I don't recall seeing a soft lockup at all, not a related one anyway. Sadly I don't have a specific command but I did find it triggered when:
1. Memory is overcommited. It doesn't have to be heavily overcommitted. 2. I/O is very high. 3. I “leave“ an SSH session, releasing a small amount of memory. The patch seems to suggest that it is this release that causes the problem. My guess would be that part of the session is already in the compressed cache, and it is released while another process attempts to enter the compressed cache. I don't even know if that makes sense. To add to the confusion: it crashes fairly consistently across VMs and bare metal, but occasionally a server under the same sort of stress, and otherwise identical setup, can run weeks or months without issue. At this point, though, I know of no specific command to trigger it. If I get time I can have a play around but that may never happen. I usually have zswap.max_pool_percent=50, but everything else can vary and the result is the same. -- 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/1814874 Title: NULL pointer dereference when using z3fold and zswap Status in Linux: Fix Released Status in linux package in Ubuntu: New Bug description: Under memory pressure, my VM locks up. This has been reported upstream though I don't know how far any solution has progressed. https://bugzilla.kernel.org/show_bug.cgi?id=201603 Feb 6 07:15:42 vps632258 kernel: [151336.450064] z3fold: unknown buddy id 0 Feb 6 07:15:42 vps632258 kernel: [151336.454450] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 The little bit of log I managed to salvage is attached. This has happened to two identical VMs. Unusually it has not occurred on a third VM which is configured the same but has less RAM (fingers crossed it won't). Irrelevant information: I thought the lock-ups were due to me using a BTRFS filesystem, however I swapped over to NILFS2 and this still occurs. The only difference seems to be that I am now able to grab some of the kernel output. ProblemType: Bug DistroRelease: Ubuntu 18.04 Package: linux-image-4.18.0-14-generic 4.18.0-14.15~18.04.1 ProcVersionSignature: Ubuntu 4.18.0-14.15~18.04.1-generic 4.18.20 Uname: Linux 4.18.0-14-generic x86_64 ApportVersion: 2.20.9-0ubuntu7.5 Architecture: amd64 Date: Wed Feb 6 10:55:05 2019 ProcEnviron: TERM=xterm PATH=(custom, no user) XDG_RUNTIME_DIR=<set> LANG=en_GB.UTF-8 SHELL=/bin/bash SourcePackage: linux-signed-hwe UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/linux/+bug/1814874/+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
