2022-02-09 20:49:02

by Eric DeVolder

Subject: [PATCH v4 08/10] crash hp: 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
crash_hotplug_handler(). Thus the CPU must be explicitly excluded
when building the new list of CPUs.

This change identifies in crash_hotplug_handler() 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 524470e18883..b6942e04a188 100644
--- a/kernel/crash_core.c
+++ b/kernel/crash_core.c
@@ -550,6 +550,16 @@ static void crash_hotplug_handler(unsigned int hp_action,
/* 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) ?
+ (unsigned int)a : ~0U;
+
/* Now invoke arch-specific update handler */
arch_crash_hotplug_handler(kexec_crash_image, hp_action, a, b);

diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index 93bb0c0ce66c..339995d42169 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) {
+#ifdef CONFIG_CRASH_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

2022-02-23 06:02:14

by Baoquan He

Subject: Re: [PATCH v4 08/10] crash hp: exclude hot remove cpu from elfcorehdr notes

On 02/09/22 at 02:57pm, 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
> crash_hotplug_handler(). Thus the CPU must be explicitly excluded
> when building the new list of CPUs.
>
> This change identifies in crash_hotplug_handler() the CPU to be
> excluded, and the check for excluding the CPU in
> crash_prepare_elf64_headers().

This looks good to me, and the particularity of cpu hotplug can be
understood well by other code reader. Thanks.

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

>
> 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 524470e18883..b6942e04a188 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -550,6 +550,16 @@ static void crash_hotplug_handler(unsigned int hp_action,
> /* 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) ?
> + (unsigned int)a : ~0U;
> +
> /* Now invoke arch-specific update handler */
> arch_crash_hotplug_handler(kexec_crash_image, hp_action, a, b);
>
> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> index 93bb0c0ce66c..339995d42169 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) {
> +#ifdef CONFIG_CRASH_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
>

2022-03-02 09:46:58

by Eric DeVolder

Subject: Re: [PATCH v4 08/10] crash hp: exclude hot remove cpu from elfcorehdr notes

On 2/22/22 22:04, Baoquan He wrote:
> On 02/09/22 at 02:57pm, 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
>> crash_hotplug_handler(). Thus the CPU must be explicitly excluded
>> when building the new list of CPUs.
>>
>> This change identifies in crash_hotplug_handler() the CPU to be
>> excluded, and the check for excluding the CPU in
>> crash_prepare_elf64_headers().
>
> This looks good to me, and the particularity of cpu hotplug can be
> understood well by other code reader. Thanks.
>
> Acked-by: Baoquan He <[email protected]>
Thank you!
eric
>
>>
>> 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 524470e18883..b6942e04a188 100644
>> --- a/kernel/crash_core.c
>> +++ b/kernel/crash_core.c
>> @@ -550,6 +550,16 @@ static void crash_hotplug_handler(unsigned int hp_action,
>> /* 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) ?
>> + (unsigned int)a : ~0U;
>> +
>> /* Now invoke arch-specific update handler */
>> arch_crash_hotplug_handler(kexec_crash_image, hp_action, a, b);
>>
>> diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
>> index 93bb0c0ce66c..339995d42169 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) {
>> +#ifdef CONFIG_CRASH_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
>>
>