** Tags removed: verification-needed-disco ** Tags added: verification-done-disco
-- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1828978 Title: NFSv4.1: Interrupted connections cause high bandwidth RPC ping-pong between client and server Status in linux package in Ubuntu: Fix Released Status in linux source package in Disco: Fix Committed Bug description: BugLink: https://bugs.launchpad.net/bugs/1828978 [Impact] There is a bug in NFS v4.1 that causes a large amount of RPC calls between a client and server when a previous RPC call is interrupted. This uses a large amount of bandwidth and can saturate the network. The symptoms are so: * On NFS clients: Attempts to access mounted NFS shares associated with the affected server block indefinitely. * On the network: A storm of repeated RPCs between NFS client and server uses a lot of bandwidth. Each RPC is acknoledged by the server with an NFS4ERR_SEQ_MISORDERED error. * Other NFS clients connected to the same NFS server: Performance drops dramatically. This occurs during a "false retry", when a client attempts to make a new RPC call using a slot+sequence number that references an older, cached call. This happens when a user process interrupts an RPC call that is in progress. [Fix] This was fixed in 5.1 upstream with the below commit: commit 3453d5708b33efe76f40eca1c0ed60923094b971 Author: Trond Myklebust <trond.mykleb...@hammerspace.com> Date: Wed Jun 20 17:53:34 2018 -0400 Subject: NFSv4.1: Avoid false retries when RPC calls are interrupted The fix is to pre-emptively increment the sequence number if an RPC call is interrupted, and to address corner cases we interpret the NFS4ERR_SEQ_MISORDERED error as a sign we need to locate an approperiate sequence number between the value we sent, and the last successfully acked SEQUENCE call. Commit 3453d5708b33efe76f40eca1c0ed60923094b971 is a clean cherry-pick to disco. [Testcase] This is difficult to reproduce on test systems, and has instead been verified on a production NFS v4.1 system in a customer environment. This server is heavily trafficked and has a large number of different NFS clients connected to it. I have built a test kernel that contains the above patch, and also patches for Bug 1842037. It is available here: https://launchpad.net/~mruffell/+archive/ubuntu/sf241068-test Note that the above kernel is for bionic HWE, and not explicitly disco. Discussion about the patch validation can be found at the bottom of Bug 1842037. On unpatched kernels, expect to see the symptoms mentioned in Impact, and on patched systems, everything working as intended. [Regression Potential] The changes are localised to NFS v4.1 only, and other versions of NFS are not affected. If a regression occurs, users can downgrade NFS versions to v4.0 or v3.x until a fix is made. The changes only impact when connections are interrupted, and under typical blue sky scenarios would not be invoked. There have been no fixup commits or commits near the requested commit in newer kernels, which points to this commit fixing the issue, and adopted by the community. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1828978/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
