Hi,
After the VM boots up, I always get the below call-trace when I run "nload" for the first time:
[ 113.910911] WARNING: suspicious RCU usage
[ 113.913244] 5.2.0+ #19 Not tainted
[ 113.915216] -----------------------------
[ 113.917521] drivers/net/hyperv/netvsc_drv.c:1243 suspicious rcu_dereference_check() usage!
[ 113.922191]
[ 113.922191] other info that might help us debug this:
[ 113.926573]
[ 113.926573] rcu_scheduler_active = 2, debug_locks = 1
[ 113.930052] 4 locks held by nload/1977:
[ 113.932251] #0: 0000000080b71e86 (&p->lock){+.+.}, at: seq_read+0x41/0x3d0
[ 113.936115] #1: 00000000cacff770 (&of->mutex){+.+.}, at: kernfs_seq_start+0x2a/0x90
[ 113.940115] #2: 00000000287c988f (kn->count#134){.+.+}, at: kernfs_seq_start+0x32/0x90
[ 113.944292] #3: 00000000996fa9cc (dev_base_lock){++.+}, at: netstat_show.isra.25+0x4a/0xb0
[ 113.958076]
[ 113.958076] stack backtrace:
[ 113.958081] CPU: 3 PID: 1977 Comm: nload Not tainted 5.2.0+ #19
[ 113.958083] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS 090006 04/28/2016
[ 113.958084] Call Trace:
[ 113.958091] dump_stack+0x67/0x90
[ 113.973663] netvsc_get_stats64+0x159/0x170 [hv_netvsc]
[ 113.973663] dev_get_stats+0x55/0xb0
[ 113.973663] netstat_show.isra.25+0x5b/0xb0
[ 113.973663] dev_attr_show+0x15/0x40
[ 113.981661] sysfs_kf_seq_show+0xad/0xf0
[ 113.981661] seq_read+0x146/0x3d0
[ 113.981661] vfs_read+0x9c/0x160
[ 113.989025] ksys_read+0x5c/0xd0
[ 113.989025] do_syscall_64+0x5e/0x220
[ 113.989025] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 113.989025] RIP: 0033:0x7f4485daaf31
nload is a console application which monitors network traffic and bandwidth usage in real time.
The warning is caused by the rcu_dereference_rtnl() :
1239 static void netvsc_get_stats64(struct net_device *net,
1240 struct rtnl_link_stats64 *t)
1241 {
1242 struct net_device_context *ndev_ctx = netdev_priv(net);
1243 struct netvsc_device *nvdev = rcu_dereference_rtnl(ndev_ctx->nvdev);
I think here netvsc_get_stats64() neither holds rcu_read_lock() nor RTNL
IMO it should call rcu_read_lock()/unlock(), or get RTNL to fix the warning?
Thanks,
-- Dexuan
