thermal/powerclamp: Prevent division by zero when counting interval

I have got a zero division error when disabling the forced
idle injection from the intel powerclamp. I did

  echo 0 >/sys/class/thermal/cooling_device48/cur_state

and got

[  986.072632] divide error: 0000 [#1] PREEMPT SMP
[  986.078989] Modules linked in:
[  986.083618] CPU: 17 PID: 24967 Comm: kidle_inject/17 Not tainted 4.7.0-1-default+ #3055
[  986.093781] Hardware name: Intel Corporation S2600CP/S2600CP, BIOS RMLSDP.86I.R3.27.D685.1305151734 05/15/2013
[  986.106227] task: ffff880430e1c080 task.stack: ffff880427ef0000
[  986.114122] RIP: 0010:[<ffffffff81794859>]  [<ffffffff81794859>] clamp_thread+0x1d9/0x600
[  986.124609] RSP: 0018:ffff880427ef3e20  EFLAGS: 00010246
[  986.131860] RAX: 0000000000000258 RBX: 0000000000000006 RCX: 0000000000000001
[  986.141179] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000018
[  986.150478] RBP: ffff880427ef3ec8 R08: ffff880427ef0000 R09: 0000000000000002
[  986.159779] R10: 0000000000003df2 R11: 0000000000000018 R12: 0000000000000002
[  986.169089] R13: 0000000000000000 R14: ffff880427ef0000 R15: ffff880427ef0000
[  986.178388] FS:  0000000000000000(0000) GS:ffff880435940000(0000) knlGS:0000000000000000
[  986.188785] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  986.196559] CR2: 00007f1d0caf0000 CR3: 0000000002006000 CR4: 00000000001406e0
[  986.205909] Stack:
[  986.209524]  ffff8802be897b00 ffff880430e1c080 0000000000000011 0000006a35959780
[  986.219236]  0000000000000011 ffff880427ef0008 0000000000000000 ffff8804359503d0
[  986.228966]  0000000100029d93 ffffffff81794140 0000000000000000 ffffffff05000011
[  986.238686] Call Trace:
[  986.242825]  [<ffffffff81794140>] ? pkg_state_counter+0x80/0x80
[  986.250866]  [<ffffffff81794680>] ? powerclamp_set_cur_state+0x180/0x180
[  986.259797]  [<ffffffff8111d1a9>] kthread+0xc9/0xe0
[  986.266682]  [<ffffffff8193d69f>] ret_from_fork+0x1f/0x40
[  986.274142]  [<ffffffff8111d0e0>] ? kthread_create_on_node+0x180/0x180
[  986.282869] Code: d1 ea 48 89 d6 80 3d 6a d0 d4 00 00 ba 64 00 00 00 89 d8 41 0f 45 f5 0f af c2 42 8d 14 2e be 31 00 00 00 83 fa 31 0f 42 f2 31 d2 <f7> f6 48 8b 15 9e 07 87 00 48 8b 3d 97 07 87 00 48 63 f0 83 e8
[  986.307806] RIP  [<ffffffff81794859>] clamp_thread+0x1d9/0x600
[  986.315871]  RSP <ffff880427ef3e20>

RIP points to the following lines:

	compensation = get_compensation(target_ratio);
	interval = duration_jiffies*100/(target_ratio+compensation);

A solution would be to switch the following two commands in
powerclamp_set_cur_state():

	set_target_ratio = 0;
	end_power_clamp();

But I think that the zero division might happen also when target_ratio
is non-zero because the compensation might be negative. Therefore
we also check the sum of target_ratio and compensation explicitly.

Also the compensated_ratio variable is always set. Therefore there
is no need to initialize it.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>

drivers/thermal/intel_powerclamp.c

@@ -388,7 +388,7 @@ static int clamp_thread(void *arg)
 		int sleeptime;
 		unsigned long target_jiffies;
 		unsigned int guard;
-		unsigned int compensation = 0;
+		unsigned int compensated_ratio;
 		int interval; /* jiffies to sleep for each attempt */
 		unsigned int duration_jiffies = msecs_to_jiffies(duration);
 		unsigned int window_size_now;
@@ -409,8 +409,11 @@ static int clamp_thread(void *arg)
 		 * c-states, thus we need to compensate the injected idle ratio
 		 * to achieve the actual target reported by the HW.
 		 */
-		compensation = get_compensation(target_ratio);
-		interval = duration_jiffies*100/(target_ratio+compensation);
+		compensated_ratio = target_ratio +
+			get_compensation(target_ratio);
+		if (compensated_ratio <= 0)
+			compensated_ratio = 1;
+		interval = duration_jiffies * 100 / compensated_ratio;
 
 		/* align idle time */
 		target_jiffies = roundup(jiffies, interval);
@@ -647,8 +650,8 @@ static int powerclamp_set_cur_state(struct thermal_cooling_device *cdev,
 		goto exit_set;
 	} else	if (set_target_ratio > 0 && new_target_ratio == 0) {
 		pr_info("Stop forced idle injection\n");
-		set_target_ratio = 0;
 		end_power_clamp();
+		set_target_ratio = 0;
 	} else	/* adjust currently running */ {
 		set_target_ratio = new_target_ratio;
 		/* make new set_target_ratio visible to other cpus */