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Subject: Re: [PATCH 1/1] arm64: kexec: machine_kexec should call
 __flush_icache_range
To:     AKASHI Takahiro <takahiro.akashi@linaro.org>,
        Will Deacon <will.deacon@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org
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 <d9bac115-794c-4225-bcaa-91b6847604a2@oracle.com>
 <20180731002830.GJ11258@linaro.org>
From:   Dave Kleikamp <dave.kleikamp@oracle.com>
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Date:   Mon, 30 Jul 2018 19:31:16 -0500
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On 07/30/2018 07:28 PM, AKASHI Takahiro wrote:
> On Mon, Jul 30, 2018 at 04:36:28PM -0500, Dave Kleikamp wrote:
>> On 07/30/2018 11:57 AM, Will Deacon wrote:
>>> On Mon, Jul 30, 2018 at 11:46:24AM -0500, Dave Kleikamp wrote:
>>>> On 07/30/2018 11:22 AM, Will Deacon wrote:
>>>>> On Mon, Jul 30, 2018 at 05:16:42PM +0100, Catalin Marinas wrote:
>>>>>> On Mon, Jul 30, 2018 at 10:29:21AM -0500, Dave Kleikamp wrote:
>>>>>>> machine_kexec flushes the reboot_code_buffer from the icache
>>>>>>> after stopping the other cpus.
>>>>>>>
>>>>>>> Commit 3b8c9f1cdfc5 ("arm64: IPI each CPU after invalidating the I-cache
>>>>>>> for kernel mappings") added an IPI call to flush_icache_range, which
>>>>>>> causes a hang here, so replace the call with __flush_icache_range
>>>>>>
>>>>>> While machine_kexec() may be called with interrupts disabled (IIUC) and
>>>>>> we shouldn't IPI other CPUs, I don't understand why it hangs here. Are
>>>>>> there any other CPUs online at this point?
>>>>>
>>>>> The BUG_ON and WARN_ON at the start of machine_kexec() suggest to me that
>>>>> this should only happen if we're kexec'ing a crash kernel and
>>>>> smp_crash_stop_failed(). Is that something we need to care about?
>>>>
>>>> I observed the hang trying to kexec a crash kernel and I did not see the
>>>> warning that smp_crash_stop_failed(). I'm not exactly sure why
>>>> flush_icache_range() hung (but it did), but I think that
>>>> __flush_icache_range() makes more sense here anyway.
>>>
>>> Yeah, I'll pick the patch up, but it would be nice to understand the
>>> failure case you observed.
>>
>> I see why it failed. ipi_cpu_crash_stop() does not call
>> set_cpu_online(cpu, false) the way ipi_cpu_stop() does. So
>> cpu_online_mask is still populated with the stopped cpus.
>>
>> Any reason why it isn't called there?
> 
> Because I wanted that saved cpu-related state be as close to as it was
> at panic.
> If cpus go offline, the core dump would show that all the cores but
> a panicked one be offline whether or not they actually were.

That makes sense.

Thanks,
Dave

> 
> Thanks,
> -Takahiro AKASHI
> 
>> Thanks,
>> Dave
>>
>>>
>>> Will
>>>