NFS4: Sequence Misordered

Scan Type: Errors, Severity: High

Column value nfs.opcode: operation number

Column value nfs.nfsstat4: returned result  

https://www.rfc-editor.org/rfc/rfc8881

NFS4ERR_SEQ_MISORDERED (Error Code 10063)

The requester sent a Sequence operation with an invalid sequence ID.

A slot contains a sequence ID and the cached reply corresponding to the request sent with that sequence ID. The sequence ID is a 32-bit unsigned value, and is therefore in the range 0..0xFFFFFFFF (232 - 1). The first time a slot is used, the requester MUST specify a sequence ID of one (Section 18.36). Each time a slot is reused, the request MUST specify a sequence ID that is one greater than that of the previous request on the slot. If the previous sequence ID was 0xFFFFFFFF, then the next request for the slot MUST have the sequence ID set to zero (i.e., (232 - 1) + 1 mod 232).

The sequence ID accompanies the slot ID in each request. It is for the critical check at the replier: it used to efficiently determine whether a request using a certain slot ID is a retransmit or a new, never-before-seen request. It is not feasible for the requester to assert that it is retransmitting to implement this, because for any given request the requester cannot know whether the replier has seen it unless the replier actually replies. Of course, if the requester has seen the reply, the requester would not retransmit.

The replier compares each received request's sequence ID with the last one previously received for that slot ID, to see if the new request is:

• A new request, in which the sequence ID is one greater than that previously seen in the slot (accounting for sequence wraparound). The replier proceeds to execute the new request, and the replier MUST increase the slot's sequence ID by one.

• A retransmitted request, in which the sequence ID is equal to that currently recorded in the slot. If the original request has executed to completion, the replier returns the cached reply. See Section 2.10.6.2 for direction on how the replier deals with retries of requests that are still in progress.

• A misordered retry, in which the sequence ID is less than (accounting for sequence wraparound) that previously seen in the slot. The replier MUST return NFS4ERR_SEQ_MISORDERED (as the result from SEQUENCE or CB_SEQUENCE).

• A misordered new request, in which the sequence ID is two or more than (accounting for sequence wraparound) that previously seen in the slot. Note that because the sequence ID MUST wrap around to zero once it reaches 0xFFFFFFFF, a misordered new request and a misordered retry cannot be distinguished. Thus, the replier MUST return NFS4ERR_SEQ_MISORDERED (as the result from SEQUENCE or CB_SEQUENCE).

Scenario #1

https://access.redhat.com/solutions/6934561

NFS client goes into SEQUENCE/NFS4ERR_SEQ_MISORDERED loop

Scenario #2

https://access.redhat.com/solutions/5738871

NFS v4.1 mount stuck, which freezes qemu-kvm

Workaround:

Sequence command is introduced from nfsv4.1.

Try to change nfs version to 4.0 or 3.0.

www.traceinside.com