Saw I/O errors while delete/create/attach a namespace on nvme device.

[Wen Xiong]

> To check exactly which id is problematic something like in [1] can be
> used, totally untested ...
> 
Steps:
# nvme detach-ns /dev/nvme0 --namespace-id=1 --controllers=0x81
# nvme delete-ns /dev/nvme0 --namespace-id=1
# nvme create-ns /dev/nvme0 --nsze=562805846 --ncap=562805846 --flbas=0 
-dps=0 -nmic=1
# nvme attach-ns /dev/nvme0 -n 1  --controller=0x81

Below is linux log with your patch:

[  149.570987] nvme nvme0: rescanning namespaces.
[  149.578714] nguid mismatch
[  149.578719] nvme nvme0: identifiers changed for nsid 1
[  149.582291] block nvme0n1: no usable path - requeuing I/O
[  149.722140] block nvme0n1: no available path - failing I/O
[  149.722157] block nvme0n1: no available path - failing I/O
[  149.722165] Buffer I/O error on dev nvme0n1, logical block 281402912, 
async page read
[  149.722171] block nvme0n1: no available path - failing I/O
[  149.722175] Buffer I/O error on dev nvme0n1, logical block 281402913, 
async page read
[  149.722181] block nvme0n1: no available path - failing I/O
[  149.722185] Buffer I/O error on dev nvme0n1, logical block 281402914, 
async page read
[  149.722191] block nvme0n1: no available path - failing I/O
[  149.722195] Buffer I/O error on dev nvme0n1, logical block 281402915, 
async page read
[  149.722203] block nvme0n1: no available path - failing I/O
[  149.722208] Buffer I/O error on dev nvme0n1, logical block 281402916, 
async page read
[  149.722217] block nvme0n1: no available path - failing I/O
[  149.722226] Buffer I/O error on dev nvme0n1, logical block 281402917, 
async page read
[  149.722231] block nvme0n1: no available path - failing I/O
[  149.722233] Buffer I/O error on dev nvme0n1, logical block 281402918, 
async page read
[  149.722237] block nvme0n1: no available path - failing I/O
[  149.722239] Buffer I/O error on dev nvme0n1, logical block 281402919, 
async page read
[root at ltcrain119-lp4 ~]#

Below is nguid changes:
# nvme id-ns /dev/nvme0n1|grep nguid
nguid   : 37444630577000630025384700000245

  nvme id-ns /dev/nvme0n1|grep nguid
nguid   : 37444630577000630025384700000246

Thanks a lot!
Wendy