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

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Date: Wed, 5 Jun 2024 16:04:18 +0800
From: Jiwei Sun <sjiwei@....com>
To: Paul M Stillwell Jr <paul.m.stillwell.jr@...el.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 6/5/24 02:00, Paul M Stillwell Jr wrote:
> 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.

Indeed, thanks for your suggestion. I will modify it in v3 patch.

Thanks,
Regards,
Jiwei

> 
> 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;
>>   }
>>