linux-kernel - Re: [PATCH] PCI: vmd: Create domain symlink before pci_bus_add

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Date: Mon, 3 Jun 2024 15:55:11 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Jiwei Sun <sjiwei@....com>
Cc: nirmal.patel@...ux.intel.com, jonathan.derrick@...ux.dev,
	lpieralisi@...nel.org, kw@...ux.com, robh@...nel.org,
	bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, sunjw10@...ovo.com,
	ahuang12@...ovo.com
Subject: Re: [PATCH] PCI: vmd: Create domain symlink before
 pci_bus_add_devices

On Mon, Jun 03, 2024 at 10:03:29PM +0800, Jiwei Sun wrote:
> From: Jiwei Sun <sunjw10@...ovo.com>
> 
> During booting into the kernel, the following error message appears:
> 
>   (udev-worker)[2149]: nvme1n1: '/sbin/mdadm -I /dev/nvme1n1'(err) 'mdadm: Unable to get real path for '/sys/bus/pci/drivers/vmd/0000:c7:00.5/domain/device''
>   (udev-worker)[2149]: nvme1n1: '/sbin/mdadm -I /dev/nvme1n1'(err) 'mdadm: /dev/nvme1n1 is not attached to Intel(R) RAID controller.'
>   (udev-worker)[2149]: nvme1n1: '/sbin/mdadm -I /dev/nvme1n1'(err) 'mdadm: No OROM/EFI properties for /dev/nvme1n1'
>   (udev-worker)[2149]: nvme1n1: '/sbin/mdadm -I /dev/nvme1n1'(err) 'mdadm: no RAID superblock on /dev/nvme1n1.'
>   (udev-worker)[2149]: nvme1n1: Process '/sbin/mdadm -I /dev/nvme1n1' failed with exit code 1.
> 
> This symptom prevents the OS from booting successfully.
> 
> After a NVMe disk is probed/added by the nvme driver, the udevd executes
> some rule scripts by invoking mdadm command to detect if there is a
> mdraid associated with this NVMe disk. The mdadm determines if one
> NVMe devce is connected to a particular VMD domain by checking the
       device

> domain symlink. Here is the root cause:
> 
> Thread A                   Thread B             Thread mdadm
> vmd_enable_domain
>   pci_bus_add_devices
>     __driver_probe_device
>      ...
>      work_on_cpu
>        schedule_work_on
>        : wakeup Thread B
>                            nvme_probe
>                            : wakeup scan_work
>                              to scan nvme disk
>                              and add nvme disk
>                              then wakeup udevd
>                                                 : udevd executes
>                                                   mdadm command
>        flush_work                               main
>        : wait for nvme_probe done                ...
>     __driver_probe_device                        find_driver_devices
>     : probe next nvme device                     : 1) Detect the domain
>     ...                                            symlink; 2) Find the
>     ...                                            domain symlink from
>     ...                                            vmd sysfs; 3) The
>     ...                                            domain symlink is not
>     ...                                            created yet, failed
>   sysfs_create_link
>   : create domain symlink
> 
> sysfs_create_link is invoked at the end of vmd_enable_domain. However,
> this implementation introduces a timing issue, where mdadm might fail
> to retrieve the vmd symlink path because the symlink has not been
> created yet.
> 
> Fix the issue by creating VMD domain symlinks before invoking
> pci_bus_add_devices.

Add "()" after function names in subject and commit log.

> Signed-off-by: Jiwei Sun <sunjw10@...ovo.com>
> Suggested-by: Adrian Huang <ahuang12@...ovo.com>
> ---
>  drivers/pci/controller/vmd.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index 87b7856f375a..3f208c5f9ec9 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -961,12 +961,12 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
>  	list_for_each_entry(child, &vmd->bus->children, node)
>  		pcie_bus_configure_settings(child);
>  
> +	WARN(sysfs_create_link(&vmd->dev->dev.kobj, &vmd->bus->dev.kobj,
> +			       "domain"), "Can't create symlink to domain\n");

Seems OK to me.  IIUC, this "domain" link is created in the directory
of the VMD pci_dev, and it points to the directory of the new "root
bus" behind the VMD.

Since it's unrelated to the *devices* on that new root bus, I would
probably move this even earlier, so it's with the other code that sets
up the new root bus, e.g., somewhere around vmd_attach_resources().

>  	pci_bus_add_devices(vmd->bus);
>  
>  	vmd_acpi_end();
> -
> -	WARN(sysfs_create_link(&vmd->dev->dev.kobj, &vmd->bus->dev.kobj,
> -			       "domain"), "Can't create symlink to domain\n");
>  	return 0;
>  }
>  
> -- 
> 2.27.0
>