Hi!
From: Srinivas Pandruvada srinivas.pandruvada@linux.intel.com
[ Upstream commit 68b99e94a4a2db6ba9b31fe0485e057b9354a640 ]
When CPU 0 is offline and intel_powerclamp is used to inject idle, it generates kernel BUG:
BUG: using smp_processor_id() in preemptible [00000000] code: bash/15687 caller is debug_smp_processor_id+0x17/0x20 CPU: 4 PID: 15687 Comm: bash Not tainted 5.19.0-rc7+ #57 Call Trace:
<TASK> dump_stack_lvl+0x49/0x63 dump_stack+0x10/0x16 check_preemption_disabled+0xdd/0xe0 debug_smp_processor_id+0x17/0x20 powerclamp_set_cur_state+0x7f/0xf9 [intel_powerclamp] ... ...
Here CPU 0 is the control CPU by default and changed to the current CPU, if CPU 0 offlined. This check has to be performed under cpus_read_lock(), hence the above warning.
Use get_cpu() instead of smp_processor_id() to avoid this BUG.
This has exactly the same problem as smp_processor_id(), you just worked around the warning. If it is okay that control_cpu contains stale value, could we have a comment explaining why?
Thanks, Pavel
+++ b/drivers/thermal/intel_powerclamp.c @@ -519,8 +519,10 @@ static int start_power_clamp(void) /* prefer BSP */ control_cpu = 0;
- if (!cpu_online(control_cpu))
control_cpu = smp_processor_id();
- if (!cpu_online(control_cpu)) {
control_cpu = get_cpu();put_cpu();- }
clamping = true; schedule_delayed_work(&poll_pkg_cstate_work, 0); -- 2.35.1