FYI, we noticed the following commit (built with gcc-7): commit: 4de83b88c66a1e4dba426b29766fb68e61d93792 ("loopback: create blackhole net device similar to loopack.") https://kernel.googlesource.com/pub/scm/linux/kernel/git/next/linux-next.git master in testcase: trinity with following parameters: runtime: 300s test-description: Trinity is a linux system call fuzz tester. test-url: http://codemonkey.org.uk/projects/trinity/ on test machine: qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 2G caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace): +------------------------------------------------------------------------+------------+------------+ | | 8909783cb5 | 4de83b88c6 | +------------------------------------------------------------------------+------------+------------+ | boot_successes | 14 | 0 | | boot_failures | 2 | 10 | | BUG:kernel_hang_in_boot-around-mounting-root_stage | 1 | | | IP-Config:Auto-configuration_of_network_failed | 1 | 1 | | WARNING:suspicious_RCU_usage | 0 | 10 | | include/linux/rtnetlink.h:#suspicious_rcu_dereference_protected()usage | 0 | 10 | +------------------------------------------------------------------------+------------+------------+ If you fix the issue, kindly add following tag Reported-by: kernel test robot [ 14.675051] WARNING: suspicious RCU usage [ 14.675847] 5.2.0-rc6-01699-g4de83b8 #1 Tainted: G T [ 14.676977] ----------------------------- [ 14.677767] include/linux/rtnetlink.h:85 suspicious rcu_dereference_protected() usage! [ 14.679506] [ 14.679506] other info that might help us debug this: [ 14.679506] [ 14.681054] [ 14.681054] rcu_scheduler_active = 2, debug_locks = 1 [ 14.682294] no locks held by swapper/0/1. [ 14.683126] [ 14.683126] stack backtrace: [ 14.684050] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G T 5.2.0-rc6-01699-g4de83b8 #1 [ 14.685659] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 [ 14.687184] Call Trace: [ 14.687749] dump_stack+0x7c/0xc3 [ 14.688437] dev_init_scheduler+0xd7/0x190 [ 14.689246] ? net_olddevs_init+0x5d/0x5d [ 14.690051] ? do_early_param+0xb3/0xb3 [ 14.690821] blackhole_netdev_init+0x42/0x85 [ 14.691647] do_one_initcall+0x17c/0x380 [ 14.692432] ? initcall_blacklisted+0x150/0x150 [ 14.693106] ? lock_downgrade+0x250/0x2b0 [ 14.693106] ? lock_acquire+0x1b6/0x1f0 [ 14.693106] ? do_early_param+0xb3/0xb3 [ 14.693106] kernel_init_freeable+0x3a6/0x45e [ 14.693106] ? rest_init+0x240/0x240 [ 14.693106] kernel_init+0xf/0x120 [ 14.693106] ? _raw_spin_unlock_irq+0x34/0x50 [ 14.693106] ? rest_init+0x240/0x240 [ 14.693106] ret_from_fork+0x24/0x30 [ 14.703089] e1000: Intel(R) PRO/1000 Network Driver - version 7.3.21-k8-NAPI [ 14.704437] e1000: Copyright (c) 1999-2006 Intel Corporation. [ 18.732818] PCI Interrupt Link [LNKC] enabled at IRQ 11 [ 19.159911] e1000 0000:00:03.0 eth0: (PCI:33MHz:32-bit) 52:54:00:12:34:56 [ 19.161267] e1000 0000:00:03.0 eth0: Intel(R) PRO/1000 Network Connection [ 24.301353] rcu-perf: rcu_perf_writer 1 has 100 measurements [ 24.303083] rcu-perf: rcu_perf_writer 0 has 100 measurements [ 24.413125] Dumping ftrace buffer: [ 24.414212] (ftrace buffer empty) [ 24.414980] rcu-perf: Test complete [ 27.308838] e1000 0000:00:03.0 eth0: (PCI:33MHz:32-bit) 52:54:00:12:34:56 [ 27.310641] e1000 0000:00:03.0 eth0: Intel(R) PRO/1000 Network Connection [ 27.313807] usbcore: registered new interface driver usbtmc [ 27.315047] usbcore: registered new interface driver usb-storage [ 27.316263] usbcore: registered new interface driver ums_eneub6250 [ 27.317604] usbcore: registered new interface driver adutux [ 27.318784] usbcore: registered new