This bug happens if the VMM sends a VIRTIO_NET_S_ANNOUNCE request while
the virtio-net driver is still probing with rtnl_lock() hold, this will
cause a recursive mutex in netdev_notify_peers().
Fix it by temporarily save the announce status while probing, and then in
virtnet_open(), if it sees a delayed announce work is there, it starts to
schedule the virtnet_config_changed_work().
Another possible solution is to directly check whether rtnl_is_locked()
and call __netdev_notify_peers(), but in that way means we need to relies
on netdev_queue to schedule the arp packets after ndo_open(), which we
thought is not very intuitive.
We've observed a softlockup with Ubuntu 24.04, and can be reproduced with
QEMU sending the announce_self rapidly while booting.
[ 494.167473] INFO: task swapper/0:1 blocked for more than 368 seconds.
[ 494.167667] Not tainted 6.8.0-57-generic #59-Ubuntu
[ 494.167810] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 494.168015] task:swapper/0 state:D stack:0 pid:1 tgid:1 ppid:0 flags:0x00004000
[ 494.168260] Call Trace:
[ 494.168329]
[ 494.168389] __schedule+0x27c/0x6b0
[ 494.168495] schedule+0x33/0x110
[ 494.168585] schedule_preempt_disabled+0x15/0x30
[ 494.168709] __mutex_lock.constprop.0+0x42f/0x740
[ 494.168835] __mutex_lock_slowpath+0x13/0x20
[ 494.168949] mutex_lock+0x3c/0x50
[ 494.169039] rtnl_lock+0x15/0x20
[ 494.169128] netdev_notify_peers+0x12/0x30
[ 494.169240] virtnet_config_changed_work+0x152/0x1a0
[ 494.169377] virtnet_probe+0xa48/0xe00
[ 494.169484] ? vp_get+0x4d/0x100
[ 494.169574] virtio_dev_probe+0x1e9/0x310
[ 494.169682] really_probe+0x1c7/0x410
[ 494.169783] __driver_probe_device+0x8c/0x180
[ 494.169901] driver_probe_device+0x24/0xd0
[ 494.170011] __driver_attach+0x10b/0x210
[ 494.170117] ? __pfx___driver_attach+0x10/0x10
[ 494.170237] bus_for_each_dev+0x8d/0xf0
[ 494.170341] driver_attach+0x1e/0x30
[ 494.170440] bus_add_driver+0x14e/0x290
[ 494.170548] driver_register+0x5e/0x130
[ 494.170651] ? __pfx_virtio_net_driver_init+0x10/0x10
[ 494.170788] register_virtio_driver+0x20/0x40
[ 494.170905] virtio_net_driver_init+0x97/0xb0
[ 494.171022] do_one_initcall+0x5e/0x340
[ 494.171128] do_initcalls+0x107/0x230
[ 494.171228] ? __pfx_kernel_init+0x10/0x10
[ 494.171340] kernel_init_freeable+0x134/0x210
[ 494.171462] kernel_init+0x1b/0x200
[ 494.171560] ret_from_fork+0x47/0x70
[ 494.171659] ? __pfx_kernel_init+0x10/0x10
[ 494.171769] ret_from_fork_asm+0x1b/0x30
[ 494.171875]
Fixes: df28de7b0050 ("virtio-net: synchronize operstate with admin state on up/down")
Signed-off-by: Zigit Zo
---
v1 -> v2:
- Check vi->status in virtnet_open().
v1:
- https://lore.kernel.org/netdev/20250630095109.214013-1-zuozhijie@bytedance.com/
---
drivers/net/virtio_net.c | 43 ++++++++++++++++++++++++----------------
1 file changed, 26 insertions(+), 17 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index e53ba600605a..859add98909b 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3151,6 +3151,10 @@ static int virtnet_open(struct net_device *dev)
if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_STATUS)) {
if (vi->status & VIRTIO_NET_S_LINK_UP)
netif_carrier_on(vi->dev);
+ if (vi->status & VIRTIO_NET_S_ANNOUNCE) {
+ vi->status &= ~VIRTIO_NET_S_ANNOUNCE;
+ schedule_work(&vi->config_work);
+ }
virtio_config_driver_enable(vi->vdev);
} else {
vi->status = VIRTIO_NET_S_LINK_UP;
@@ -6215,33 +6219,34 @@ static void virtnet_config_changed_work(struct work_struct *work)
{
struct virtnet_info *vi =
container_of(work, struct virtnet_info, config_work);
- u16 v;
+ u16 v, changed;
if (virtio_cread_feature(vi->vdev, VIRTIO_NET_F_STATUS,
struct virtio_net_config, status, &v) < 0)
return;
- if (v & VIRTIO_NET_S_ANNOUNCE) {
+ changed = vi->status ^ v;
+
+ /* Assume the device will clear announce status when ack received. */
+ if ((changed & VIRTIO_NET_S_ANNOUNCE) && (v & VIRTIO_NET_S_ANNOUNCE)) {
netdev_notify_peers(vi->dev);
virtnet_ack_link_announce(vi);
+ v &= ~VIRTIO_NET_S_ANNOUNCE;
}
- /* Ignore unknown (future) status bits */
- v &= VIRTIO_NET_S_LINK_UP;
-
- if (vi->status == v)
- return;
-
- vi->status = v;
-
- if (vi->status & VIRTIO_NET_S_LINK_UP) {
- virtnet_update_settings(vi);
- netif_carrier_on(vi->dev);
- netif_tx_wake_all_queues(vi->dev);
- } else {
- netif_carrier_off(vi->dev);
- netif_tx_stop_all_queues(vi->dev);
+ if (changed & VIRTIO_NET_S_LINK_UP) {
+ if (v & VIRTIO_NET_S_LINK_UP) {
+ virtnet_update_settings(vi);
+ netif_carrier_on(vi->dev);
+ netif_tx_wake_all_queues(vi->dev);
+ } else {
+ netif_carrier_off(vi->dev);
+ netif_tx_stop_all_queues(vi->dev);
+ }
}
+
+ /* Ignore unknown (future) status bits */
+ vi->status = v & (VIRTIO_NET_S_LINK_UP | VIRTIO_NET_S_ANNOUNCE);
}
static void virtnet_config_changed(struct virtio_device *vdev)
@@ -7030,6 +7035,10 @@ static int virtnet_probe(struct virtio_device *vdev)
otherwise get link status from config. */
netif_carrier_off(dev);
if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_STATUS)) {
+ /* If there's (rarely) an announcement, the actual work will be
+ * scheduled on ndo_open() to avoid recursive rtnl_lock() here.
+ */
+ vi->status = VIRTIO_NET_S_ANNOUNCE;
virtnet_config_changed_work(&vi->config_work);
} else {
vi->status = VIRTIO_NET_S_LINK_UP;
base-commit: 34a500caf48c47d5171f4aa1f237da39b07c6157
--
2.49.0