linux-kernel - Re: [PATCH v2] PCI: vmd: Create domain symlink before pci_bus_add

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Date: Tue, 4 Jun 2024 11:00:59 -0700
From: Paul M Stillwell Jr <paul.m.stillwell.jr@...el.com>
To: Jiwei Sun <sjiwei@....com>, <nirmal.patel@...ux.intel.com>,
	<jonathan.derrick@...ux.dev>
CC: <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 v2] PCI: vmd: Create domain symlink before
 pci_bus_add_devices()

On 6/4/2024 6:51 AM, 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
> 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().
> 
> Signed-off-by: Jiwei Sun <sunjw10@...ovo.com>
> Suggested-by: Adrian Huang <ahuang12@...ovo.com>
> ---
> v2 changes:
>   - Add "()" after function names in subject and commit log
>   - Move sysfs_create_link() after vmd_attach_resources()
> 
> ---
>   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..d0e33e798bb9 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -925,6 +925,9 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
>   		dev_set_msi_domain(&vmd->bus->dev,
>   				   dev_get_msi_domain(&vmd->dev->dev));
>   
> +	WARN(sysfs_create_link(&vmd->dev->dev.kobj, &vmd->bus->dev.kobj,
> +			       "domain"), "Can't create symlink to domain\n");
> +

I think you should move the sysfs_remove_link() line in vmd_remove() 
down as well.

Paul

>   	vmd_acpi_begin();
>   
>   	pci_scan_child_bus(vmd->bus);
> @@ -964,9 +967,6 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
>   	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;
>   }
>