On Thu, Mar 09, 2017 at 10:37:32AM -0800, Paul E. McKenney wrote: > On Thu, Mar 09, 2017 at 07:31:14AM -0800, Paul E. McKenney wrote: > > On Thu, Mar 09, 2017 at 04:24:20PM +0100, Peter Zijlstra wrote: > > > On Wed, Mar 08, 2017 at 01:53:06PM -0800, Paul E. McKenney wrote: > > > > The v4.11-rc1 kernel emits the following splat in some configurations: > > > > > > > > [ 43.681891] BUG: using smp_processor_id() in preemptible [00000000] > > > > code: kworker/3:1/49 > > > > [ 43.682511] caller is debug_smp_processor_id+0x17/0x20 > > > > [ 43.682893] CPU: 0 PID: 49 Comm: kworker/3:1 Not tainted 4.11.0-rc1+ > > > > #1 > > > > [ 43.683382] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), > > > > BIOS Bochs 01/01/2011 > > > > [ 43.683497] Workqueue: events __clear_sched_clock_stable > > > > [ 43.683497] Call Trace: > > > > [ 43.683497] dump_stack+0x4f/0x69 > > > > [ 43.683497] check_preemption_disabled+0xd9/0xf0 > > > > [ 43.683497] debug_smp_processor_id+0x17/0x20 > > > > [ 43.683497] __clear_sched_clock_stable+0x11/0x60 > > > > [ 43.683497] process_one_work+0x146/0x430 > > > > [ 43.683497] worker_thread+0x126/0x490 > > > > [ 43.683497] kthread+0xfc/0x130 > > > > [ 43.683497] ? process_one_work+0x430/0x430 > > > > [ 43.683497] ? kthread_create_on_node+0x40/0x40 > > > > [ 43.683497] ? umh_complete+0x30/0x30 > > > > [ 43.683497] ? call_usermodehelper_exec_async+0x12a/0x130 > > > > [ 43.683497] ret_from_fork+0x29/0x40 > > > > [ 43.689244] sched_clock: Marking unstable (43688244724, > > > > 179505618)<-(43867750342, 0) > > > > > > > > This happens because workqueue handlers run with preemption enabled > > > > by default and the new this_scd() function accesses per-CPU variables. > > > > This commit therefore disables preemption across this call to this_scd() > > > > and to the uses of the pointer that it returns. Lightly tested > > > > successfully on x86. > > > > > > Does this also work? > > > > Thank you! I will give it a shot after the other tests complete. > > And it does pass light testing. I will hammer it harder this evening. > > So please send a formal patch!
And the diffs below passed overnight testing, so: Tested-by: Paul E. McKenney <[email protected]> ------------------------------------------------------------------------ commit e87df240b9e6a24635a1c8674f715554f27df6cc Author: Paul E. McKenney <[email protected]> Date: Thu Mar 9 07:51:25 2017 -0800 EXPERIMENTAL: Peter Zijlstra hotplug fix Not-signed-off-by: Paul E. McKenney <[email protected]> diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c index a08795e21628..1560d5f961ef 100644 --- a/kernel/sched/clock.c +++ b/kernel/sched/clock.c @@ -172,8 +172,8 @@ void clear_sched_clock_stable(void) smp_mb(); /* matches sched_clock_init_late() */ - if (sched_clock_running == 2) - schedule_work(&sched_clock_work); + if (sched_clock_running == 2 && sched_clock_stable()) + schedule_work_on(smp_processor_id(), &sched_clock_work); } void sched_clock_init_late(void)
