Description of problem:

A VM with virtio-gpu, will produce the following kernel error on display resize:


[   39.103635] ------------[ cut here ]------------
[   39.103659] WARNING: CPU: 7 PID: 67 at drivers/gpu/drm/drm_atomic_helper.c:1549 drm_atomic_helper_commit_hw_done+0xa6/0xb0 [drm_kms_helper]
[   39.103661] Modules linked in: fuse uinput nf_conntrack_netbios_ns nf_conntrack_broadcast ip6t_REJECT nf_reject_ipv6 ip6t_rpfilter xt_conntrack ip_set nfnetlink ebtable_nat ebtable_broute bridge stp llc ip6table_mangle ip6table_security ip6table_nat nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_raw iptable_mangle iptable_security iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_raw ebtable_filter ebtables ip6table_filter ip6_tables acpi_cpufreq tpm_tis tpm_tis_core tpm snd_intel8x0 snd_ac97_codec ac97_bus crct10dif_pclmul snd_seq snd_seq_device ppdev snd_pcm virtio_gpu ttm snd_timer crc32_pclmul drm_kms_helper 9pnet_virtio drm ghash_clmulni_intel parport_pc snd 9pnet virtio_balloon parport joydev i2c_piix4 pcspkr soundcore nfsd qemu_fw_cfg auth_rpcgss nfs_acl
[   39.103798]  lockd grace sunrpc 8139too virtio_console crc32c_intel serio_raw 8139cp virtio_pci mii ata_generic virtio_ring pata_acpi virtio floppy
[   39.103822] CPU: 7 PID: 67 Comm: kworker/7:0 Tainted: G        W       4.8.0+ #2
[   39.103824] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-1.fc26 04/01/2014
[   39.103857] Workqueue: events drm_mode_rmfb_work_fn [drm]
[   39.103862]  ffffb6dbc0877c08 ffffffffbb3e48bd 0000000000000000 0000000000000000
[   39.103869]  ffffb6dbc0877c48 ffffffffbb0a156b 0000060df36a3000 0000000000000000
[   39.103874]  ffff8a71f96956c0 ffffffffc032e440 ffff8a71fb6f0678 ffff8a71f36c79c0
[   39.103880] Call Trace:
[   39.103892]  [<ffffffffbb3e48bd>] dump_stack+0x63/0x86
[   39.103896]  [<ffffffffbb0a156b>] __warn+0xcb/0xf0
[   39.103900]  [<ffffffffbb0a169d>] warn_slowpath_null+0x1d/0x20
[   39.103916]  [<ffffffffc0323b56>] drm_atomic_helper_commit_hw_done+0xa6/0xb0 [drm_kms_helper]
[   39.103927]  [<ffffffffc033fa7b>] vgdev_atomic_commit_tail+0x4b/0x60 [virtio_gpu]
[   39.103946]  [<ffffffffc03252fc>] commit_tail+0x3c/0x60 [drm_kms_helper]
[   39.103961]  [<ffffffffc03253a5>] drm_atomic_helper_commit+0x85/0xa0 [drm_kms_helper]
[   39.104003]  [<ffffffffc02e3537>] drm_atomic_commit+0x37/0x60 [drm]
[   39.104022]  [<ffffffffc0325b9d>] drm_atomic_helper_set_config+0x7d/0xb0 [drm_kms_helper]
[   39.104056]  [<ffffffffc02d1bb5>] drm_mode_set_config_internal+0x65/0x110 [drm]
[   39.104088]  [<ffffffffc02d1ee6>] drm_framebuffer_remove+0x106/0x150 [drm]
[   39.104117]  [<ffffffffc02d1f73>] drm_mode_rmfb_work_fn+0x43/0x60 [drm]
[   39.104122]  [<ffffffffbb0bb5a4>] process_one_work+0x184/0x430
[   39.104126]  [<ffffffffbb0bba16>] worker_thread+0x1c6/0x490
[   39.104130]  [<ffffffffbb0bb850>] ? process_one_work+0x430/0x430
[   39.104136]  [<ffffffffbb0c1459>] kthread+0xd9/0xf0
[   39.104141]  [<ffffffffbb0c1380>] ? kthread_worker_fn+0x180/0x180
[   39.104146]  [<ffffffffbb808ed5>] ret_from_fork+0x25/0x30
[   39.104150] ---[ end trace e36a9558d55c1954 ]---
[   49.180015] [drm:drm_atomic_helper_commit_cleanup_done [drm_kms_helper]] *ERROR* [CRTC:25:crtc-0] flip_done timed out



The fix exists upstream in 4.9 (eed6f0eda0a), it needs a small adaptation for 4.8:

diff --git a/drivers/gpu/drm/virtio/virtgpu_display.c b/drivers/gpu/drm/virtio/virtgpu_display.c
index 4e192aa..75ec172 100644
--- a/drivers/gpu/drm/virtio/virtgpu_display.c
+++ b/drivers/gpu/drm/virtio/virtgpu_display.c
@@ -338,7 +338,7 @@ static void vgdev_atomic_commit_tail(struct drm_atomic_state *state)
 
        drm_atomic_helper_commit_modeset_disables(dev, state);
        drm_atomic_helper_commit_modeset_enables(dev, state);
-       drm_atomic_helper_commit_planes(dev, state, true);
+       drm_atomic_helper_commit_planes(dev, state, false);