On 2/1/23 00:38, Sourabh Jain wrote:
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@xxxxxxxxxxxxx>
---
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 37c594858fd51..898d8d2fe2e2e 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) {
Sourabh,
Thomas Gleixner is suggesting moving away from for_each_present_cpu() to for_each_online_cpu().
Using for_each_online_cpu() is going to the minimum number of needed, whereas your approach of
for_each_possible_cpu() would be to the maximum number needed.
What would be the ramifications to ppc for moving towards for_each_online_cpu()?
In my next patch series, I have finally figured out how to use cpuhp framework to where it is
possible to use for_each_online_cpu() here, but that is at odds with your changes here.
Thanks,
eric
#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)++;
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