
>>>>> + end = ((mhp->start_pfn + mhp->nr_pages) << PAGE_SHIFT) - 1;
>>>>> +
>>>>> + switch (val) {
>>>>> + case MEM_ONLINE:
>>>>> + crash_hotplug_handler(KEXEC_CRASH_HP_ADD_MEMORY,
>>>>> + start, end-start);
>>>>> + break;
>>>>> +
>>>>> + case MEM_OFFLINE:
>>>>> + crash_hotplug_handler(KEXEC_CRASH_HP_REMOVE_MEMORY,
>>>>> + start, end-start);
>>>>> + 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, 0);
>>>>> + return 0;
>>>>> +}
>>>>> +
>>>>> +static int crash_cpuhp_offline(unsigned int cpu)
>>>>> +{
>>>>> + crash_hotplug_handler(KEXEC_CRASH_HP_REMOVE_CPU, cpu, 0);
>>>>> + 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
>>>>>
>>>>
>>>
>>
>

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