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From: Stephen Warren <swarren@wwwdotorg.org>
To: Vijay Kilari <vijay.kilari@gmail.com>
Cc: "linux@arm.linux.org.uk" <linux@arm.linux.org.uk>,
	Prasun.Kapoor@caviumnetworks.com,
	Will Deacon <will.deacon@arm.com>,
	Vijaya Kumar K <Vijaya.Kumar@caviumnetworks.com>,
	kexec@lists.infradead.org,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] ARM: kexec: offline non panic CPUs on Kdump panic
Date: Tue, 30 Jul 2013 10:57:12 -0600	[thread overview]
Message-ID: <51F7F068.8060509@wwwdotorg.org> (raw)
In-Reply-To: <CALicx6s5NX9ZaEiiGo1A=jT+o7Lpj8Y4ubkHeeK2p3DmZpwQeg@mail.gmail.com>

On 07/30/2013 04:05 AM, Vijay Kilari wrote:
> On Fri, Jul 26, 2013 at 10:35 PM, Stephen Warren <swarren@wwwdotorg.org> wrote:
>> On 07/25/2013 11:41 PM, vijay.kilari@gmail.com wrote:
>>> From: Vijaya Kumar K <Vijaya.Kumar@caviumnetworks.com>
>>>
>>> In case of normal kexec kernel load, all cpu's are offlined
>>> before calling machine_kexec() under kernel_kexec() function.
>>
>> I'm not sure that's true, unless perhaps you have CONFIG_KEXEC_JUMP enabled?
>>
>>> But in case crash panic cpus are relaxed in
>>> machine_crash_nonpanic_core() SMP function but not offlined.
>>>
>>> When crash kernel is loaded with kexec and on panic trigger
>>> machine_kexec() checks for number of cpus online.
>>> If more than one cpu is online machine_kexec() fails to load
>>> with below error
>>>
>>> kexec: error: multiple CPUs still online
>>>
>>> In machine_crash_nonpanic_core() SMP function, offline CPU
>>> before cpu_relax
>>
>>> diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
>>
>>> @@ -73,6 +73,7 @@ void machine_crash_nonpanic_core(void *unused)
>>>       crash_save_cpu(&regs, smp_processor_id());
>>>       flush_cache_all();
>>>
>>> +     set_cpu_online(smp_processor_id(), false);
>>
>> I'm not familiar with that API, but it looks like it's just setting the
>> *current* CPU offline. That sounds problematic for two reasons:
>>
>> 1) Setting the current CPU offline sounds like a bad idea; after all,
>> code is still running on it. Presumably you want to offline all other CPUs.
>>
>    machine_crash_nonpanic_core() is a SMP call (smp_call_function) .
>    Setting cpu offline is called for all other CPUs except the caller.

Ah OK, that's what I was missing. This makes sense then.

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WARNING: multiple messages have this Message-ID (diff)
From: swarren@wwwdotorg.org (Stephen Warren)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] ARM: kexec: offline non panic CPUs on Kdump panic
Date: Tue, 30 Jul 2013 10:57:12 -0600	[thread overview]
Message-ID: <51F7F068.8060509@wwwdotorg.org> (raw)
In-Reply-To: <CALicx6s5NX9ZaEiiGo1A=jT+o7Lpj8Y4ubkHeeK2p3DmZpwQeg@mail.gmail.com>

On 07/30/2013 04:05 AM, Vijay Kilari wrote:
> On Fri, Jul 26, 2013 at 10:35 PM, Stephen Warren <swarren@wwwdotorg.org> wrote:
>> On 07/25/2013 11:41 PM, vijay.kilari at gmail.com wrote:
>>> From: Vijaya Kumar K <Vijaya.Kumar@caviumnetworks.com>
>>>
>>> In case of normal kexec kernel load, all cpu's are offlined
>>> before calling machine_kexec() under kernel_kexec() function.
>>
>> I'm not sure that's true, unless perhaps you have CONFIG_KEXEC_JUMP enabled?
>>
>>> But in case crash panic cpus are relaxed in
>>> machine_crash_nonpanic_core() SMP function but not offlined.
>>>
>>> When crash kernel is loaded with kexec and on panic trigger
>>> machine_kexec() checks for number of cpus online.
>>> If more than one cpu is online machine_kexec() fails to load
>>> with below error
>>>
>>> kexec: error: multiple CPUs still online
>>>
>>> In machine_crash_nonpanic_core() SMP function, offline CPU
>>> before cpu_relax
>>
>>> diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
>>
>>> @@ -73,6 +73,7 @@ void machine_crash_nonpanic_core(void *unused)
>>>       crash_save_cpu(&regs, smp_processor_id());
>>>       flush_cache_all();
>>>
>>> +     set_cpu_online(smp_processor_id(), false);
>>
>> I'm not familiar with that API, but it looks like it's just setting the
>> *current* CPU offline. That sounds problematic for two reasons:
>>
>> 1) Setting the current CPU offline sounds like a bad idea; after all,
>> code is still running on it. Presumably you want to offline all other CPUs.
>>
>    machine_crash_nonpanic_core() is a SMP call (smp_call_function) .
>    Setting cpu offline is called for all other CPUs except the caller.

Ah OK, that's what I was missing. This makes sense then.

  reply	other threads:[~2013-07-30 16:57 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-07-26  5:41 [PATCH] ARM: kexec: offline non panic CPUs on Kdump panic vijay.kilari
2013-07-26  5:41 ` vijay.kilari at gmail.com
2013-07-26 10:49 ` Will Deacon
2013-07-26 10:49   ` Will Deacon
2013-07-26 17:08   ` Stephen Warren
2013-07-26 17:08     ` Stephen Warren
2013-07-26 17:11     ` Will Deacon
2013-07-26 17:11       ` Will Deacon
2013-07-30 10:37     ` Vijay Kilari
2013-07-30 10:37       ` Vijay Kilari
2013-07-30 16:59       ` Stephen Warren
2013-07-30 16:59         ` Stephen Warren
2013-07-31 11:37         ` Vijay Kilari
2013-07-31 11:37           ` Vijay Kilari
2013-07-31 17:14           ` Stephen Warren
2013-07-31 17:14             ` Stephen Warren
2013-08-01 13:49             ` Vijay Kilari
2013-08-01 13:49               ` Vijay Kilari
2013-08-01 16:25               ` Stephen Warren
2013-08-01 16:25                 ` Stephen Warren
2013-08-12 12:18                 ` Vijay Kilari
2013-08-12 12:18                   ` Vijay Kilari
2013-08-13 11:18                   ` Will Deacon
2013-08-13 11:18                     ` Will Deacon
2013-07-26 17:05 ` Stephen Warren
2013-07-26 17:05   ` Stephen Warren
2013-07-30 10:05   ` Vijay Kilari
2013-07-30 10:05     ` Vijay Kilari
2013-07-30 16:57     ` Stephen Warren [this message]
2013-07-30 16:57       ` Stephen Warren

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