99c80e7492
As reported in the community forum [0], doing a snapshot without saving the VM state for a VM with a VirtIO block device with iothread would lead to an assertion failure [1] and thus crash. The issue is that vm_start() is called from the coroutine qmp_savevm_end() which violates assumptions about graph locking down the line. Factor out the part of qmp_savevm_end() that actually needs to be a coroutine into a separate helper and turn qmp_savevm_end() into a non-coroutine, so that it can call vm_start() safely. The issue is likely not new, but was exposed by the recent graph locking rework introducing stricter checks. The issue does not occur when saving the VM state, because then the non-coroutine process_savevm_finalize() will already call vm_start() before qmp_savevm_end(). [0]: https://forum.proxmox.com/threads/149883/ [1]: > #0 0x00007353e6096e2c __pthread_kill_implementation (libc.so.6 + 0x8ae2c) > #1 0x00007353e6047fb2 __GI_raise (libc.so.6 + 0x3bfb2) > #2 0x00007353e6032472 __GI_abort (libc.so.6 + 0x26472) > #3 0x00007353e6032395 __assert_fail_base (libc.so.6 + 0x26395) > #4 0x00007353e6040eb2 __GI___assert_fail (libc.so.6 + 0x34eb2) > #5 0x0000592002307bb3 bdrv_graph_rdlock_main_loop (qemu-system-x86_64 + 0x83abb3) > #6 0x00005920022da455 bdrv_change_aio_context (qemu-system-x86_64 + 0x80d455) > #7 0x00005920022da6cb bdrv_try_change_aio_context (qemu-system-x86_64 + 0x80d6cb) > #8 0x00005920022fe122 blk_set_aio_context (qemu-system-x86_64 + 0x831122) > #9 0x00005920021b7b90 virtio_blk_start_ioeventfd (qemu-system-x86_64 + 0x6eab90) > #10 0x0000592002022927 virtio_bus_start_ioeventfd (qemu-system-x86_64 + 0x555927) > #11 0x0000592002066cc4 vm_state_notify (qemu-system-x86_64 + 0x599cc4) > #12 0x000059200205d517 vm_prepare_start (qemu-system-x86_64 + 0x590517) > #13 0x000059200205d56b vm_start (qemu-system-x86_64 + 0x59056b) > #14 0x00005920020a43fd qmp_savevm_end (qemu-system-x86_64 + 0x5d73fd) > #15 0x00005920023f3749 qmp_marshal_savevm_end (qemu-system-x86_64 + 0x926749) > #16 0x000059200242f1d8 qmp_dispatch (qemu-system-x86_64 + 0x9621d8) > #17 0x000059200238fa98 monitor_qmp_dispatch (qemu-system-x86_64 + 0x8c2a98) > #18 0x000059200239044e monitor_qmp_dispatcher_co (qemu-system-x86_64 + 0x8c344e) > #19 0x000059200245359b coroutine_trampoline (qemu-system-x86_64 + 0x98659b) > #20 0x00007353e605d9c0 n/a (libc.so.6 + 0x519c0) Signed-off-by: Fiona Ebner <f.ebner@proxmox.com> |
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