From 6b7c1815e1c89cb66ff48fbba6da69fe6d254630 Mon Sep 17 00:00:00 2001 From: Fiona Ebner Date: Mon, 11 Dec 2023 14:28:38 +0100 Subject: [PATCH] add patch to work around stuck guest IO with iothread and VirtIO block/SCSI When using iothread, after commits 1665d9326f ("virtio-blk: implement BlockDevOps->drained_begin()") 766aa2de0f ("virtio-scsi: implement BlockDevOps->drained_begin()") it can happen that polling gets stuck when draining. This would cause IO in the guest to get completely stuck. A workaround for users is stopping and resuming the vCPUs because that would also stop and resume the dataplanes which would kick the host notifiers. This can happen with block jobs like backup and drive mirror as well as with hotplug [2]. Reports in the community forum that might be about this issue[0][1] and there is also one in the enterprise support channel. As a workaround in the code, just re-enable notifications and kick the virt queue after draining. Draining is already costly and rare, so no need to worry about a performance penalty here. This was taken from the following comment of a QEMU developer [3] (in my debugging, I had already found re-enabling notification to work around the issue, but also kicking the queue is more complete). [0]: https://forum.proxmox.com/threads/137286/ [1]: https://forum.proxmox.com/threads/137536/ [2]: https://issues.redhat.com/browse/RHEL-3934 [3]: https://issues.redhat.com/browse/RHEL-3934?focusedId=23562096&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-23562096 Signed-off-by: Fiona Ebner --- ...work-around-iothread-polling-getting.patch | 66 +++++++++++++++++++ debian/patches/series | 1 + 2 files changed, 67 insertions(+) create mode 100644 debian/patches/pve/0046-virtio-blk-scsi-work-around-iothread-polling-getting.patch diff --git a/debian/patches/pve/0046-virtio-blk-scsi-work-around-iothread-polling-getting.patch b/debian/patches/pve/0046-virtio-blk-scsi-work-around-iothread-polling-getting.patch new file mode 100644 index 0000000..3ac10a8 --- /dev/null +++ b/debian/patches/pve/0046-virtio-blk-scsi-work-around-iothread-polling-getting.patch @@ -0,0 +1,66 @@ +From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001 +From: Fiona Ebner +Date: Tue, 5 Dec 2023 14:05:49 +0100 +Subject: [PATCH] virtio blk/scsi: work around iothread polling getting stuck + with drain + +When using iothread, after commits +1665d9326f ("virtio-blk: implement BlockDevOps->drained_begin()") +766aa2de0f ("virtio-scsi: implement BlockDevOps->drained_begin()") +it can happen that polling gets stuck when draining. This would cause +IO in the guest to get completely stuck. + +A workaround for users is stopping and resuming the vCPUs because that +would also stop and resume the dataplanes which would kick the host +notifiers. + +This can happen with block jobs like backup and drive mirror as well +as with hotplug [2]. + +Reports in the community forum that might be about this issue[0][1] +and there is also one in the enterprise support channel. + +As a workaround in the code, just re-enable notifications and kick the +virt queue after draining. Draining is already costly and rare, so no +need to worry about a performance penalty here. This was taken from +the following comment of a QEMU developer [3] (in my debugging, +I had already found re-enabling notification to work around the issue, +but also kicking the queue is more complete). + +[0]: https://forum.proxmox.com/threads/137286/ +[1]: https://forum.proxmox.com/threads/137536/ +[2]: https://issues.redhat.com/browse/RHEL-3934 +[3]: https://issues.redhat.com/browse/RHEL-3934?focusedId=23562096&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-23562096 + +Signed-off-by: Fiona Ebner +--- + hw/block/virtio-blk.c | 2 ++ + hw/scsi/virtio-scsi.c | 2 ++ + 2 files changed, 4 insertions(+) + +diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c +index 39e7f23fab..22502047d5 100644 +--- a/hw/block/virtio-blk.c ++++ b/hw/block/virtio-blk.c +@@ -1537,6 +1537,8 @@ static void virtio_blk_drained_end(void *opaque) + for (uint16_t i = 0; i < s->conf.num_queues; i++) { + VirtQueue *vq = virtio_get_queue(vdev, i); + virtio_queue_aio_attach_host_notifier(vq, ctx); ++ virtio_queue_set_notification(vq, 1); ++ virtio_queue_notify(vdev, i); + } + } + +diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c +index 45b95ea070..a7bddbf899 100644 +--- a/hw/scsi/virtio-scsi.c ++++ b/hw/scsi/virtio-scsi.c +@@ -1166,6 +1166,8 @@ static void virtio_scsi_drained_end(SCSIBus *bus) + for (uint32_t i = 0; i < total_queues; i++) { + VirtQueue *vq = virtio_get_queue(vdev, i); + virtio_queue_aio_attach_host_notifier(vq, s->ctx); ++ virtio_queue_set_notification(vq, 1); ++ virtio_queue_notify(vdev, i); + } + } + diff --git a/debian/patches/series b/debian/patches/series index 9938b8e..0e21f1f 100644 --- a/debian/patches/series +++ b/debian/patches/series @@ -59,3 +59,4 @@ pve/0042-Revert-block-rbd-implement-bdrv_co_block_status.patch pve/0043-alloc-track-fix-deadlock-during-drop.patch pve/0044-migration-for-snapshots-hold-the-BQL-during-setup-ca.patch pve/0045-savevm-async-don-t-hold-BQL-during-setup.patch +pve/0046-virtio-blk-scsi-work-around-iothread-polling-getting.patch