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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Keith Busch <kbusch@kernel.org>
Cc: Ryo Takakura <ryotkkr98@gmail.com>, lgoncalv@redhat.com,
	bhelgaas@google.com, jonathan.derrick@linux.dev, kw@linux.com,
	lpieralisi@kernel.org, manivannan.sadhasivam@linaro.org,
	nirmal.patel@linux.intel.com, robh@kernel.org, rostedt@goodmis.org,
	linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-rt-devel@lists.linux.dev
Subject: Re: [PATCH v2] PCI: vmd: Fix spinlock usage on config access for RT
 kernel
Message-ID: <20241218154838.xVrjbjeX@linutronix.de>
References: <20241218115951.83062-1-ryotkkr98@gmail.com>
 <Z2LsFoXotl_SHmNk@kbusch-mbp.dhcp.thefacebook.com>
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In-Reply-To: <Z2LsFoXotl_SHmNk@kbusch-mbp.dhcp.thefacebook.com>

On 2024-12-18 08:36:54 [-0700], Keith Busch wrote:
> On Wed, Dec 18, 2024 at 08:59:51PM +0900, Ryo Takakura wrote:
> > PCI config access is locked with pci_lock which serializes
> > pci_user/bus_write_config*() and pci_user/bus_read_config*().
> > The subsequently invoked vmd_pci_write() and vmd_pci_read() are also
> > serialized as they are only invoked by them respectively.
> > 
> > Remove cfg_lock which is taken by vmd_pci_write() and vmd_pci_read()
> > for their serialization as its already serialized by pci_lock.
> 
> That's only true if CONFIG_PCI_LOCKLESS_CONFIG isn't set, so pci_lock
> won't help with concurrent kernel config access in such a setup. I think
> the previous change to raw lock proposal was the correct approach.

I overlooked that. Wouldn't it make sense to let the vmd driver select
that option rather than adding/ having a lock for the same purpose?

Sebastian