v4.15-rc5 warning: suspicious RCU usage in net/wireless/util.c:778

[Dominik Brodowski]

On Fri, Dec 22, 2017 at 08:20:12AM +0100, Dominik Brodowski wrote:
> Dear all,
> 
> once the (wifi) link becomes ready, the following warning is emitted on
> mainline (v4.15-rc4-202-gead68f216110) on my notebook:

... and it is still present as of v4.15-rc5-149-g5aa90a845892

> [   22.770422] IPv6: ADDRCONF(NETDEV_CHANGE): wlan0: link becomes ready
> 
> [   22.772364] =============================
> [   22.772369] WARNING: suspicious RCU usage
> [   22.772375] 4.15.0-rc4+ #5 Not tainted
> [   22.772380] -----------------------------
> [   22.772386] /home/brodo/local/kernel/git/linux/net/wireless/util.c:778 suspicious rcu_dereference_check() usage!
> [   22.772391] 
> [   22.772397] 
> [   22.772402] 4 locks held by wpa_supplicant/774:
> [   22.772407]  #0:  (cb_lock){++++}, at: [<00000000276dc3a0>] genl_rcv+0x15/0x40
> [   22.772437]  #1:  (genl_mutex){+.+.}, at: [<0000000024d83eb3>] genl_rcv_msg+0x7a/0x90
> [   22.772463]  #2:  (rtnl_mutex){+.+.}, at: [<000000009de25a59>] nl80211_pre_doit+0xe9/0x190
> [   22.772489]  #3:  (&wdev->mtx){+.+.}, at: [<0000000089bf2cfd>] nl80211_send_iface+0x317/0x8d0
> [   22.772516] 
> [   22.772522] CPU: 3 PID: 774 Comm: wpa_supplicant Not tainted 4.15.0-rc4+ #5
> [   22.772528] Hardware name: Dell Inc. XPS 13 9343/0TM99H, BIOS A11 12/08/2016
> [   22.772532] Call Trace:
> [   22.772544]  dump_stack+0x67/0x95
> [   22.772553]  ieee80211_bss_get_ie+0x66/0x70
> [   22.772562]  nl80211_send_iface+0x344/0x8d0
> [   22.772585]  nl80211_get_interface+0x4b/0xa0
> [   22.772598]  genl_family_rcv_msg+0x32e/0x3f0
> [   22.772607]  ? preempt_count_sub+0x92/0xd0
> [   22.772645]  genl_rcv_msg+0x47/0x90
> [   22.772652]  ? genl_family_rcv_msg+0x3f0/0x3f0
> [   22.772661]  netlink_rcv_skb+0x8a/0x120
> [   22.772677]  genl_rcv+0x24/0x40
> [   22.772684]  netlink_unicast+0x174/0x1f0
> [   22.772698]  netlink_sendmsg+0x386/0x3d0
> [   22.772719]  sock_sendmsg+0x2d/0x40
> [   22.772728]  ___sys_sendmsg+0x2a7/0x300
> [   22.772748]  ? netlink_sendmsg+0x13d/0x3d0
> [   22.772791]  ? __sys_sendmsg+0x67/0xb0
> [   22.772797]  __sys_sendmsg+0x67/0xb0
> [   22.772822]  entry_SYSCALL_64_fastpath+0x18/0x85
> 
> This warning wasn't present in 4.15. Despite of it, networking seems to
> work fine. Nonetheless, the code seems to need a bugfix.

Thanks,
	Dominik