Re: [PATCH 2/2] nvme: add 'queue_if_no_path' semantics

[Hannes Reinecke <hare@suse.de>]

On 10/6/20 3:30 PM, Hannes Reinecke wrote:
> On 10/6/20 10:39 AM, Christoph Hellwig wrote:
>> On Tue, Oct 06, 2020 at 10:29:49AM +0200, Hannes Reinecke wrote:
>>>> All multipath devices should behave the same.  No special casing for
>>>> PCIe, please.
>>>>
>>> Even if the default behaviour breaks PCI hotplug?
>>
>> Why would it "break" PCI hotplug?
>>
> When running under MD RAID:
> Before hotplug:
> # nvme list
> Node             SN                   Model       Namespace 
> Usage                      Format           FW Rev
> ---------------- -------------------- 
> ---------------------------------------- --------- 
> -------------------------- ---------------- --------
> /dev/nvme0n1     SLESNVME1            QEMU NVMe Ctrl       1          
> 17.18  GB /  17.18  GB    512   B +  0 B   1.0
> /dev/nvme1n1     SLESNVME2            QEMU NVMe Ctrl       1           
> 4.29  GB /   4.29  GB    512   B +  0 B   1.0
> /dev/nvme2n1     SLESNVME3            QEMU NVMe Ctrl       1           
> 4.29  GB /   4.29  GB    512   B +  0 B   1.0
> After hotplug:
> 
> # nvme list
> Node             SN                   Model       Namespace 
> Usage                      Format           FW Rev
> ---------------- -------------------- 
> ---------------------------------------- --------- 
> -------------------------- ---------------- --------
> /dev/nvme0n1     SLESNVME1            QEMU NVMe Ctrl       1          
> 17.18  GB /  17.18  GB    512   B +  0 B   1.0
> /dev/nvme1n1     SLESNVME2            QEMU NVMe Ctrl       -1          
> 0.00   B /   0.00   B      1   B +  0 B   1.0
> /dev/nvme1n2     SLESNVME2            QEMU NVMe Ctrl       1           
> 4.29  GB /   4.29  GB    512   B +  0 B   1.0
> /dev/nvme2n1     SLESNVME3            QEMU NVMe Ctrl       1           
> 4.29  GB /   4.29  GB    512   B +  0 B   1.0
> 
> And MD hasn't been notified that the device is gone:
> # cat /proc/mdstat
> Personalities : [raid10]
> md0 : active raid10 nvme2n1[1] nvme1n1[0]
>        4189184 blocks super 1.2 2 near-copies [2/2] [UU]
>        bitmap: 0/1 pages [0KB], 65536KB chunk
> 
> unused devices: <none>
> 
> Once I do some I/O to it MD recognized a faulty device:
> 
> # cat /proc/mdstat
> Personalities : [raid10]
> md0 : active raid10 nvme2n1[1] nvme1n1[0](F)
>        4189184 blocks super 1.2 2 near-copies [2/1] [_U]
>        bitmap: 0/1 pages [0KB], 65536KB chunk
> 
> unused devices: <none>
> 
> but the re-added device isn't added to the MD RAID.
> In fact, it has been assigned a _different_ namespace ID:
> 
> [  904.299065] pcieport 0000:00:08.0: pciehp: Slot(0-1): Card present
> [  904.299067] pcieport 0000:00:08.0: pciehp: Slot(0-1): Link Up
> [  904.435314] pci 0000:02:00.0: [8086:5845] type 00 class 0x010802
> [  904.435523] pci 0000:02:00.0: reg 0x10: [mem 0x00000000-0x00001fff 
> 64bit]
> [  904.435676] pci 0000:02:00.0: reg 0x20: [mem 0x00000000-0x00000fff]
> [  904.436982] pci 0000:02:00.0: BAR 0: assigned [mem 
> 0xc1200000-0xc1201fff 64bit]
> [  904.437086] pci 0000:02:00.0: BAR 4: assigned [mem 
> 0xc1202000-0xc1202fff]
> [  904.437118] pcieport 0000:00:08.0: PCI bridge to [bus 02]
> [  904.437137] pcieport 0000:00:08.0:   bridge window [io  0x7000-0x7fff]
> [  904.439024] pcieport 0000:00:08.0:   bridge window [mem 
> 0xc1200000-0xc13fffff]
> [  904.440229] pcieport 0000:00:08.0:   bridge window [mem 
> 0x802000000-0x803ffffff 64bit pref]
> [  904.447150] nvme nvme3: pci function 0000:02:00.0
> [  904.447487] nvme 0000:02:00.0: enabling device (0000 -> 0002)
> [  904.458880] nvme nvme3: 1/0/0 default/read/poll queues
> [  904.461296] nvme1n2: detected capacity change from 0 to 4294967296
> 
> and the 'old', pre-hotplug device still lingers on in the 'nvme list' 
> output.
> 
Compare that to the 'standard', non-CMIC nvme, where with the same setup 
MD would detach the nvme on its own:

# cat /proc/mdstat
Personalities : [raid10]
md127 : active (auto-read-only) raid10 nvme2n1[1]
       4189184 blocks super 1.2 2 near-copies [2/1] [_U]
       bitmap: 0/1 pages [0KB], 65536KB chunk

unused devices: <none>
# nvme list
Node             SN                   Model 
       Namespace Usage                      Format           FW Rev
---------------- -------------------- 
---------------------------------------- --------- 
-------------------------- ---------------- --------
/dev/nvme0n1     SLESNVME1            QEMU NVMe Ctrl 
       1          17.18  GB /  17.18  GB    512   B +  0 B   1.0
/dev/nvme2n1     SLESNVME3            QEMU NVMe Ctrl 
       1           4.29  GB /   4.29  GB    512   B +  0 B   1.0

And yes, this is exactly the same setup, the only difference being the 
CMIC setting for the NVMe device.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

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