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

[Eric DeVolder <eric.devolder@oracle.com>]

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 <bhe@redhat.com>
Thank you!
eric
> 
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
>> ---
>>   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
>>
>