Greetings, I got the below dmesg and the first bad commit is commit 6acce3ef84520537f8a09a12c9ddbe814a584dd2 Author: Peter Zijlstra Date: Fri Oct 11 14:38:20 2013 +0200 sched: Remove get_online_cpus() usage Remove get_online_cpus() usage from the scheduler; there's 4 sites that use it: - sched_init_smp(); where its completely superfluous since we're in 'early' boot and there simply cannot be any hotplugging. - sched_getaffinity(); we already take a raw spinlock to protect the task cpus_allowed mask, this disables preemption and therefore also stabilizes cpu_online_mask as that's modified using stop_machine. However switch to active mask for symmetry with sched_setaffinity()/set_cpus_allowed_ptr(). We guarantee active mask stability by inserting sync_rcu/sched() into _cpu_down. - sched_setaffinity(); we don't appear to need get_online_cpus() either, there's two sites where hotplug appears relevant: * cpuset_cpus_allowed(); for the !cpuset case we use possible_mask, for the cpuset case we hold task_lock, which is a spinlock and thus for mainline disables preemption (might cause pain on RT). * set_cpus_allowed_ptr(); Holds all scheduler locks and thus has preemption properly disabled; also it already deals with hotplug races explicitly where it releases them. - migrate_swap(); we can make stop_two_cpus() do the heavy lifting for us with a little trickery. By adding a sync_sched/rcu() after the CPU_DOWN_PREPARE notifier we can provide preempt/rcu guarantees for cpu_active_mask. Use these to validate that both our cpus are active when queueing the stop work before we queue the stop_machine works for take_cpu_down(). Signed-off-by: Peter Zijlstra Cc: "Srivatsa S. Bhat" Cc: Paul McKenney Cc: Mel Gorman Cc: Rik van Riel Cc: Srikar Dronamraju Cc: Andrea Arcangeli Cc: Johannes Weiner Cc: Linus Torvalds Cc: Andrew Morton Cc: Steven Rostedt Cc: Oleg Nesterov Link: http://lkml.kernel.org/r/20131011123820.GV3081@twins.programming.kicks-ass.net Signed-off-by: Ingo Molnar [3165] Watchdog is alive [3159] Started watchdog thread 3165 [ 58.695502] ------------[ cut here ]------------ [ 58.697835] WARNING: CPU: 0 PID: 3166 at kernel/cpu.c:84 put_online_cpus+0x43/0x70() [ 58.702423] Modules linked in: [ 58.704404] CPU: 0 PID: 3166 Comm: trinity-child0 Not tainted 3.12.0-rc5-01882-gf3db366 #1172 [ 58.708530] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 58.710992] 0000000000000000 ffff88000acfbe50 ffffffff81a24643 0000000000000000 [ 58.715410] ffff88000acfbe88 ffffffff810c3e6b ffffffff810c3fef 0000000000000000 [ 58.719826] 0000000000000000 0000000000006ee0 0000000000000ffc ffff88000acfbe98 [ 58.724348] Call Trace: [ 58.726190] [] dump_stack+0x4d/0x66 [ 58.728531] [] warn_slowpath_common+0x7f/0x98 [ 58.731069] [] ? put_online_cpus+0x43/0x70 [ 58.733664] [] warn_slowpath_null+0x1a/0x1c [ 58.736258] [] put_online_cpus+0x43/0x70 [ 58.738686] [] sched_setaffinity+0x7d/0x1f9 [ 58.741210] [] ? sched_setaffinity+0x5/0x1f9 [ 58.743775] [] ? _raw_spin_unlock_irq+0x2c/0x3e [ 58.746417] [] ? do_setitimer+0x194/0x1f5 [ 58.748899] [] SyS_sched_setaffinity+0x62/0x71 [ 58.751481] [] system_call_fastpath+0x16/0x1b [ 58.754070] ---[ end trace 034818a1f6f06868 ]--- [ 58.757521] ------------[ cut here ]------------ git bisect start f3db36699379159b761cdbc093347822a633c616 2fe80d3bbf1c8bd9efc5b8154207c8dd104e7306 -- git bisect good 0f2a02d75d0f37f1624585c50c3250b6d096f050 # 12:02 21+ 19 kvm tools: fix function name git bisect good ee6946e6810792f208662507055e6f9c32f42898 # 13:47 21+ 0 x86: perf -- Allow perf watchdog to use perfmon bit for msr index computation git bisect good 2eb3090631e1f3c5920e27e0a51ed876e88fe871 # 15:07 21+ 0 Merge branch 'linus' git bisect good bf2575c121ca11247ef07fd02b43f7430834f7b1 # 15:58 21+ 0 perf trace: Add summary option to dump syscall statistics git bisect good d6099aeb4a9aad5e7ab1c72eb119ebd52dee0d52 # 16:36 21+ 0 Merge branch 'fixes' of git://git.linaro.org/people/rmk/linux-arm git bisect good 54d54a7146ce2718738f97374d714dd6f5e103b0 # 16:56 21+ 0 Merge branch 'x86/urgent' git bisect good ed8ada393388ef7ccfcfb3a88d8718f7df4b3165 # 17:44 21+ 0 Merge tag 'rdma-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/roland/infiniband git bisect good f773934fb39d11608b8285db621ae65ca1465bf3 # 18:09 21+ 0 Merge branch 'perf/core' git bisect bad c2d816443ef305aba8eaf0bf368f4d3d87494f06 # 18:09 0- 9 sched/wait: Introduce prepare_to_wait_event() git bisect good 746023159c40c523b08a3bc3d213dac212385895 # 18:45 21+ 1 sched: Fix race in migrate_swap_stop() git bisect bad 8922915b38cd8b72f8e5af614b95be71d1d299d4 # 19:00 0- 1 sched/wait: Add ___wait_cond_timeout() to wait_event*_timeout() too git bisect bad 6acce3ef84520537f8a09a12c9ddbe814a584dd2 # 19:13 0- 1 sched: Remove get_online_cpus() usage git bisect good 746023159c40c523b08a3bc3d213dac212385895 # 20:01 63+ 3 sched: Fix race in migrate_swap_stop() git bisect bad f3db36699379159b761cdbc093347822a633c616 # 20:01 0- 16 Merge branch 'sched/core' git bisect good 8df5f2f7724ba6566e92c87cf2354735aac4b9ed # 20:53 63+ 11 Revert "sched: Remove get_online_cpus() usage" git bisect good 04919afb85c8f007b7326c4da5eb61c52e91b9c7 # 21:36 63+ 3 Merge branch 'for-linus' of git://git.samba.org/sfrench/cifs-2.6 git bisect good a0cf1abc25ac197dd97b857c0f6341066a8cb1cf # 22:29 63+ 6 Add linux-next specific files for 20130927 git bisect bad 574c653ee9062a8fcc619e7ec83a36ba2dfc5a26 # 22:43 0- 2 Merge branch 'core/rcu' Thanks, Fengguang