From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate001.proxmox.com (gate001.proxmox.com [IPv6:2a0f:8001:1:32::40]) by lore.proxmox.com (Postfix) with ESMTPS id 3CB861FF09B for ; Mon, 14 Sep 2026 12:47:15 +0200 (CEST) Received: from gate001.proxmox.com (localhost.localdomain [127.0.0.1]) by gate001.proxmox.com (Proxmox) with ESMTP id 092D921641; Mon, 14 Sep 2026 12:46:52 +0200 (CEST) From: Erik Fastermann To: pve-devel@lists.proxmox.com Subject: [PATCH qemu v3 0/4] savevm-async: fix stuck paused vm after snapshot Date: Mon, 14 Sep 2026 12:46:38 +0200 Message-ID: <20260914104642.145478-1-e.fastermann@proxmox.com> X-Mailer: git-send-email 2.47.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-SPAM-LEVEL: Spam detection results: 1 AWL -0.433 Adjusted score from AWL reputation of From: address DMARC_MISSING 0.1 Missing DMARC policy KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment (newer systems) KAM_LAZY_DOMAIN_SECURITY 1 Sending domain does not have any anti-forgery methods RDNS_NONE 1.274 Delivered to internal network by a host with no rDNS SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record SPF_NONE 0.001 SPF: sender does not publish an SPF Record Message-ID-Hash: LE3WXISLWRI4ZOBS6GDWIIDEII2MGGC2 X-Message-ID-Hash: LE3WXISLWRI4ZOBS6GDWIIDEII2MGGC2 X-MailFrom: efastermann@ruth.proxmox.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; loop; banned-address; emergency; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: Erik Fastermann X-Mailman-Version: 3.3.10 Precedence: list List-Id: Proxmox VE development discussion List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: Snapshotting a paused VM left it in finish-migrate, where it stayed until the VM was restarted. Fix this by storing the run state instead and put it back, similar to migration_iteration_finish(). While working on that, I noticed some memory leaks and other issues, which I found by using sanitizer tools like ASAN and reading the code and docs. Changes since the RFC: * store the run state via runstate_get() and restore it instead of skipping the transition into finish-migrate (Thanks @Fiona) * refuse a snapshot while an incoming migration is pending, which migrate_prepare() already does, otherwise the restore aborts * fixed multiple memory leaks * fixed multiple discarded error messages * removed raw uses of allocators * folded the changes into the relevant debian/patches Changes since v2 (Thanks @Fiona for the feedback): * dropped patches 1-5, which were already applied [3] * guard migration_state_cleanup() in qmp_savevm_start() failure case * added comment when attempting to set RUN_STATE_SAVE_VM Future work: * Fiona mentioned that similar bugs to the ones I found also exist in upstream QEMU. I will look into submitting patches. * Once SAVE_STATE_ERROR is set, no new snapshot can be started and savevm-start fails with "VM snapshot already started" until the VM is restarted. Resetting that state looks difficult and could introduce new bugs. A couple of people ran into this before, see [0] and [1]. It would definitely be nicer if a single failed snapshot did not block further snapshots until a VM restart. I added a Bugzilla entry [4]. * TSAN flags a data race on snap_state.bs_pos. Probably simply fixed by using atomics. There might be some other issues in savevm-async, but that has to be checked in more detail. I added a Bugzilla entry [5]. Note that patch 4 touches the same lines as [2]. [0] https://forum.proxmox.com/threads/snapshot-creation-issue.176090/ [1] https://forum.proxmox.com/threads/snapshot-fails-to-cleanup-and-prevents-future-snapshots.144757/ [2] https://lore.proxmox.com/all/20260714142629.277917-2-f.ebner@proxmox.com/ [3] https://lore.proxmox.com/pve-devel/20260907094744.131193-1-e.fastermann@proxmox.com/ [4] https://bugzilla.proxmox.com/show_bug.cgi?id=8037 [5] https://bugzilla.proxmox.com/show_bug.cgi?id=8038 Erik Fastermann (4): savevm-async: free migration vmdesc savevm-async: release resources on start failure path savevm-async: include reason when file open fails savevm-async: restore run state from before snapshot ...async-for-background-state-snapshots.patch | 116 ++++++++++++++---- ...add-optional-buffer-size-to-QEMUFile.patch | 6 +- ...se-migration-blocker-check-for-snaps.patch | 4 +- 3 files changed, 94 insertions(+), 32 deletions(-) -- 2.47.3