From: Christophe Leroy <christophe.leroy@c-s.fr>
To: Chris Packham <Chris.Packham@alliedtelesis.co.nz>,
"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
"mpe@ellerman.id.au" <mpe@ellerman.id.au>,
"npiggin@gmail.com" <npiggin@gmail.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Grant McEwan <grant.mcewan@alliedtelesis.co.nz>
Subject: Re: SMP lockup at boot on Freescale/NXP T2080 (powerpc 64)
Date: Thu, 8 Aug 2019 15:12:03 +0200 [thread overview]
Message-ID: <dcdaadb0-209c-605b-f117-fb6d872e2cd8@c-s.fr> (raw)
In-Reply-To: <b0ad453c-3a2b-6dd5-7bfc-5e275aa7bf62@c-s.fr>
Le 08/08/2019 à 10:46, Christophe Leroy a écrit :
>
>
> Le 07/08/2019 à 03:24, Chris Packham a écrit :
>> On Wed, 2019-08-07 at 11:13 +1000, Michael Ellerman wrote:
>>> Chris Packham <Chris.Packham@alliedtelesis.co.nz> writes:
>>>>
>>>> On Tue, 2019-08-06 at 21:32 +1000, Michael Ellerman wrote:
>>>> The difference between a working and non working defconfig is
>>>> CONFIG_PREEMPT specifically CONFIG_PREEMPT=y makes my system hang
>>>> at
>>>> boot.
>>>>
>>>> Is that now intentionally prohibited on 64-bit powerpc?
>>> It's not prohibitied, but it probably should be because no one really
>>> tests it properly. I have a handful of IBM machines where I boot a
>>> PREEMPT kernel but that's about it.
>>>
>>> The corenet configs don't have PREEMPT enabled, which suggests it was
>>> never really supported on those machines.
>>>
>>> But maybe someone from NXP can tell me otherwise.
>>>
>>
>> I think our workloads need CONFIG_PREEMPT=y because our systems have
>> switch ASIC drivers implemented in userland and we need to be able to
>> react quickly to network events in order to prevent loops. We have seen
>> instances of this not happening simply because some other process is in
>> the middle of a syscall.
>>
>> One thing I am working on here is a setup with a few vendor boards and
>> some of our own kit that we can test the upstream kernels on. Hopefully
>> that'd make these kinds of reports more timely rather than just
>> whenever we decide to move to a new kernel version.
>>
>>
>
>
> The defconfig also sets CONFIG_DEBUG_PREEMPT. Have you tried without
> CONFIG_DEBUG_PREEMPT ?
>
Reproduced on QEMU. CONFIG_DEBUG_PREEMPT is the trigger. Due to
smp_processor_id() being called from early_init_this_mmu(), when
CONFIG_DEBUG_PREEMPT is set debug_smp_processor_id() is called instead
of raw_smp_processor_id(), but this is too early for
debug_smp_processor_id()
As this call is useless, just drop it.
Can you test patch at https://patchwork.ozlabs.org/patch/1144005/ ?
Thanks
Christophe
prev parent reply other threads:[~2019-08-08 13:15 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-05 2:06 SMP lockup at boot on Freescale/NXP T2080 (powerpc 64) Chris Packham
2019-08-05 8:47 ` Chris Packham
2019-08-06 11:32 ` Michael Ellerman
2019-08-06 23:50 ` Chris Packham
2019-08-07 1:13 ` Michael Ellerman
2019-08-07 1:24 ` Chris Packham
2019-08-08 8:46 ` Christophe Leroy
2019-08-08 13:12 ` Christophe Leroy [this message]
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