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Subject[PATCH 14/15] sched, clock: Fixup clear_sched_clock_stable()
The below tells us the static_key conversion has a problem; since the
exact point of clearing that flag isn't too important, delay the flip
and use a workqueue to process it.

[ ] TSC synchronization [CPU#0 -> CPU#22]:
[ ] Measured 8 cycles TSC warp between CPUs, turning off TSC clock.
[ ]
[ ] ======================================================
[ ] [ INFO: possible circular locking dependency detected ]
[ ] 3.13.0-rc3-01745-g848b0d0322cb-dirty #637 Not tainted
[ ] -------------------------------------------------------
[ ] swapper/0/1 is trying to acquire lock:
[ ] (jump_label_mutex){+.+...}, at: [<ffffffff8115a637>] jump_label_lock+0x17/0x20
[ ]
[ ] but task is already holding lock:
[ ] (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8109408b>] cpu_hotplug_begin+0x2b/0x60
[ ]
[ ] which lock already depends on the new lock.
[ ]
[ ]
[ ] the existing dependency chain (in reverse order) is:
[ ]
[ ] -> #1 (cpu_hotplug.lock){+.+.+.}:
[ ] [<ffffffff810def00>] lock_acquire+0x90/0x130
[ ] [<ffffffff81661f83>] mutex_lock_nested+0x63/0x3e0
[ ] [<ffffffff81093fdc>] get_online_cpus+0x3c/0x60
[ ] [<ffffffff8104cc67>] arch_jump_label_transform+0x37/0x130
[ ] [<ffffffff8115a3cf>] __jump_label_update+0x5f/0x80
[ ] [<ffffffff8115a48d>] jump_label_update+0x9d/0xb0
[ ] [<ffffffff8115aa6d>] static_key_slow_inc+0x9d/0xb0
[ ] [<ffffffff810c0f65>] sched_feat_set+0xf5/0x100
[ ] [<ffffffff810c5bdc>] set_numabalancing_state+0x2c/0x30
[ ] [<ffffffff81d12f3d>] numa_policy_init+0x1af/0x1b7
[ ] [<ffffffff81cebdf4>] start_kernel+0x35d/0x41f
[ ] [<ffffffff81ceb5a5>] x86_64_start_reservations+0x2a/0x2c
[ ] [<ffffffff81ceb6a2>] x86_64_start_kernel+0xfb/0xfe
[ ]
[ ] -> #0 (jump_label_mutex){+.+...}:
[ ] [<ffffffff810de141>] __lock_acquire+0x1701/0x1eb0
[ ] [<ffffffff810def00>] lock_acquire+0x90/0x130
[ ] [<ffffffff81661f83>] mutex_lock_nested+0x63/0x3e0
[ ] [<ffffffff8115a637>] jump_label_lock+0x17/0x20
[ ] [<ffffffff8115aa3b>] static_key_slow_inc+0x6b/0xb0
[ ] [<ffffffff810ca775>] clear_sched_clock_stable+0x15/0x20
[ ] [<ffffffff810503b3>] mark_tsc_unstable+0x23/0x70
[ ] [<ffffffff810772cb>] check_tsc_sync_source+0x14b/0x150
[ ] [<ffffffff81076612>] native_cpu_up+0x3a2/0x890
[ ] [<ffffffff810941cb>] _cpu_up+0xdb/0x160
[ ] [<ffffffff810942c9>] cpu_up+0x79/0x90
[ ] [<ffffffff81d0af6b>] smp_init+0x60/0x8c
[ ] [<ffffffff81cebf42>] kernel_init_freeable+0x8c/0x197
[ ] [<ffffffff8164e32e>] kernel_init+0xe/0x130
[ ] [<ffffffff8166beec>] ret_from_fork+0x7c/0xb0
[ ]
[ ] other info that might help us debug this:
[ ]
