ledtrig-cpu: kill useless mutex to fix sleep in atomic context

Seeing the following every time the CPU enters or leaves idle on a
Beagleboard:

BUG: sleeping function called from invalid context at kernel/mutex.c:269
in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0
no locks held by swapper/0/0.
[<c001659c>] (unwind_backtrace+0x0/0xf8) from [<c05aaa7c>] (mutex_lock_nested+0x24/0x380)
[<c05aaa7c>] (mutex_lock_nested+0x24/0x380) from [<c043bd1c>] (ledtrig_cpu+0x38/0x88)
[<c043bd1c>] (ledtrig_cpu+0x38/0x88) from [<c000f4b0>] (cpu_idle+0xf4/0x120)
[<c000f4b0>] (cpu_idle+0xf4/0x120) from [<c07e47c8>] (start_kernel+0x2bc/0x30c)

Miles Lane has reported seeing similar splats during system suspend.

The mutex in struct led_trigger_cpu appears to have no function: it
resides in a per-cpu data structure which never changes after the
trigger is registered. So just remove it.

Reported-by: Miles Lane <[e-mail]>
Signed-off-by: Nathan Lynch <[e-mail]>
Signed-off-by: Bryan Wu <roc@roc-samos.(none)>

drivers/leds/ledtrig-cpu.c

···
 struct led_trigger_cpu {
 	char name[MAX_NAME_LEN];
 	struct led_trigger *_trig;
-	struct mutex lock;
-	int lock_is_inited;
 };
 
 static DEFINE_PER_CPU(struct led_trigger_cpu, cpu_trig);
···
 void ledtrig_cpu(enum cpu_led_event ledevt)
 {
 	struct led_trigger_cpu *trig = &__get_cpu_var(cpu_trig);
-
-	/* mutex lock should be initialized before calling mutex_call() */
-	if (!trig->lock_is_inited)
-		return;
-
-	mutex_lock(&trig->lock);
 
 	/* Locate the correct CPU LED */
 	switch (ledevt) {
···
 		/* Will leave the LED as it is */
 		break;
 	}
-
-	mutex_unlock(&trig->lock);
 }
 EXPORT_SYMBOL(ledtrig_cpu);
 
···
 	for_each_possible_cpu(cpu) {
 		struct led_trigger_cpu *trig = &per_cpu(cpu_trig, cpu);
 
-		mutex_init(&trig->lock);
-
 		snprintf(trig->name, MAX_NAME_LEN, "cpu%d", cpu);
 
-		mutex_lock(&trig->lock);
 		led_trigger_register_simple(trig->name, &trig->_trig);
-		trig->lock_is_inited = 1;
-		mutex_unlock(&trig->lock);
 	}
 
 	register_syscore_ops(&ledtrig_cpu_syscore_ops);
···
 	for_each_possible_cpu(cpu) {
 		struct led_trigger_cpu *trig = &per_cpu(cpu_trig, cpu);
 
-		mutex_lock(&trig->lock);
-
 		led_trigger_unregister_simple(trig->_trig);
 		trig->_trig = NULL;
 		memset(trig->name, 0, MAX_NAME_LEN);
-		trig->lock_is_inited = 0;
-
-		mutex_unlock(&trig->lock);
-		mutex_destroy(&trig->lock);
 	}
 
 	unregister_syscore_ops(&ledtrig_cpu_syscore_ops);