kernel null pointer at nvme_tcp_init_iter+0x7d/0xd0 [nvme_tcp]

[Sagi Grimberg]

>> So it's nvme_admin_abort_cmd here
>>
>> [   74.017450] run blktests nvme/012 at 2021-02-09 21:41:55
>> [   74.111311] loop: module loaded
>> [   74.125717] loop0: detected capacity change from 2097152 to 0
>> [   74.141026] nvmet: adding nsid 1 to subsystem blktests-subsystem-1
>> [   74.149395] nvmet_tcp: enabling port 0 (127.0.0.1:4420)
>> [   74.158298] nvmet: creating controller 1 for subsystem
>> blktests-subsystem-1 for NQN
>> nqn.2014-08.org.nvmexpress:uuid:41131d88-02ca-4ccc-87b3-6ca3f28b13a4.
>> [   74.158742] nvme nvme0: creating 48 I/O queues.
>> [   74.163391] nvme nvme0: mapped 48/0/0 default/read/poll queues.
>> [   74.184623] nvme nvme0: new ctrl: NQN "blktests-subsystem-1", addr
>> 127.0.0.1:4420
>> [   75.235059] nvme_tcp: rq 38 opcode 8
>> [   75.238653] blk_update_request: I/O error, dev nvme0c0n1, sector
>> 1048624 op 0x9:(WRITE_ZEROES) flags 0x2800800 phys_seg 0 prio class 0
>> [   75.380179] XFS (nvme0n1): Mounting V5 Filesystem
>> [   75.387457] XFS (nvme0n1): Ending clean mount
>> [   75.388555] xfs filesystem being mounted at /mnt/blktests supports
>> timestamps until 2038 (0x7fffffff)
>> [   91.035659] XFS (nvme0n1): Unmounting Filesystem
>> [   91.043334] nvme nvme0: Removing ctrl: NQN "blktests-subsystem-1"
> 
> But write-zeores is also data less command and should not fail.

And it has a bio, which means that nvme-tcp tries to init an iter
for it when it shouldn't. So the actual offending commit is:
cb9b870fba3e, which cleaned up how the iter is initialized but 
introduced this issue.