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From:   Aubrey Li <aubrey.intel@gmail.com>
Date:   Thu, 1 Aug 2019 15:16:40 +0800
Message-ID: <CAERHkruxfBc8DqNUr=fbYuQWrXrHC7cK6HnVR3xp0iLA9QtxiQ@mail.gmail.com>
Subject: Re: setup_boot_APIC_clock() NULL dereference during early boot on
 reduced hardware platforms
To:     Daniel Drake <drake@endlessm.com>
Cc:     Thomas Gleixner <tglx@linutronix.de>, x86@kernel.org,
        "Li, Aubrey" <aubrey.li@linux.intel.com>,
        Ingo Molnar <mingo@redhat.com>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Endless Linux Upstreaming Team <linux@endlessm.com>
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On Thu, Aug 1, 2019 at 2:26 PM Daniel Drake <drake@endlessm.com> wrote:
>
> Hi,
>
> Working with a new consumer laptop based on AMD R7-3700U, we are
> seeing a kernel panic during early boot (before the display
> initializes). It's a new product and there is no previous known
> working kernel version (tested 5.0, 5.2 and current linus master).
>
> We may have also seen this problem on a MiniPC based on AMD APU 7010
> from another vendor, but we don't have it in hands right now to
> confirm that it's the exact same crash.
>
> earlycon shows the details: a NULL dereference under
> setup_boot_APIC_clock(), which actually happens in
> calibrate_APIC_clock():
>
>     /* Replace the global interrupt handler */
>     real_handler = global_clock_event->event_handler;
>     global_clock_event->event_handler = lapic_cal_handler;
>
> global_clock_event is NULL here. This is a "reduced hardware" ACPI
> platform so acpi_generic_reduced_hw_init() has set timer_init to NULL,
> avoiding the usual codepaths that would set up global_clock_event.
>
IIRC, acpi_generic_reduced_hw_init() avoids initializing PIT, the status of
this legacy device is unknown in ACPI hw-reduced mode.

> I tried the obvious:
>  if (!global_clock_event)
>     return -1;
>
No, the platform needs a global clock event, can you turn on some other
clock source on your platform, like HPET?

Thanks,
-Aubrey

> However I'm probably missing part of the big picture here, as this
> only makes boot fail later on. It continues til the next point that
> something leads to schedule(), such as a driver calling msleep() or
> mark_readonly() calling rcu_barrier(), etc. Then it hangs.
>
> Is something missing in terms of timer setup here? Suggestions appreciated...
>
> Thanks
> Daniel