linux-kernel - [PATCH v13 5/7] kexec: exclude hot remove cpu from elfcorehdr notes

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Message-Id: <20221031193604.28779-6-eric.devolder@oracle.com>
Date:   Mon, 31 Oct 2022 15:36:02 -0400
From:   Eric DeVolder <eric.devolder@...cle.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, ebiederm@...ssion.com,
        dyoung@...hat.com, bhe@...hat.com, vgoyal@...hat.com
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com,
        nramas@...ux.microsoft.com, thomas.lendacky@....com,
        robh@...nel.org, efault@....de, rppt@...nel.org, david@...hat.com,
        sourabhjain@...ux.ibm.com, konrad.wilk@...cle.com,
        boris.ostrovsky@...cle.com, eric.devolder@...cle.com
Subject: [PATCH v13 5/7] kexec: exclude hot remove cpu from elfcorehdr notes

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@...cle.com>
Acked-by: Baoquan He <bhe@...hat.com>
---
 kernel/crash_core.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 3a0ed4168fcd..bca1b198d9e5 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -366,6 +366,12 @@ 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 (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
+			/* Skip the soon-to-be offlined cpu */
+			if (image->hotplug_event && (cpu == image->offlinecpu))
+				continue;
+		}
+
 		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;
@@ -684,6 +690,16 @@ 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