[PATCH v7 4/8] crash: add phdr for possible CPUs in elfcorehdr

[Sourabh Jain]

On architectures like PowerPC the crash notes are available for all
possible CPUs. So let's populate the elfcorehdr for all possible
CPUs having crash notes to avoid updating elfcorehdr during in-kernel
crash update on CPU hotplug events.

The similar technique is used in kexec-tool for kexec_load case.

Signed-off-by: Sourabh Jain <sourabhjain at linux.ibm.com>
---
 kernel/crash_core.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index 910d377ea317e..19f987b3851e8 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -364,8 +364,8 @@ int crash_prepare_elf64_headers(struct kimage *image, struct crash_mem *mem,
 	ehdr->e_ehsize = sizeof(Elf64_Ehdr);
 	ehdr->e_phentsize = sizeof(Elf64_Phdr);
 
-	/* Prepare one phdr of type PT_NOTE for each present CPU */
-	for_each_present_cpu(cpu) {
+	/* Prepare one phdr of type PT_NOTE for possible CPU with crash note. */
+	for_each_possible_cpu(cpu) {
 #ifdef CONFIG_CRASH_HOTPLUG
 		if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
 			/* Skip the soon-to-be offlined cpu */
@@ -373,8 +373,11 @@ int crash_prepare_elf64_headers(struct kimage *image, struct crash_mem *mem,
 				continue;
 		}
 #endif
-		phdr->p_type = PT_NOTE;
 		notes_addr = per_cpu_ptr_to_phys(per_cpu_ptr(crash_notes, cpu));
+		if (!notes_addr)
+			continue;
+
+		phdr->p_type = PT_NOTE;
 		phdr->p_offset = phdr->p_paddr = notes_addr;
 		phdr->p_filesz = phdr->p_memsz = sizeof(note_buf_t);
 		(ehdr->e_phnum)++;
-- 
2.39.0