linux-kernel - [PATCH] thermal/drivers/intel_powerclamp: Fix bug for smp_processor

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Message-Id: <20220920110657.1948320-1-srinivas.pandruvada@linux.intel.com>
Date:   Tue, 20 Sep 2022 04:06:57 -0700
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     rafael@...nel.org, rui.zhang@...el.com, daniel.lezcano@...aro.org
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Chen Yu <yu.c.chen@...el.com>
Subject: [PATCH] thermal/drivers/intel_powerclamp: Fix bug for smp_processor_id

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.

Suggested-by: Chen Yu <yu.c.chen@...el.com>
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
---
 drivers/thermal/intel/intel_powerclamp.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/thermal/intel/intel_powerclamp.c b/drivers/thermal/intel/intel_powerclamp.c
index c841ab37e7c6..46cd799af148 100644
--- a/drivers/thermal/intel/intel_powerclamp.c
+++ b/drivers/thermal/intel/intel_powerclamp.c
@@ -532,8 +532,10 @@ 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);
-- 
2.17.1