[ ] Possible unsafe locking scenario:
[ ]
[ ] CPU0 CPU1
[ ] ---- ----
[ ] lock(cpu_hotplug.lock);
[ ] lock(jump_label_mutex);
[ ] lock(cpu_hotplug.lock);
[ ] lock(jump_label_mutex);
[ ]
[ ] *** DEADLOCK ***
[ ]
[ ] 2 locks held by swapper/0/1:
[ ] #0: (cpu_add_remove_lock){+.+.+.}, at: [<ffffffff81094037>] cpu_maps_update_begin+0x17/0x20
[ ] #1: (cpu_hotplug.lock){+.+.+.}, at: [<ffffffff8109408b>] cpu_hotplug_begin+0x2b/0x60
[ ]
[ ] stack backtrace:
[ ] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.13.0-rc3-01745-g848b0d0322cb-dirty #637
[ ] Hardware name: Supermicro X8DTN/X8DTN, BIOS 4.6.3 01/08/2010
[ ] ffffffff82c9c270 ffff880236843bb8 ffffffff8165c5f5 ffffffff82c9c270
[ ] ffff880236843bf8 ffffffff81658c02 ffff880236843c80 ffff8802368586a0
[ ] ffff880236858678 0000000000000001 0000000000000002 ffff880236858000
[ ] Call Trace:
[ ] [<ffffffff8165c5f5>] dump_stack+0x4e/0x7a
[ ] [<ffffffff81658c02>] print_circular_bug+0x1f9/0x207
[ ] [<ffffffff810de141>] __lock_acquire+0x1701/0x1eb0
[ ] [<ffffffff816680ff>] ? __atomic_notifier_call_chain+0x8f/0xb0
[ ] [<ffffffff810def00>] lock_acquire+0x90/0x130
[ ] [<ffffffff8115a637>] ? jump_label_lock+0x17/0x20
[ ] [<ffffffff8115a637>] ? jump_label_lock+0x17/0x20
[ ] [<ffffffff81661f83>] mutex_lock_nested+0x63/0x3e0
[ ] [<ffffffff8115a637>] ? jump_label_lock+0x17/0x20
[ ] [<ffffffff8115a637>] jump_label_lock+0x17/0x20
[ ] [<ffffffff8115aa3b>] static_key_slow_inc+0x6b/0xb0
[ ] [<ffffffff810ca775>] clear_sched_clock_stable+0x15/0x20
[ ] [<ffffffff810503b3>] mark_tsc_unstable+0x23/0x70
[ ] [<ffffffff810772cb>] check_tsc_sync_source+0x14b/0x150
[ ] [<ffffffff81076612>] native_cpu_up+0x3a2/0x890
[ ] [<ffffffff810941cb>] _cpu_up+0xdb/0x160
[ ] [<ffffffff810942c9>] cpu_up+0x79/0x90
[ ] [<ffffffff81d0af6b>] smp_init+0x60/0x8c
[ ] [<ffffffff81cebf42>] kernel_init_freeable+0x8c/0x197
[ ] [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ] [<ffffffff8164e32e>] kernel_init+0xe/0x130
[ ] [<ffffffff8166beec>] ret_from_fork+0x7c/0xb0
[ ] [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ] ------------[ cut here ]------------
[ ] WARNING: CPU: 0 PID: 1 at /usr/src/linux-2.6/kernel/smp.c:374 smp_call_function_many+0xad/0x300()
[ ] Modules linked in:
[ ] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.13.0-rc3-01745-g848b0d0322cb-dirty #637
[ ] Hardware name: Supermicro X8DTN/X8DTN, BIOS 4.6.3 01/08/2010
[ ] 0000000000000009 ffff880236843be0 ffffffff8165c5f5 0000000000000000
[ ] ffff880236843c18 ffffffff81093d8c 0000000000000000 0000000000000000
[ ] ffffffff81ccd1a0 ffffffff810ca951 0000000000000000 ffff880236843c28
[ ] Call Trace:
[ ] [<ffffffff8165c5f5>] dump_stack+0x4e/0x7a
