linux-kernel - Re: [PATCH 1/1] arm64: kexec: machine_kexec should call __flush_icache

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Message-ID: <d9bac115-794c-4225-bcaa-91b6847604a2@oracle.com>
Date:   Mon, 30 Jul 2018 16:36:28 -0500
From:   Dave Kleikamp <dave.kleikamp@...cle.com>
To:     Will Deacon <will.deacon@....com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/1] arm64: kexec: machine_kexec should call
 __flush_icache_range

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?

Thanks,
Dave

> 
> Will
>