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From: Thomas Gleixner <tglx@linutronix.de>
To: Sourabh Jain <sourabhjain@linux.ibm.com>,
	Eric DeVolder <eric.devolder@oracle.com>,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	kexec@lists.infradead.org, ebiederm@xmission.com,
	dyoung@redhat.com, bhe@redhat.com, vgoyal@redhat.com
Cc: mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
	hpa@zytor.com, nramas@linux.microsoft.com,
	thomas.lendacky@amd.com, robh@kernel.org, efault@gmx.de,
	rppt@kernel.org, david@redhat.com, konrad.wilk@oracle.com,
	boris.ostrovsky@oracle.com
Subject: Re: [PATCH v18 5/7] kexec: exclude hot remove cpu from elfcorehdr notes
Date: Mon, 06 Feb 2023 14:03:28 +0100	[thread overview]
Message-ID: <87357jymhr.ffs@tglx> (raw)
In-Reply-To: <8308e930-6b55-5756-d653-5c623a8ea758@linux.ibm.com>

On Mon, Feb 06 2023 at 13:42, Sourabh Jain wrote:
> On 01/02/23 17:03, Thomas Gleixner wrote:
>> Also in case of loading the crash kernel in the situation where not all
>> present CPUs are online (think boot time SMT disable) then your
>> resulting crash image will contain all present CPUs and none of the
>> offline CPUs are excluded.
>>
>> How does that make any sense at all?
>>
>> This image->hp_action and image->offlinecpu dance is engineering
>> voodoo. You just can do:
>>
>>          for_each_present_cpu(cpu) {
>>              if (!cpu_online(cpu))
>>              	continue;
>>              do_stuff(cpu);
>>
>> which does the right thing in all situations and can be further
>> simplified to:
>>
>>          for_each_online_cpu(cpu) {
>>              do_stuff(cpu);
>
> What will be the implication on x86 if we pack PT_NOTE for possible
> CPUs?

I don't know.

> IIUC, on boot the crash notes are create for possible CPUs using pcpu_alloc
> and when the system is on crash path the crash notes for online CPUs is
> populated with the required data and rest crash notes are untouched.

Which should be fine. That's a problem of postprocessing and it's
unclear to me from the changelogs what the actual problem is which is
trying to be solved here.

Thanks,

        tglx



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  reply	other threads:[~2023-02-06 13:03 UTC|newest]

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-31 22:42 [PATCH v18 0/7] crash: Kernel handling of CPU and memory hot un/plug Eric DeVolder
2023-01-31 22:42 ` [PATCH v18 1/7] crash: move a few code bits to setup support of crash hotplug Eric DeVolder
2023-01-31 22:42 ` [PATCH v18 2/7] crash: prototype change for crash_prepare_elf64_headers() Eric DeVolder
2023-01-31 22:42 ` [PATCH v18 3/7] crash: add generic infrastructure for crash hotplug support Eric DeVolder
2023-02-09 19:10   ` Sourabh Jain
2023-02-10 16:51     ` Eric DeVolder
2023-01-31 22:42 ` [PATCH v18 4/7] kexec: exclude elfcorehdr from the segment digest Eric DeVolder
2023-01-31 22:42 ` [PATCH v18 5/7] kexec: exclude hot remove cpu from elfcorehdr notes Eric DeVolder
2023-02-01 11:33   ` Thomas Gleixner
2023-02-06  8:12     ` Sourabh Jain
2023-02-06 13:03       ` Thomas Gleixner [this message]
2023-02-07 17:23     ` Eric DeVolder
2023-02-08 13:44       ` Thomas Gleixner
2023-02-09 17:31         ` Eric DeVolder
2023-02-09 18:43           ` Sourabh Jain
2023-02-09 19:39             ` Eric DeVolder
2023-02-10  6:29               ` Sourabh Jain
2023-02-11  0:35                 ` Eric DeVolder
2023-02-13  4:40                   ` Sourabh Jain
2023-02-13 12:52                     ` Thomas Gleixner
2023-02-15  2:53                       ` Sourabh Jain
2023-02-28 12:44                     ` Baoquan He
2023-02-28 18:52                       ` Eric DeVolder
2023-03-01 15:48                         ` Eric DeVolder
2023-03-02 10:51                           ` Baoquan He
2023-03-02  5:23                         ` Sourabh Jain
2023-02-23 20:34                 ` Eric DeVolder
2023-02-24  8:34                   ` Sourabh Jain
2023-02-24 20:16                     ` Eric DeVolder
2023-02-27  6:11                       ` Sourabh Jain
2023-02-28 21:50                         ` Eric DeVolder
2023-03-01  6:22                           ` Sourabh Jain
2023-03-01 14:16                             ` Eric DeVolder
2023-01-31 22:42 ` [PATCH v18 6/7] crash: memory and cpu hotplug sysfs attributes Eric DeVolder
2023-01-31 22:42 ` [PATCH v18 7/7] x86/crash: add x86 crash hotplug support Eric DeVolder

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