Date: Tue, 15 Oct 2024 14:31:42 -0400 From: seneca@vybenetworks.com To: freebsd-questions@freebsd.org Subject: Re: ZFS Rename rebooting server Message-ID: <29467b51cd7c5c28e09bdcc38b52f0de@vybenetworks.com> In-Reply-To: <6250644a-8e4a-4f44-bea5-068be84640c3@druid.net> References: <6250644a-8e4a-4f44-bea5-068be84640c3@druid.net>
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On 14.10.2024 17:32, D'Arcy Cain wrote: > I have never seen this before. I am running bhyve on ZFS and I want to > rename the VM. I shut down the server and do "zfs rename old new" and > BOOM! it reboots. No wait, just immediate. In short, that server had a kernel panic that appears to be related to OpenZFS issue #16274: "Kernel oops (null pointer dereference) when renaming a zvol, if snapdev=visible AND the zvol has at least one snapshot". For reference, it currently runs 14.1-RELEASE-p5. > Anyone know how to debug something like this? I started by connecting to the server's built-in remote KVM. From it, I saw, and photographed, the rather distinctive output generated by a kernel panic (a page fault) resulting from a zfs rename attempt. A quick search online using more general terms was not useful, so I then went to OpenZFS' Github repository and searched for issues that included the term 'z_zvol', the name of the panic's current process. Issue #16274 was near the top of the returned list, and the conditions mentioned in the title matched the conditions on the server and zfs rename in question. From the longer comment thread in the issue, I saw a rather similar stack trace to the one from the server (although Linux, not FreeBSD), using the same version of OpenZFS as FreeBSD 14.1, and a confirmation that the issue affected FreeBSD 15. This issue is triggered specifically by trying to rename zvols with snapshots and snapdev=visible. I then set snapdev=hidden on the zvol to be renamed and watched another attempt at renaming it. This time, the zfs rename succeeded with no panic. -- Seneca Cunningham
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