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

Baoquan He
2022-08-08T09:30:20Z

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.

> +
> + /*
> + * 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
>