linux-kernel - Re: [PATCH v6 13/13] riscv: Add qspinlock support

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Message-ID: <20241128134135.GA3460@willie-the-truck>
Date: Thu, 28 Nov 2024 13:41:36 +0000
From: Will Deacon <will@...nel.org>
To: Conor Dooley <conor.dooley@...rochip.com>
Cc: Alexandre Ghiti <alexghiti@...osinc.com>,
	Jonathan Corbet <corbet@....net>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Conor Dooley <conor@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Andrea Parri <parri.andrea@...il.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, Waiman Long <longman@...hat.com>,
	Boqun Feng <boqun.feng@...il.com>, Arnd Bergmann <arnd@...db.de>,
	Leonardo Bras <leobras@...hat.com>, Guo Ren <guoren@...nel.org>,
	linux-doc@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH v6 13/13] riscv: Add qspinlock support

On Thu, Nov 28, 2024 at 12:56:55PM +0000, Conor Dooley wrote:
> On Sun, Nov 03, 2024 at 03:51:53PM +0100, Alexandre Ghiti wrote:
> > In order to produce a generic kernel, a user can select
> > CONFIG_COMBO_SPINLOCKS which will fallback at runtime to the ticket
> > spinlock implementation if Zabha or Ziccrse are not present.
> > 
> > Note that we can't use alternatives here because the discovery of
> > extensions is done too late and we need to start with the qspinlock
> > implementation because the ticket spinlock implementation would pollute
> > the spinlock value, so let's use static keys.
> > 
> > This is largely based on Guo's work and Leonardo reviews at [1].
> > 
> > Link: https://lore.kernel.org/linux-riscv/20231225125847.2778638-1-guoren@kernel.org/ [1]
> > Signed-off-by: Guo Ren <guoren@...nel.org>
> > Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
> 
> This patch (now commit ab83647fadae2 ("riscv: Add qspinlock support"))
> breaks boot on polarfire soc. It dies before outputting anything to the
> console. My .config has:
> 
> # CONFIG_RISCV_TICKET_SPINLOCKS is not set
> # CONFIG_RISCV_QUEUED_SPINLOCKS is not set
> CONFIG_RISCV_COMBO_SPINLOCKS=y

I pointed out some of the fragility during review:

https://lore.kernel.org/all/20241111164259.GA20042@willie-the-truck/

so I'm kinda surprised it got merged tbh :/

Will