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.
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Frederic Weisbecker <fweis...@gmail.com>
diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
index a08795e21628..aa184bea1344 100644
--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -143,7 +143,7 @@ static void __set_sched_clock_stable(void)
static void __clear_sched_clock_stable(struct work_struct *work)
{
- struct sched_clock_data *scd = this_scd();
+ struct sched_clock_data *scd;
/*
* Attempt to make the stable->unstable transition continuous.
@@ -154,7 +154,10 @@ static void __clear_sched_clock_stable(struct work_struct
*work)
*
* Still do what we can.
*/
+ preempt_disable();
+ scd = this_scd();
gtod_offset = (scd->tick_raw + raw_offset) - (scd->tick_gtod);
+ preempt_enable();
printk(KERN_INFO "sched_clock: Marking unstable (%lld, %lld)<-(%lld,
%lld)\n",
scd->tick_gtod, gtod_offset,
