linux-kernel - Re: [PATCH v25 06/10] crash: memory and CPU hotplug sysfs attributes

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Date:   Thu, 29 Jun 2023 17:31:33 -0500
From:   Eric DeVolder <eric.devolder@...cle.com>
To:     Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org,
        david@...hat.com, osalvador@...e.de, corbet@....net,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, bhe@...hat.com,
        ebiederm@...ssion.com, kexec@...ts.infradead.org
Cc:     hpa@...or.com, gregkh@...uxfoundation.org, rafael@...nel.org,
        vgoyal@...hat.com, dyoung@...hat.com, lf32.dev@...il.com,
        akpm@...ux-foundation.org, naveen.n.rao@...ux.vnet.ibm.com,
        zohar@...ux.ibm.com, bhelgaas@...gle.com, vbabka@...e.cz,
        tiwai@...e.de, seanjc@...gle.com, linux@...ssschuh.net,
        vschneid@...hat.com, linux-mm@...ck.org, linux-doc@...r.kernel.org,
        sourabhjain@...ux.ibm.com, konrad.wilk@...cle.com,
        boris.ostrovsky@...cle.com
Subject: Re: [PATCH v25 06/10] crash: memory and CPU hotplug sysfs attributes

Randy,
Thanks for looking at this! Inline comments below.
eric

On 6/29/23 15:59, Randy Dunlap wrote:
> Hi--
> 
> On 6/29/23 12:21, Eric DeVolder wrote:
>>
>> Signed-off-by: Eric DeVolder <eric.devolder@...cle.com>
>> Reviewed-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
>> Acked-by: Hari Bathini <hbathini@...ux.ibm.com>
>> Acked-by: Baoquan He <bhe@...hat.com>
>> ---
>>   Documentation/ABI/testing/sysfs-devices-memory |  8 ++++++++
>>   .../ABI/testing/sysfs-devices-system-cpu       |  8 ++++++++
>>   .../admin-guide/mm/memory-hotplug.rst          |  8 ++++++++
>>   Documentation/core-api/cpu_hotplug.rst         | 18 ++++++++++++++++++
>>   drivers/base/cpu.c                             | 16 ++++++++++++++--
>>   drivers/base/memory.c                          | 13 +++++++++++++
>>   include/linux/kexec.h                          |  8 ++++++++
>>   7 files changed, 77 insertions(+), 2 deletions(-)
>>
> 
>> diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
>> index 1b02fe5807cc..eb99d79223a3 100644
>> --- a/Documentation/admin-guide/mm/memory-hotplug.rst
>> +++ b/Documentation/admin-guide/mm/memory-hotplug.rst
>> @@ -291,6 +291,14 @@ The following files are currently defined:
>>   		       Availability depends on the CONFIG_ARCH_MEMORY_PROBE
>>   		       kernel configuration option.
>>   ``uevent``	       read-write: generic udev file for device subsystems.
>> +``crash_hotplug``      read-only: when changes to the system memory map
>> +		       occur due to hot un/plug of memory, this file contains
>> +		       '1' if the kernel updates the kdump capture kernel memory
>> +		       map itself (via elfcorehdr), or '0' if userspace must update
>> +		       the kdump capture kernel memory map.
>> +
>> +		       Availability depends on the CONFIG_MEMORY_HOTPLUG kernel
>> +		       configuration option.
>>   ====================== =========================================================
> 
> Did you test build the documentation?
> It looks to me like the end-of-table '=' signs line needs 3 more === to be long
> enough for the text above it.

Hmm, the 'make htmldocs' renders and views ok. Is there perhaps another method I should use?

> 
>>   
>>   .. note::
>> diff --git a/Documentation/core-api/cpu_hotplug.rst b/Documentation/core-api/cpu_hotplug.rst
>> index e6f5bc39cf5c..54581c501562 100644
>> --- a/Documentation/core-api/cpu_hotplug.rst
>> +++ b/Documentation/core-api/cpu_hotplug.rst
>> @@ -741,6 +741,24 @@ will receive all events. A script like::
>>   
>>   can process the event further.
>>   
>> +When changes to the CPUs in the system occur, the sysfs file
>> +/sys/devices/system/cpu/crash_hotplug contains '1' if the kernel
>> +updates the kdump capture kernel list of CPUs itself (via elfcorehdr),
>> +or '0' if userspace must update the kdump capture kernel list of CPUs.
>> +
>> +The availability depends on the CONFIG_HOTPLUG_CPU kernel configuration
>> +option.
>> +
>> +To skip userspace processing of CPU hot un/plug events for kdump
>> +(ie the unload-then-reload to obtain a current list of CPUs), this sysfs
> 
>      i.e.
> 
got it, thanks.

>> +file can be used in a udev rule as follows:
>> +
>> + SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
>> +
>> +For a cpu hot un/plug event, if the architecture supports kernel updates
> 
>           CPU
> for consistency
> 
got it, thanks.

>> +of the elfcorehdr (which contains the list of CPUs), then the rule skips
>> +the unload-then-reload of the kdump capture kernel.
>> +
>>   Kernel Inline Documentations Reference
>>   ======================================
>>   
> 
> Thanks.