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

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Date:   Mon, 30 Jul 2018 17:57:57 +0100
From:   Will Deacon <will.deacon@....com>
To:     Dave Kleikamp <dave.kleikamp@...cle.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 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.

Will