[PATCH v7 2/8] x86/crash: Introduce new options to support cpu and memory hotplug

Borislav Petkov
2022-04-25T19:25:40Z

On Tue, Apr 19, 2022 at 04:58:47PM -0500, Eric DeVolder wrote:
> So in taking this concept and looking at, in particular, patch 4/8
> "crash: add generic infrastructure for crash hotplug support", I'm not
> exactly sure how to apply this technique.

So I took your patch 4 and maimed into what I think it should look like,
see below.

Now there's a single ifdef there and the registration routines are
wrapped in IS_ENABLED() so that you register a callback only when the
respective stuff - HOTPLUG_CPU or MEMORY_HOTPLUG - is enabled. Otherwise
the couple of functions are unused but that's not that big of a deal.

I've also fixed up some other issues I've encountered along the way.

Holler if there are questions.

HTH.

---
diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
index de62a722431e..b3c32e04d3f0 100644
--- a/include/linux/crash_core.h
+++ b/include/linux/crash_core.h
@@ -84,4 +84,12 @@ 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
+
+struct kimage;
+void arch_crash_handle_hotplug_event(struct kimage *image, unsigned int hp_action,
+ unsigned int cpu);
#endif /* LINUX_CRASH_CORE_H */
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 02daff1f47dd..d907a1f0d3da 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -307,13 +307,11 @@ 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
/* Virtual address of IMA measurement buffer for kexec syscall */
@@ -329,15 +327,6 @@ 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 ecf746243ab2..a6c4ee1d5c86 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -497,57 +497,50 @@ 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)
+void __weak arch_crash_handle_hotplug_event(struct kimage *image, unsigned int hp_action,
+ unsigned int cpu)
{
- pr_warn("crash hp: %s not implemented", __func__);
+ WARN(1, "crash hotplug handler not implemented");
}

-static void crash_hotplug_handler(unsigned int hp_action,
- unsigned int cpu)
+#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 */
- if (!mutex_trylock(&kexec_mutex))
+ if (!kexec_crash_image)
return;

- /* Check kdump is loaded */
- if (kexec_crash_image) {
- pr_debug("crash hp: hp_action %u, cpu %u", hp_action, cpu);
+ mutex_lock(&kexec_mutex);

- /* Needed in order for the segments to be updated */
- arch_kexec_unprotect_crashkres();
+ pr_debug("crash hotplug: hp_action %u, cpu %u", hp_action, cpu);

- /* Flag to differentiate between normal load and hotplug */
- kexec_crash_image->hotplug_event = true;
+ /* Needed in order for the segments to be updated */
+ arch_kexec_unprotect_crashkres();

- /* Now invoke arch-specific update handler */
- arch_crash_hotplug_handler(kexec_crash_image, hp_action, cpu);
+ /* Flag to differentiate between normal load and hotplug */
+ kexec_crash_image->hotplug_event = true;

- /* No longer handling a hotplug event */
- kexec_crash_image->hotplug_event = false;
+ /* Now invoke arch-specific update handler */
+ arch_crash_handle_hotplug_event(kexec_crash_image, hp_action, cpu);

- /* Change back to read-only */
- arch_kexec_protect_crashkres();
- }
+ /* 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)
+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);
+ handle_hotplug_event(KEXEC_CRASH_HP_ADD_MEMORY, -1U);
break;

case MEM_OFFLINE:
- crash_hotplug_handler(KEXEC_CRASH_HP_REMOVE_MEMORY, -1U);
+ handle_hotplug_event(KEXEC_CRASH_HP_REMOVE_MEMORY, -1U);
break;
}
return NOTIFY_OK;
@@ -557,38 +550,33 @@ 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);
+ handle_hotplug_event(KEXEC_CRASH_HP_ADD_CPU, cpu);
return 0;
}

static int crash_cpuhp_offline(unsigned int cpu)
{
- crash_hotplug_handler(KEXEC_CRASH_HP_REMOVE_CPU, cpu);
+ handle_hotplug_event(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 (IS_ENABLED(CONFIG_MEMORY_HOTPLUG))
+ register_memory_notifier(&crash_memhp_nb);

-#if defined(CONFIG_HOTPLUG_CPU)
- result = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
- "crash/cpuhp",
- crash_cpuhp_online, crash_cpuhp_offline);
-#endif
+ 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 /* CONFIG_CRASH_HOTPLUG */
+#endif

--
Regards/Gruss,
Boris.