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

[Eric DeVolder]

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.devol...@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

_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec