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

[Eric DeVolder]

On 2/22/22 21:59, Baoquan He wrote:

On 02/09/22 at 02:57pm, 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.

This looks good to me. As I commented in patch 3, these both may need be
merged.

OK, merged with 3.
eric

Signed-off-by: Eric DeVolder <eric.devol...@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

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