On 02/02/23 21:07, Eric DeVolder wrote:
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.
I was in the impression that if CPU notes are missing for offline CPUs
in the elfcorehdr then makedumpfile will mess up the
CPU IDs.
But somehow replacing for_each_present_cpu with for_each_online_cpu
worked on PowerPC, even after disabling a couple of CPUs.
So things are fine if we pack PT_LOAD for online CPUs instead of present
CPUs but,
I need to investigate how makedumpfile is able to map PT_LOAD to online
CPUs.
- Sourabh Jain
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