linux-kernel - [PATCH] cpufreq, powernow-k8: Fix usage of smp_processor

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Message-ID: <20121009193844.GC7724@alberich>
Date:	Tue, 9 Oct 2012 21:38:44 +0200
From:	Andreas Herrmann <andreas.herrmann3@....com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	<linux-kernel@...r.kernel.org>, <cpufreq@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>, <stable@...r.kernel.org>
Subject: [PATCH] cpufreq, powernow-k8: Fix usage of smp_processor_id() in
 preemptible code


Commit 6889125b8b4e09c5e53e6ecab3433bed1ce198c9
(cpufreq/powernow-k8: workqueue user shouldn't migrate the kworker to another CPU)
causes powernow-k8 to trigger a preempt warning, e.g.:

  BUG: using smp_processor_id() in preemptible [00000000] code: cpufreq/3776
  caller is powernowk8_target+0x20/0x49
  Pid: 3776, comm: cpufreq Not tainted 3.6.0 #9
  Call Trace:
   [<ffffffff8125b447>] debug_smp_processor_id+0xc7/0xe0
   [<ffffffff814877e7>] powernowk8_target+0x20/0x49
   [<ffffffff81482b02>] __cpufreq_driver_target+0x82/0x8a
   [<ffffffff81484fc6>] cpufreq_governor_performance+0x4e/0x54
   [<ffffffff81482c50>] __cpufreq_governor+0x8c/0xc9
   [<ffffffff81482e6f>] __cpufreq_set_policy+0x1a9/0x21e
   [<ffffffff814839af>] store_scaling_governor+0x16f/0x19b
   [<ffffffff81484f16>] ? cpufreq_update_policy+0x124/0x124
   [<ffffffff8162b4a5>] ? _raw_spin_unlock_irqrestore+0x2c/0x49
   [<ffffffff81483640>] store+0x60/0x88
   [<ffffffff811708c0>] sysfs_write_file+0xf4/0x130
   [<ffffffff8111243b>] vfs_write+0xb5/0x151
   [<ffffffff811126e0>] sys_write+0x4a/0x71
   [<ffffffff816319a9>] system_call_fastpath+0x16/0x1b

Fix this by using get_cpu/put_cpu in powernowk8_target().

Cc: Tejun Heo <tj@...nel.org>
Cc: stable@...r.kernel.org
Signed-off-by: Andreas Herrmann <andreas.herrmann3@....com>
---
 drivers/cpufreq/powernow-k8.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/drivers/cpufreq/powernow-k8.c b/drivers/cpufreq/powernow-k8.c
index 1a40935..3d1df2a 100644
--- a/drivers/cpufreq/powernow-k8.c
+++ b/drivers/cpufreq/powernow-k8.c
@@ -1220,17 +1220,20 @@ static long powernowk8_target_fn(void *arg)
 static int powernowk8_target(struct cpufreq_policy *pol,
 		unsigned targfreq, unsigned relation)
 {
+	int this_cpu, ret;
 	struct powernowk8_target_arg pta = { .pol = pol, .targfreq = targfreq,
 					     .relation = relation };
 
-	/*
-	 * Must run on @pol->cpu.  cpufreq core is responsible for ensuring
-	 * that we're bound to the current CPU and pol->cpu stays online.
-	 */
-	if (smp_processor_id() == pol->cpu)
-		return powernowk8_target_fn(&pta);
-	else
-		return work_on_cpu(pol->cpu, powernowk8_target_fn, &pta);
+	this_cpu = get_cpu();
+	if (this_cpu == pol->cpu) {
+		ret = powernowk8_target_fn(&pta);
+		put_cpu();
+	} else {
+		put_cpu();
+		ret = work_on_cpu(pol->cpu, powernowk8_target_fn, &pta);
+	}
+
+	return ret;
 }
 
 /* Driver entry point to verify the policy and range of frequencies */
-- 
1.7.12


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