Re: [PATCH v10 4/8] crash: add generic infrastructure for crash hotplug support

Eric DeVolder
2022-08-08T15:21:05Z

On 8/8/22 04:30, Baoquan He wrote:
> On 07/21/22 at 02:17pm, Eric DeVolder wrote:
>> CPU and memory change notifications are received in order to
>> regenerate the elfcorehdr.
>>
>> To support cpu hotplug, a callback is registered to capture the
>> CPUHP_AP_ONLINE_DYN online and offline 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 notifiers call handle_hotplug_event()
>> which performs needed tasks and then dispatches the event to the
>> architecture specific arch_crash_handle_hotplug_event(). During the
>> process, the kexec_mutex is held.
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
>> ---
>> include/linux/crash_core.h | 24 ++++++++
>> include/linux/kexec.h | 7 +++
>> kernel/crash_core.c | 118 +++++++++++++++++++++++++++++++++++++
>> 3 files changed, 149 insertions(+)
>>
>> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
>> index cb0f1916fbf5..c9705b6872e7 100644
>> --- a/include/linux/crash_core.h
>> +++ b/include/linux/crash_core.h
>> @@ -86,4 +86,28 @@ int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
>> int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
>> unsigned long long *crash_size, unsigned long long *crash_base);
>>
>> +#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
>> +#define KEXEC_CRASH_HP_INVALID_CPU -1U
>> +
>> +struct kimage;
>> +#ifndef arch_map_crash_pages
>> +static inline void *arch_map_crash_pages(unsigned long paddr,
>> + unsigned long size)
>> +{
>> + return NULL;
>> +}
>> +#endif
>> +#ifndef arch_unmap_crash_pages
>> +static inline void arch_unmap_crash_pages(void **ptr) { }
>> +#endif
>> +#ifndef arch_crash_handle_hotplug_event
>> +static inline void arch_crash_handle_hotplug_event(struct kimage *image,
>> + unsigned int hp_action, unsigned int cpu)
>> +{
>> +}
>> +#endif
>> +
>> #endif /* LINUX_CRASH_CORE_H */
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index 5f4969cf3f4e..7694aa77b92b 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -340,6 +340,13 @@ struct kimage {
>> struct purgatory_info purgatory_info;
>> #endif
>>
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> + bool hotplug_event;
>> + unsigned int offlinecpu;
>> + bool elfcorehdr_index_valid;
>> + int elfcorehdr_index;
>> +#endif
>> +
>> #ifdef CONFIG_IMA_KEXEC
>> /* Virtual address of IMA measurement buffer for kexec syscall */
>> void *ima_buffer;
>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>> index 212d4dad0ec7..154ef532d45a 100644
>> --- a/kernel/crash_core.c
>> +++ b/kernel/crash_core.c
>> @@ -10,12 +10,16 @@
>> #include <linux/utsname.h>
>> #include <linux/vmalloc.h>
>> #include <linux/kexec.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;
>> @@ -587,3 +591,117 @@ static int __init crash_save_vmcoreinfo_init(void)
>> }
>>
>> subsys_initcall(crash_save_vmcoreinfo_init);
>> +
>> +#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
>> +static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
>> +{
>> + /* Obtain lock while changing crash information */
>> + mutex_lock(&kexec_mutex);
>> +
>> + /* Check kdump is loaded */
>> + if (kexec_crash_image) {
>> + struct kimage *image = kexec_crash_image;
>> +
>> + pr_debug("crash hp: hp_action %u, cpu %u", hp_action, cpu);
>
> We don't need to check if it's cpu hotplug action here? Then for mem
> hotplug actions, we also get:
> "crash hp: hp_action 2, cpu 0"
> That cpu 0 will be confusing. And you forgot the line break.
>
> Can we do like this:
> pr_debug("crash hp: hp_action %u ", hp_action);
> if (hp_action == KEXEC_CRASH_HP_REMOVE_CPU ||
> hp_action == KEXEC_CRASH_HP_REMOVE_CPU)
> pr_debug("cpu %u \n", cpu);
>
> Other than this, the patch looks good to me.

OK, I'll make the changes you suggest, thanks!
eric

>
>> +
>> + /*
>> + * When the struct kimage is alloced, it is wiped to zero, so
>> + * the elfcorehdr_index_valid defaults to false. Find the
>> + * segment containing the elfcorehdr, if not already found.
>> + * This works for both the kexec_load and kexec_file_load paths.
>> + */
>> + if (!image->elfcorehdr_index_valid) {
>> + unsigned char *ptr;
>> + unsigned long mem, memsz;
>> + unsigned int n;
>> +
>> + for (n = 0; n < image->nr_segments; n++) {
>> + mem = image->segment[n].mem;
>> + memsz = image->segment[n].memsz;
>> + ptr = arch_map_crash_pages(mem, memsz);
>> + if (ptr) {
>> + /* The segment containing elfcorehdr */
>> + if (memcmp(ptr, ELFMAG, SELFMAG) == 0) {
>> + image->elfcorehdr_index = (int)n;
>> + image->elfcorehdr_index_valid = true;
>> + }
>> + }
>> + arch_unmap_crash_pages((void **)&ptr);
>> + }
>> + }
>> +
>> + if (!image->elfcorehdr_index_valid) {
>> + pr_err("crash hp: unable to locate elfcorehdr segment");
>> + goto out;
>> + }
>> +
>> + /* Needed in order for the segments to be updated */
>> + arch_kexec_unprotect_crashkres();
>> +
>> + /* Flag to differentiate between normal load and hotplug */
>> + image->hotplug_event = true;
>> +
>> + /* Now invoke arch-specific update handler */
>> + arch_crash_handle_hotplug_event(image, hp_action, cpu);
>> +
>> + /* No longer handling a hotplug event */
>> + image->hotplug_event = false;
>> +
>> + /* Change back to read-only */
>> + arch_kexec_protect_crashkres();
>> + }
>> +
>> +out:
>> + /* Release lock now that update complete */
>> + mutex_unlock(&kexec_mutex);
>> +}
>> +
>> +static int crash_memhp_notifier(struct notifier_block *nb, unsigned long val, void *v)
>> +{
>> + switch (val) {
>> + case MEM_ONLINE:
>> + handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY, 0);
>> + break;
>> +
>> + case MEM_OFFLINE:
>> + handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY, 0);
>> + break;
>> + }
>> + return NOTIFY_OK;
>> +}
>> +
>> +static struct notifier_block crash_memhp_nb = {
>> + .notifier_call = crash_memhp_notifier,
>> + .priority = 0
>> +};
>> +
>> +static int crash_cpuhp_online(unsigned int cpu)
>> +{
>> + handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu);
>> + return 0;
>> +}
>> +
>> +static int crash_cpuhp_offline(unsigned int cpu)
>> +{
>> + handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
>> + return 0;
>> +}
>> +
>> +static int __init crash_hotplug_init(void)
>> +{
>> + int result = 0;
>> +
>> + if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
>> + register_memory_notifier(&crash_memhp_nb);
>> +
>> + if (IS_ENABLED(CONFIG_HOTPLUG_CPU))
>> + result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
>> + "crash/cpuhp",
>> + crash_cpuhp_online,
>> + crash_cpuhp_offline);
>> +
>> + return result;
>> +}
>> +
>> +subsys_initcall(crash_hotplug_init);
>> +#endif
>> --
>> 2.31.1
>>
>