2022-05-06 16:11:41

by Eric DeVolder

Subject: [PATCH v8 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 <[email protected]>
---
kernel/crash_core.c | 10 ++++++++++
kernel/kexec_file.c | 5 +++++
2 files changed, 15 insertions(+)

diff --git a/kernel/crash_core.c b/kernel/crash_core.c
index f197af50def6..7ba43f058d82 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -520,6 +520,16 @@ static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
/* Flag to differentiate between normal load and hotplug */
kexec_crash_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.
+ */
+ kexec_crash_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(kexec_crash_image, hp_action, cpu);

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index aacdf93c3507..d68e5769b428 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -1314,6 +1314,11 @@ 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 defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
+ /* Skip the soon-to-be offlined cpu */
+ if (image->hotplug_event && (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;
--
2.27.0

2022-05-11 22:07:23

by Baoquan He

Subject: Re: [PATCH v8 5/7] kexec: exclude hot remove cpu from elfcorehdr notes

On 05/05/22 at 02:46pm, Eric DeVolder wrote:
> 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 <[email protected]>

LGTM,

Acked-by: Baoquan He <[email protected]>

> ---
> kernel/crash_core.c | 10 ++++++++++
> kernel/kexec_file.c | 5 +++++
> 2 files changed, 15 insertions(+)
>
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index f197af50def6..7ba43f058d82 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -520,6 +520,16 @@ static void handle_hotplug_event(unsigned int hp_action, unsigned int cpu)
> /* Flag to differentiate between normal load and hotplug */
> kexec_crash_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.
> + */
> + kexec_crash_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(kexec_crash_image, hp_action, cpu);
>
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index aacdf93c3507..d68e5769b428 100644
> --- a/kernel/kexec_file.c
> +++ b/kernel/kexec_file.c
> @@ -1314,6 +1314,11 @@ 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 defined(CONFIG_HOTPLUG_CPU) || defined(CONFIG_MEMORY_HOTPLUG)
> + /* Skip the soon-to-be offlined cpu */
> + if (image->hotplug_event && (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;
> --
> 2.27.0
>