[PATCH v4 06/10] crash hp: generic crash hotplug support infrastructure

Eric DeVolder
2022-02-09T19:58:19Z

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.

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
---
kernel/crash_core.c | 104 ++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 104 insertions(+)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 0ff06d0698ad..524470e18883 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/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;
@@ -521,5 +525,105 @@ void unmap_crash_pages(void **ptr)
*ptr = NULL;
}
}
+
+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