linux-kernel - Re: [PATCH v5 00/13] riscv: improve boot time isa extensions handling

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Message-ID: <48d2ac96-abdd-23bc-b167-08dc2c1a1dbe@roeck-us.net>
Date:   Sun, 12 Feb 2023 10:38:26 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Conor Dooley <conor@...nel.org>
Cc:     Jisheng Zhang <jszhang@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup@...infault.org>,
        Atish Patra <atishp@...shpatra.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Andrew Jones <ajones@...tanamicro.com>,
        Conor Dooley <conor.dooley@...rochip.com>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org
Subject: Re: [PATCH v5 00/13] riscv: improve boot time isa extensions handling

On 2/12/23 10:20, Conor Dooley wrote:
> On Sun, Feb 12, 2023 at 10:14:13AM -0800, Guenter Roeck wrote:
>> On 2/12/23 10:06, Conor Dooley wrote:
>>> On Sun, Feb 12, 2023 at 05:06:09PM +0000, Conor Dooley wrote:
>>>> On Sun, Feb 12, 2023 at 04:33:58PM +0000, Conor Dooley wrote:
>>>>> On Sun, Feb 12, 2023 at 03:59:59PM +0000, Conor Dooley wrote:
>>>>
>>>> So as not to lead anyone up the garden path, let me correct myself:
>>>>
>>>>> Hmm, so this appears to be us attempting to patch in alternatives where
>>>>> none actually exists - seemingly F & D.
>>>>
>>>> And of course that's not true, riscv_has_extension_likely() now uses
>>>> alternatives as of:
>>>> bdda5d554e43 ("riscv: introduce riscv_has_extension_[un]likely()")
>>>>
>>>>   From a quick look, it just happens that the only users are F & D.
>>>>
>>>
>>> Samuel pointed out that this is a lockdep splat on irc.
>>> There's a patch on the list that removes the lockdep annotation
>>> entirely:
>>> https://patchwork.kernel.org/project/linux-riscv/patch/20230202114116.3695793-1-changbin.du@huawei.com/
>>>
>>> So ye, no surprises that it was config based!
>>>
>>> Palmer posted a "better" fix for that lockdep warning a while ago:
>>> https://lore.kernel.org/all/20220322022331.32136-1-palmer@rivosinc.com/
>>>
>>> So we'd have to duplicate/reuse that for cpufeature/errata patching.
>>>
>>>
>>
>> This does not (only) happen in stop_machine().
> 
> Yah, sorry I meant that it's the same lockdep splat as is being
> addressed there.
> The first patch deletes the lockdep stuff entirely, so removes the
> splat. I was thinking that we'd need to take Palmer's (IMO better)
> patch and do the same thing for patching alternatives, but I figure we
> can just take the text_mutex itself for alternatives & not have to
> dance around the lock.
> 
> I'll go do that I suppose!

Thanks a lot for the clarification. That sounds like the backtrace
can be largely ignored. However, I still see that the patch series
results in boot hangs with the sifive_u qemu emulation, where
the log ends with "Oops - illegal instruction". Is that problem
being addressed as well ?

Thanks,
Guenter