Hi! > From: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx> > > [ 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 -- People of Russia, stop Putin before his war on Ukraine escalates.
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