[LU-17665] LNet: lock primary NID only on a peer constructed by Lustre

• Type: Improvement
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.16.0
• Labels: Multi-Rail lnet
• Severity: 3
• Assignee: Serguei Smirnov
• Reporter: Serguei Smirnov

Description

Primary NID locking is useful when client is connecting to a server and peer representation is provided to LNet by Lustre via LNetAddPeer API - as interpreted from the mount command string or llog.

When the server responds to a client, there's no need to lock the client's primary NID.

Comments

[Peter Jones]

Merged for 2.16

[Gerrit Updater]

"Oleg Drokin <[e-mail]>" merged in patch https://review.whamcloud.com/c/fs/lustre-release/+/54539/
Subject: LU-17665 lnet: lock primary NID only on lustre-built peer
Project: fs/lustre-release
Branch: master
Current Patch Set:
Commit: 90ec7361b756e685572bd168643d61bb2f4a85c4

[Serguei Smirnov]

The client can go away and come back later with a different set of NIDs. With the server locking client NIDs, it is possible that NID which used to belong to the client and got locked as primary on the server now belongs to a different client. The server will attempt to merge peer records, but may be unable to do it properly because deleting of the primary NID is not allowed.

Let square brackets designate actual node configuration and round brackets - LNet view of the peer. For example, suppose the client with NIDs [A,B] connects to the server. The server creates peer record (pA,B) where NID A is primary. Then the same client goes away and comes back only with NID B configured. This results in "[B] -  (pA,B)" because the server won't delete the locked NID A for the client. If another client comes up with NID A configured, there will be a conflict because the server will delete NID B from the existing peer record, so the original peer is kind of hijacked for the new client: "[A] - (pA), [B] - ?".

Not sure exactly what this may cause from the FS point of view, but it looks wrong. The 54539 patch is trying to avoid such confusion by making sure that the server discovers the client NIDs before using them.

[Gerrit Updater]

"Serguei Smirnov <[e-mail]>" uploaded a new patch: https://review.whamcloud.com/c/fs/lustre-release/+/54539
Subject: LU-17665 lnet: lock primary NID only on lustre-built peer
Project: fs/lustre-release
Branch: master
Current Patch Set: 1
Commit: 39595d9fbf64d8b2d16e3ddd9db7dbd05abc5e40