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Date: Sun, 12 Jul 2026 16:28:18 +0200
From: Lukas Wunner <lukas@wunner.de>
To: Maurice Hieronymus <mhi@mailbox.org>
Cc: Edward Cree <ecree.xilinx@gmail.com>,
	Andrew Lunn <andrew+netdev@lunn.ch>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Justin Tee <justin.tee@broadcom.com>,
	Paul Ely <paul.ely@broadcom.com>,
	"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	Juergen Gross <jgross@suse.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
	Miguel Ojeda <ojeda@kernel.org>, Boqun Feng <boqun@kernel.org>,
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	=?iso-8859-1?Q?Bj=F6rn?= Roy Baron <bjorn3_gh@protonmail.com>,
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	Onur =?iso-8859-1?Q?=D6zkan?= <work@onurozkan.dev>,
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	netdev@vger.kernel.org, linux-net-drivers@amd.com,
	linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-scsi@vger.kernel.org, xen-devel@lists.xenproject.org,
	linux-edac@vger.kernel.org
Subject: Re: [PATCH 1/2] PCI: Replace pci_dev->is_busmaster with accessors
Message-ID: <alOkgrK7Fm6opB4r@wunner.de>
References: <20260711-pci-dev-flags-v1-0-2fcf2811138c@mailbox.org>
 <20260711-pci-dev-flags-v1-1-2fcf2811138c@mailbox.org>
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In-Reply-To: <20260711-pci-dev-flags-v1-1-2fcf2811138c@mailbox.org>

On Sat, Jul 11, 2026 at 05:21:06PM +0200, Maurice Hieronymus wrote:
> `is_busmaster` is one bit of a ~60-bit C bitfield in `struct pci_dev`.
> Bits sharing a bitfield word must not be modified concurrently, but its
> writers take no common lock: `pci_set_master()` can run without the
> device lock (e.g. from runtime PM resume paths), `pci_disable_device()`
> clears the bit, and other bits in the same word are written from
> entirely different contexts, e.g. `broken_parity_status` from sysfs.
> Concurrent read-modify-write cycles of the shared word can then lose
> updates.
> 
> Move `is_busmaster` into a new `flags` bitmap modified with atomic
> bitops and accessed through generated accessor functions, following the
> example of commit a7cc262a1135 ("driver core: Replace dev->offline +
> ->offline_disabled with accessors"). More bitfield flags can follow the
> same pattern later.

We already have the priv_flags member in struct pci_dev,
please use that instead of adding another one for the same purpose.

Thanks,

Lukas