linux-kernel - Re: [PATCH v2 0/5] riscv: add PREEMPT

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Message-ID: <ea5cdba4-7a79-56b3-f8d7-7785569dedd6@microchip.com>
Date:   Fri, 2 Sep 2022 13:29:23 +0000
From:   <Conor.Dooley@...rochip.com>
To:     <jszhang@...nel.org>
CC:     <paul.walmsley@...ive.com>, <palmer@...belt.com>,
        <aou@...s.berkeley.edu>, <anup@...infault.org>,
        <atishp@...shpatra.org>, <bigeasy@...utronix.de>,
        <tglx@...utronix.de>, <rostedt@...dmis.org>,
        <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <kvm@...r.kernel.org>, <kvm-riscv@...ts.infradead.org>
Subject: Re: [PATCH v2 0/5] riscv: add PREEMPT_RT support

On 02/09/2022 14:09, Jisheng Zhang wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On Thu, Sep 01, 2022 at 04:41:52PM +0000, Conor.Dooley@...rochip.com wrote:
>> On 31/08/2022 18:59, Jisheng Zhang wrote:
>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>
>>> This series is to add PREEMPT_RT support to riscv:
>>> patch1 adds the missing number of signal exits in vCPU stat
>>> patch2 switches to the generic guest entry infrastructure
>>> patch3 select HAVE_POSIX_CPU_TIMERS_TASK_WORK which is a requirement for
>>> RT
>>> patch4 adds lazy preempt support
>>> patch5 allows to enable PREEMPT_RT
>>>
>>
>> What version of the preempt_rt patch did you test this with?
> 
> v6.0-rc1 + v6.0-rc1-rt patch
> 
>>
>> Maybe I am missing something, but I gave this a whirl with
>> v6.0-rc3 + v6.0-rc3-rt5 & was meant by a bunch of complaints.
>> I am not familiar with the preempt_rt patch, so I am not sure what
>> level of BUG()s or WARNING()s are to be expected, but I saw a fair
>> few...
> 
> Could you please provide corresponding log? Usually, this means there's
> a bug in related drivers, so it's better to fix them now rather than
> wait for RT patches mainlined.

I tried it on PolarFire SoC. I know that at least one of the problems
I found is down to drivers - specifically the system controller & hwrng.

The first issue that comes up is in early smp setup code - we call out
to update_siblings_masks() which does an alloc with preemption. It's
the same backtrace from here:

https://lore.kernel.org/all/0abd0acf-70a1-d546-a517-19efe60042d1@microchip.com/

I'll give it a run through tonight or tomorrow & give you a full log
of what I saw. There's some splats all over the place for me, but I
can't tell if that's just knock-on from the other issues.

Thanks,
Conor.