interface driver appledisplay [ 27.320032] usbcore: registered new interface driver cytherm [ 27.321206] usbcore: registered new interface driver emi26 - firmware loader [ 27.322593] usbcore: registered new interface driver iowarrior [ 27.323906] usbcore: registered new interface driver isight_firmware [ 27.325189] usbcore: registered new interface driver usblcd [ 27.326348] usbcore: registered new interface driver legousbtower [ 27.327594] usbcore: registered new interface driver rio500 [ 27.328824] usbcore: registered new interface driver usbtest [ 27.330009] usbcore: registered new interface driver lvs [ 27.331820] i8042: PNP: PS/2 Controller [PNP0303:KBD,PNP0f13:MOU] at 0x60,0x64 irq 1,12 [ 27.335179] serio: i8042 KBD port at 0x60,0x64 irq 1 [ 27.336854] serio: i8042 AUX port at 0x60,0x64 irq 12 [ 27.340657] input: AT Translated Set 2 keyboard as /devices/platform/i8042/serio0/input/input0 [ 27.345403] usbcore: registered new interface driver xpad [ 27.346683] usbcore: registered new interface driver gtco [ 27.347836] usbcore: registered new interface driver pegasus_notetaker [ 27.350101] mk712: device not present [ 27.351056] usbcore: registered new interface driver usbtouchscreen [ 27.353198] usbcore: registered new interface driver ati_remote2 [ 27.354824] usbcore: registered new interface driver keyspan_remote [ 27.358901] rtc_cmos 00:00: RTC can wake from S4 [ 27.362193] rtc rtc0: alarm rollover: day [ 27.363910] rtc_cmos 00:00: char device (0:0) [ 27.363914] input: AT Translated Set 2 keyboard as /devices/platform/i8042/serio0/input/input1 [ 27.364984] rtc_cmos 00:00: registered as rtc0 [ 27.368376] rtc_cmos 00:00: alarms up to one day, y3k, 114 bytes nvram, hpet irqs [ 27.371730] rtc_cmos 00:00: RTC can wake from S4 [ 27.373382] rtc rtc1: alarm rollover: day [ 27.376906] rtc_cmos 00:00: char device (0:1) [ 27.378153] rtc_cmos 00:00: registered as rtc1 [ 27.379656] rtc_cmos 00:00: alarms up to one day, y3k, 114 bytes nvram, hpet irqs [ 27.384627] i2c /dev entries driver [ 27.385769] i2c-parport-light: adapter type unspecified [ 27.387136] usbcore: registered new interface driver RobotFuzz Open Source InterFace, OSIF [ 27.389221] usbcore: registered new interface driver i2c-tiny-usb [ 27.391172] IR Sharp protocol handler initialized [ 27.392282] ir_imon_decoder: IR iMON protocol handler initialized [ 27.393738] IR RCMM protocol handler initialized [ 27.394834] Driver for 1-wire Dallas network protocol. [ 27.399165] intel_powerclamp: CPU does not support MWAIT [ 27.400646] advantechwdt: WDT driver for Advantech single board computer initialising [ 27.403903] advantechwdt: initialized. timeout=60 sec (nowayout=1) [ 27.405481] ib700wdt: WDT driver for IB700 single board computer initialising [ 27.407789] ib700wdt: START method I/O 443 is not available [ 27.409106] ib700wdt: probe of ib700wdt failed with error -5 [ 27.411021] it87_wdt: no device [ 27.411836] pc87413_wdt: Version 1.1 at io 0x2E [ 27.412931] pc87413_wdt: cannot register miscdev on minor=130 (err=-16) [ 27.414580] w83877f_wdt: I/O address 0x0443 already in use [ 27.415849] w83977f_wdt: driver v1.00 [ 27.416776] w83977f_wdt: cannot register miscdev on minor=130 (err=-16) [ 27.418248] machzwd: MachZ ZF-Logic Watchdog driver initializing [ 27.419607] machzwd: no ZF-Logic found To reproduce: # build kernel cd linux cp config-5.2.0-rc6-01699-g4de83b8 .config make HOSTCC=gcc-7 CC=gcc-7 ARCH=x86_64 olddefconfig prepare modules_prepare bzImage git clone https://github.com/intel/lkp-tests.git cd lkp-tests bin/lkp qemu -k job-script # job-script is attached in this email Thanks, Rong Chen