[PATCH v2] thermal/powerclamp: Prevent division by zero when counting interval
From: Petr Mladek
Date: Fri Aug 05 2016 - 09:21:28 EST
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@xxxxxxxx>
---
Changes against v1:
+ Also set_target_ratio to 0 after the threads are stopped.
drivers/thermal/intel_powerclamp.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/drivers/thermal/intel_powerclamp.c b/drivers/thermal/intel_powerclamp.c
index 015ce2eb6eb7..0e4dc0afcfd2 100644
--- a/drivers/thermal/intel_powerclamp.c
+++ b/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 */
--
1.8.5.6