linux-kernel - [PATCH v18 5/7] kexec: exclude hot remove cpu from elfcorehdr notes

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Message-Id: <20230131224236.122805-6-eric.devolder@oracle.com>
Date:   Tue, 31 Jan 2023 17:42:34 -0500
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 v18 5/7] kexec: exclude hot remove cpu from elfcorehdr notes

In crash_prepare_elf64_headers(), the for_each_present_cpu() is
utilized to create the new elfcorehdr. When handling CPU hot
unplug/offline events, the CPU is still on the for_each_present_cpu()
list (not until the cpuhp state processing reaches CPUHP_OFFLINE does
the CPU exit the list). 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 5545de4597d0..d985d334fae4 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -366,6 +366,14 @@ 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) {
+#ifdef CONFIG_CRASH_HOTPLUG
+		if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
+			/* Skip the soon-to-be offlined cpu */
+			if ((image->hp_action == KEXEC_CRASH_HP_REMOVE_CPU) &&
+				(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;
@@ -769,6 +777,14 @@ static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
 			/* Differentiate between normal load and hotplug update */
 			image->hp_action = hp_action;
 
+			/*
+			 * Record which CPU is being unplugged/offlined, so that it
+			 * is explicitly excluded in crash_prepare_elf64_headers().
+			 */
+			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);
 
-- 
2.31.1