The following call trace is observed in preempt_rt:
------
BUG: sleeping function called from invalid context at
/opt/platforms/atom_prj/build/linux/kernel/rtmutex.c:707
pcnt: 0 0 in_atomic(): 0, irqs_disabled(): 1, pid: 5928, name: kstop/1
Pid: 5928, comm: kstop/1 Tainted: P 2.6.38.6-rt_preempt_rt #1
Call Trace:
[<c102d101>] __might_sleep+0xe1/0x100
[<c15a6cb7>] rt_spin_lock+0x27/0x70
[<c159e4e7>] hotcpu_callback+0x13/0x102
[<c1060155>] notifier_call_chain+0x35/0x70
[<c106023a>] raw_notifier_call_chain+0x1a/0x20
[<c15969ff>] take_cpu_down+0x2f/0x60
[<c107ef25>] stop_cpu+0x95/0xd0
[<c1056550>] worker_thread+0x110/0x230
[<c15a4f9b>] ? __schedule+0x22b/0x6c0
[<c106ccd2>] ? rt_mutex_adjust_prio+0x32/0x50
[<c107ee90>] ? stop_cpu+0x0/0xd0
[<c105aa30>] ? autoremove_wake_function+0x0/0x40
[<c1056440>] ? worker_thread+0x0/0x230
[<c105a71c>] kthread+0x6c/0x80
[<c105a6b0>] ? kthread+0x0/0x80
[<c1003336>] kernel_thread_helper+0x6/0x30
CPU 1 is now offline
------
To track it as follows:
------
stop_cpu()
local_irq_disable()
take_cpu_down()
raw_notifier_call_chain() <-- CPU_DYING
|
+ hotcpu_callback()
{
spin_lock(&async_tsc_lock);
......
spin_unlock(&async_tsc_lock);
}
------
Since spin_lock is actually rt_spin_lock under preempt_rt, a call trace
will be issued when it's trying to hold async_tsc_lock when interrupts
are disabled.
The fix is to move async_tsc_lock into switch cases, allow the CPU_DYING
handling fall through without holding the spin lock.
Signed-off-by: Ming Liu <[email protected]>
---
arch/x86/kernel/trace-clock.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/trace-clock.c b/arch/x86/kernel/trace-clock.c
index 47539e2..a7a51ce 100644
--- a/arch/x86/kernel/trace-clock.c
+++ b/arch/x86/kernel/trace-clock.c
@@ -145,7 +145,6 @@ static int __cpuinit hotcpu_callback(struct notifier_block
*nb,
unsigned int hotcpu = (unsigned long)hcpu;
int cpu;
- spin_lock(&async_tsc_lock);
switch (action) {
case CPU_UP_PREPARE:
case CPU_UP_PREPARE_FROZEN:
@@ -159,6 +158,7 @@ static int __cpuinit hotcpu_callback(struct notifier_block
*nb,
* the CPU_ONLINE notification. It's just there to give a
* maximum bound to the TSC error.
*/
+ spin_lock(&async_tsc_lock);
if (async_tsc_refcount && !trace_clock_is_sync()) {
if (!async_tsc_enabled) {
async_tsc_enabled = 1;
@@ -168,12 +168,15 @@ static int __cpuinit hotcpu_callback(struct
notifier_block *nb,
enable_trace_clock(hotcpu);
}
}
+ spin_unlock(&async_tsc_lock);
break;
#ifdef CONFIG_HOTPLUG_CPU
case CPU_UP_CANCELED:
case CPU_UP_CANCELED_FROZEN:
+ spin_lock(&async_tsc_lock);
if (!async_tsc_refcount && num_online_cpus() == 1)
set_trace_clock_is_sync(1);
+ spin_unlock(&async_tsc_lock);
break;
case CPU_DEAD:
case CPU_DEAD_FROZEN:
@@ -182,14 +185,15 @@ static int __cpuinit hotcpu_callback(struct
notifier_block *nb,
* active even if we go back to a synchronized state (1 CPU)
* because the CPU left could be the one lagging behind.
*/
+ spin_lock(&async_tsc_lock);
if (async_tsc_refcount && async_tsc_enabled)
disable_trace_clock(hotcpu);
if (!async_tsc_refcount && num_online_cpus() == 1)
set_trace_clock_is_sync(1);
+ spin_unlock(&async_tsc_lock);
break;
#endif /* CONFIG_HOTPLUG_CPU */
}
- spin_unlock(&async_tsc_lock);
return NOTIFY_OK;
}
--
1.8.4.1
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