linux-kernel - Re: [PATCH v2] PCI: vmd: Fix spinlock usage on config access for RT kernel

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Message-Id: <20241219005336.8603-1-ryotkkr98@gmail.com>
Date: Thu, 19 Dec 2024 09:53:36 +0900
From: Ryo Takakura <ryotkkr98@...il.com>
To: lgoncalv@...hat.com,
	bigeasy@...utronix.de,
	kbusch@...nel.org
Cc: bhelgaas@...gle.com,
	jonathan.derrick@...ux.dev,
	kw@...ux.com,
	linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org,
	linux-rt-devel@...ts.linux.dev,
	lpieralisi@...nel.org,
	manivannan.sadhasivam@...aro.org,
	nirmal.patel@...ux.intel.com,
	robh@...nel.org,
	rostedt@...dmis.org
Subject: Re: [PATCH v2] PCI: vmd: Fix spinlock usage on config access for RT kernel

Hi all!

on Wed, 18 Dec 2024 13:35:07 -0300, Luis Claudio R. Goncalves wrote:
>On Wed, Dec 18, 2024 at 08:57:53AM -0700, Keith Busch wrote:
>> On Wed, Dec 18, 2024 at 04:48:38PM +0100, Sebastian Andrzej Siewior wrote:
>> > 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?
>> 
>> The arch/x86/Kconfig always selects PCI_LOCKESS_CONFIG, so I don't think
>> the vmd driver can require it be turned off. Besides, no need to punish
>> all PCI access if only this device requires it be serialized.
>
>Sorry, I also missed that and induced Ryo Takakura to rewrite the patch.

My apologies I missed that as well.
I'll send the first version of the patch once again!

>Luis

Sincerely,
Ryo Takakura