[ ] [<ffffffff81093d8c>] warn_slowpath_common+0x8c/0xc0
[ ] [<ffffffff810ca951>] ? sched_clock_tick+0x1/0xa0
[ ] [<ffffffff81093dda>] warn_slowpath_null+0x1a/0x20
[ ] [<ffffffff8110b72d>] smp_call_function_many+0xad/0x300
[ ] [<ffffffff8104f200>] ? arch_unregister_cpu+0x30/0x30
[ ] [<ffffffff8104f200>] ? arch_unregister_cpu+0x30/0x30
[ ] [<ffffffff810ca951>] ? sched_clock_tick+0x1/0xa0
[ ] [<ffffffff8110ba96>] smp_call_function+0x46/0x80
[ ] [<ffffffff8104f200>] ? arch_unregister_cpu+0x30/0x30
[ ] [<ffffffff8110bb3c>] on_each_cpu+0x3c/0xa0
[ ] [<ffffffff810ca950>] ? sched_clock_idle_sleep_event+0x20/0x20
[ ] [<ffffffff810ca951>] ? sched_clock_tick+0x1/0xa0
[ ] [<ffffffff8104f964>] text_poke_bp+0x64/0xd0
[ ] [<ffffffff810ca950>] ? sched_clock_idle_sleep_event+0x20/0x20
[ ] [<ffffffff8104ccde>] arch_jump_label_transform+0xae/0x130
[ ] [<ffffffff8115a3cf>] __jump_label_update+0x5f/0x80
[ ] [<ffffffff8115a48d>] jump_label_update+0x9d/0xb0
[ ] [<ffffffff8115aa6d>] static_key_slow_inc+0x9d/0xb0
[ ] [<ffffffff810ca775>] clear_sched_clock_stable+0x15/0x20
[ ] [<ffffffff810503b3>] mark_tsc_unstable+0x23/0x70
[ ] [<ffffffff810772cb>] check_tsc_sync_source+0x14b/0x150
[ ] [<ffffffff81076612>] native_cpu_up+0x3a2/0x890
[ ] [<ffffffff810941cb>] _cpu_up+0xdb/0x160
[ ] [<ffffffff810942c9>] cpu_up+0x79/0x90
[ ] [<ffffffff81d0af6b>] smp_init+0x60/0x8c
[ ] [<ffffffff81cebf42>] kernel_init_freeable+0x8c/0x197
[ ] [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ] [<ffffffff8164e32e>] kernel_init+0xe/0x130
[ ] [<ffffffff8166beec>] ret_from_fork+0x7c/0xb0
[ ] [<ffffffff8164e320>] ? rest_init+0xd0/0xd0
[ ] ---[ end trace 6ff1df5620c49d26 ]---
[ ] tsc: Marking TSC unstable due to check_tsc_sync_source failed

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
kernel/sched/clock.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

--- a/kernel/sched/clock.c
+++ b/kernel/sched/clock.c
@@ -59,6 +59,7 @@
#include <linux/ktime.h>
#include <linux/sched.h>
#include <linux/static_key.h>
+#include <linux/workqueue.h>

/*
* Scheduler clock - returns current time in nanosec units.
@@ -90,13 +91,20 @@ void set_sched_clock_stable(void)
static_key_slow_dec(&__sched_clock_stable);
}

-void clear_sched_clock_stable(void)
+static void __clear_sched_clock_stable(struct work_struct *work)
{
/* XXX worry about clock continuity */
if (sched_clock_stable())
static_key_slow_inc(&__sched_clock_stable);
}

+static DECLARE_WORK(sched_clock_work, __clear_sched_clock_stable);
+
+void clear_sched_clock_stable(void)
+{
+ schedule_work(&sched_clock_work);
+}
+
struct sched_clock_data {
u64 tick_raw;
u64 tick_gtod;



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