Greetings, I got the below dmesg and the first bad commit is commit 911af505ef407c2511106c224dd640f882f0f590 Author: Paul E. McKenney Date: Mon Feb 11 10:23:27 2013 -0800 rcu: Provide compile-time control for no-CBs CPUs Currently, the only way to specify no-CBs CPUs is via the rcu_nocbs kernel command-line parameter. This is inconvenient in some cases, particularly for randconfig testing, so this commit adds a new set of kernel configuration parameters. CONFIG_RCU_NOCB_CPU_NONE (the default) retains the old behavior, CONFIG_RCU_NOCB_CPU_ZERO offloads callback processing from CPU 0 (along with any other CPUs specified by the rcu_nocbs boot-time parameter), and CONFIG_RCU_NOCB_CPU_ALL offloads callback processing from all CPUs. Signed-off-by: Paul E. McKenney Signed-off-by: Paul E. McKenney However I guess it's a wrong bisect, the commit should be unmasking an old bug because it merely provides more kconfig options. This warning happened only once in 74 boots of the kernel. I also attached the 2nd dmesg which shows boot hang for the same kernel. Note that there are also 2 kernel hangs in the 74 boots. It should not be an RCU problem, however for completeness, I also attach a dmesg for your reference when considering this RCU warning. [ 33.965802] [sched_delayed] sched: RT throttling activated [ 72.137331] ------------[ cut here ]------------ [ 72.138849] WARNING: at /c/kernel-tests/src/tip/kernel/rcutorture.c:1243 rcu_torture_printk.constprop.12+0x33e/0x4ee() [ 72.154837] CPU: 0 PID: 45 Comm: rcu_torture_sta Not tainted 3.10.0-rc3-03071-gf43e7a3 #16 [ 72.174776] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007 [ 72.176561] ffffffff81b1fd19 ffff880006c41cb8 ffffffff81682d33 ffff880006c41cf8 [ 72.183113] ffffffff810c786e ffff880006c41d18 0000000000000000 00000000000000ca [ 72.199701] 0000000000000001 ffffffff8114cebe 0000000000000000 ffff880006c41d08 [ 72.216691] Call Trace: [ 72.220868] [] dump_stack+0x27/0x30 [ 72.229095] [] warn_slowpath_common+0x80/0xb0 [ 72.245097] [] ? rcu_torture_shutdown+0x15c/0x15c [ 72.247116] [] warn_slowpath_null+0x23/0x2c [ 72.257065] [] rcu_torture_printk.constprop.12+0x33e/0x4ee [ 72.267641] [] rcu_torture_stats_print+0x10/0x35 [ 72.276533] [] rcu_torture_stats+0x55/0xb8 [ 72.288540] [] kthread+0x113/0x122 [ 72.290221] [] ? __schedule+0xe4/0xaf8 [ 72.319276] [] ? __kthread_parkme+0x91/0x91 [ 72.321293] [] ret_from_fork+0x7c/0xb0 [ 72.333161] [] ? __kthread_parkme+0x91/0x91 [ 72.356133] ---[ end trace 078d362d19f1dfc1 ]--- git bisect start f43e7a34255a387930bc2bb826ec17c052ce975e f8c6512a0cdee9098c807b3ca4480f372de95583 -- git bisect bad 251df49db3327c64bf917bfdba94491fde2b4ee0 # 140 2013-06-07 11:24:55 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input git bisect good 507ffe4f3840ac24890a8123c702cf1b7fe4d33c # 476 2013-06-07 11:53:22 Merge tag 'tty-3.10-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty git bisect bad e486b4c4ba601410772136ba0f8337bf545dccad # 19 2013-06-07 11:58:29 Merge branch 'x86-asm-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip git bisect good 87e7d520edba936fe6d1102e9fcc7530a478c07c # 476 2013-06-07 12:20:43 rtc: rtc-bfin: use devm_*() functions git bisect good 46d9be3e5eb01f71fc02653755d970247174b400 # 476 2013-06-07 12:50:45 Merge branch 'for-3.10' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq git bisect bad e0972916e8fe943f342b0dd1c9d43dbf5bc261c2 # 89 2013-06-07 13:00:48 Merge branch 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip git bisect bad 1f889ec62c3f0d8913f3c32f9aff2a1e15099346 # 6 2013-06-07 13:08:01 Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip git bisect good 8d564368a9a3197f43e56dadf4a18c5738849f94 # 900 2013-06-07 13:51:27 net: rename random32 to prandom git bisect good e57d5cf2f894e3f2727f8cf74bed0bc81cae70c8 # 900 2013-06-07 15:28:21 devcg: remove parent_cgroup. git bisect bad 910ee45db2f4837c8440e770474758493ab94bf7 # 10 2013-06-07 15:34:32 rcu: Make rcu_accelerate_cbs() note need for future grace periods git bisect bad 5e44ce35a6ec1a16522fa2099dda27aefd8a584e # 74 2013-06-07 15:47:33 rcu: Export RCU_FAST_NO_HZ parameters to sysfs git bisect bad dae6e64d2bcfd4b06304ab864c7e3a4f6b5fedf4 # 11 2013-06-07 15:56:02 rcu: Introduce proper blocking to no-CBs kthreads GP waits git bisect bad 911af505ef407c2511106c224dd640f882f0f590 # 65 2013-06-07 16:14:41 rcu: Provide compile-time control for no-CBs CPUs git bisect good 34ed62461ae4970695974afb9a60ac3df0086830 # 900 2013-06-08 04:57:34 rcu: Remove restrictions on no-CBs CPUs git bisect good 34ed62461ae4970695974afb9a60ac3df0086830 # 2700 2013-06-10 14:33:56 rcu: Remove restrictions on no-CBs CPUs git bisect bad f43e7a34255a387930bc2bb826ec17c052ce975e # 14:34 0 Merge branch 'for-next' git bisect bad c04efed734409f5a44715b54a6ca1b54b0ccf215 # 14:41 11 Add linux-next specific files for 20130607 Thanks, Fengguang