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Subject: [PATCH v12 5/7] kexec: exclude hot remove cpu from elfcorehdr notes
Date:   Fri,  9 Sep 2022 17:05:07 -0400
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Due to use of CPUHP_AP_ONLINE_DYN, upon CPU unplug, the CPU is
still in the for_each_present_cpu() list when within the
handle_hotplug_event(). Thus the CPU must be explicitly excluded
when building the new list of CPUs.

This change identifies in handle_hotplug_event() the CPU to be
excluded, and the check for excluding the CPU in
crash_prepare_elf64_headers().

Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
Acked-by: Baoquan He <bhe@redhat.com>
---
 kernel/crash_core.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 4b15d91f0b21..5bc5159d9cb1 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -366,6 +366,11 @@ int crash_prepare_elf64_headers(struct kimage *image, struct crash_mem *mem,
 
 	/* Prepare one phdr of type PT_NOTE for each present CPU */
 	for_each_present_cpu(cpu) {
+#if defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+		/* Skip the soon-to-be offlined cpu */
+		if (image->hotplug_event && (cpu == image->offlinecpu))
+			continue;
+#endif
 		phdr->p_type = PT_NOTE;
 		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
 		phdr->p_offset = phdr->p_paddr = notes_addr;
@@ -682,6 +687,16 @@ static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
 		/* Flag to differentiate between normal load and hotplug */
 		image->hotplug_event = true;
 
+		/*
+		 * Due to use of CPUHP_AP_ONLINE_DYN, upon unplug and during
+		 * this callback, the CPU is still in the for_each_present_cpu()
+		 * list. Must explicitly look to exclude this CPU when building
+		 * new list.
+		 */
+		image->offlinecpu =
+			(hp_action == KEXEC_CRASH_HP_REMOVE_CPU) ?
+				cpu : KEXEC_CRASH_HP_INVALID_CPU;
+
 		/* Now invoke arch-specific update handler */
 		arch_crash_handle_hotplug_event(image, hp_action);
 
-- 
2.31.1