From:   Alexander Stein <alexander.stein@ew.tq-group.com>
To:     Bjorn Helgaas <bhelgaas@google.com>
Cc:     Korneliusz Osmenda <korneliuszo@gmail.com>,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 1/1] Guard pci_create_sysfs_dev_files with atomic value
Date:   Thu, 16 Mar 2023 10:18:22 +0100
Message-ID: <4335627.mvXUDI8C0e@steina-w>
Organization: TQ-Systems GmbH
In-Reply-To: <20230316091540.494366-1-alexander.stein@ew.tq-group.com>
References: <20230316091540.494366-1-alexander.stein@ew.tq-group.com>
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Hi,

for some reason my additional info was missing. See below.

Am Donnerstag, 16. M=E4rz 2023, 10:15:40 CET schrieb Alexander Stein:
> From: Korneliusz Osmenda <korneliuszo@gmail.com>
>=20
> On Gateworks Ventana there is a number of PCI devices and:
>   - imx6_pcie_probe takes longer than start of late init
>   - pci_sysfs_init sets up flag sysfs_initialized
>   - pci_sysfs_init initializes already found devices
>   - imx6_pcie_probe tries to reinitialize device
>=20
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=3D215515
>=20
> Signed-off-by: Korneliusz Osmenda <korneliuszo@gmail.com>
> Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
> ---

Changes in v2:
* Rebased to next-20230323
* checkpath.pl fixes

I'm hitting the same issue on TQMa6x+MBa6x. There is a race in
pci_sysfs_init late initcall and pci_bus_add_device due to regular PCIe
bus probing. Having some debug output 'sysfs_initialized' is set to 1
while pci_bus_add_devices is still adding PCIe devices.
Having this patch applied my PCIe device using several bridges is detected
fine.

My PCIe bus looks like thi (using this patch):
root@tqma6-common:~# lspci
00:00.0 PCI bridge: Synopsys, Inc. DWC_usb3 / PCIe bridge (rev 01)
01:00.0 PCI bridge: Pericom Semiconductor Device a303 (rev 03)
02:01.0 PCI bridge: Pericom Semiconductor Device a303 (rev 03)
02:02.0 PCI bridge: Pericom Semiconductor Device a303 (rev 03)
03:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8=
411
PCI Express Gigabit Ethernet Controller (rev 0c)
04:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8=
411
PCI Express Gigabit Ethernet Controller (rev 0c)

root@tqma6-common:~# lspci -t
=2D[0000:00]---00.0-[01-ff]----00.0-[02-04]--+-01.0-[03]----00.0
                                           \-02.0-[04]----00.0

Best regards,
Alexander

>  drivers/pci/pci-sysfs.c | 6 ++++++
>  include/linux/pci.h     | 2 ++
>  2 files changed, 8 insertions(+)
>=20
> diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c
> index dd0d9d9bc509..998e44716b6f 100644
> --- a/drivers/pci/pci-sysfs.c
> +++ b/drivers/pci/pci-sysfs.c
> @@ -1497,6 +1497,9 @@ int __must_check pci_create_sysfs_dev_files(struct
> pci_dev *pdev) if (!sysfs_initialized)
>  		return -EACCES;
>=20
> +	if (atomic_cmpxchg(&pdev->sysfs_init_cnt, 0, 1) =3D=3D 1)
> +		return 0;		/* already added */
> +
>  	return pci_create_resource_files(pdev);
>  }
>=20
> @@ -1511,6 +1514,9 @@ void pci_remove_sysfs_dev_files(struct pci_dev *pde=
v)
>  	if (!sysfs_initialized)
>  		return;
>=20
> +	if (atomic_cmpxchg(&pdev->sysfs_init_cnt, 1, 0) =3D=3D 0)
> +		return;		/* already removed */
> +
>  	pci_remove_resource_files(pdev);
>  }
>=20
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index b50e5c79f7e3..024313a7a90a 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -467,6 +467,8 @@ struct pci_dev {
>  	pci_dev_flags_t dev_flags;
>  	atomic_t	enable_cnt;	/* pci_enable_device has been called=20
*/
>=20
> +	atomic_t	sysfs_init_cnt;	/* pci_create_sysfs_dev_files has been=20
called */
> +
>  	u32		saved_config_space[16]; /* Config space saved at=20
suspend time */
>  	struct hlist_head saved_cap_space;
>  	int		rom_attr_enabled;	/* Display of ROM attribute=20
enabled? */


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