[PATCH 5/5] tracing/hwlat: Fix deadlock in cpuhp processing

Another "hung task" error was reported during the test, and i figured out
the deadlock scenario is as follows:

T1 [BP]               | T2 [AP]                     | T3 [hwlatd/1]                  | T4
work_for_cpu_fn()     | cpuhp_thread_fun()          | kthread_fn()                   | hwlat_hotplug_workfn()
  _cpu_down()         |   stop_cpu_kthread()        |                                |   mutex_lock(&hwlat_data.lock)
    cpus_write_lock() |     kthread_stop(hwlatd/1)  |   mutex_lock(&hwlat_data.lock) |
    __cpuhp_kick_ap() |       wait_for_completion() |                                |   cpus_read_lock()

It constitutes ABBA deadlock indirectly between "cpu_hotplug_lock" and
"hwlat_data.lock", make the mutex obtaining in kthread_fn() interruptible
to fix this.

Fixes: ba998f7d9531 ("trace/hwlat: Support hotplug operations")
Signed-off-by: Wei Li <redacted>
---
 kernel/trace/trace_hwlat.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace_hwlat.c b/kernel/trace/trace_hwlat.c
index 3bd6071441ad..4c228ccb8a38 100644
--- a/kernel/trace/trace_hwlat.c
+++ b/kernel/trace/trace_hwlat.c

@@ -370,7 +370,8 @@ static int kthread_fn(void *data)
 		get_sample();
 		local_irq_enable();
 
-		mutex_lock(&hwlat_data.lock);
+		if (mutex_lock_interruptible(&hwlat_data.lock))
+			break;
 		interval = hwlat_data.sample_window - hwlat_data.sample_width;
 		mutex_unlock(&hwlat_data.lock);
 

-- 
2.25.1