linux-kernel - [PATCH 8/14] cpumask: don't put a cpumask on the stack in x86...cpufreq/powernow-k8.c

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Date:	Tue, 3 Nov 2009 14:57:56 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	cpufreq@...r.kernel.org
Cc:	Dave Jones <davej@...hat.com>
Subject: [PATCH 8/14] cpumask: don't put a cpumask on the stack in x86...cpufreq/powernow-k8.c

It's still mugging the current process's cpumask, but as comment in
1ff6e97f1d says, it's not a trivial fix.

So, at least we can use a cpumask_var_t to do the Wrong Thing the Right Way :)

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
To: cpufreq@...r.kernel.org
Cc: Mark Langsdorf <mark.langsdorf@....com>
Cc: Dave Jones <davej@...hat.com>
---
 arch/x86/kernel/cpu/cpufreq/powernow-k8.c |   15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/cpufreq/powernow-k8.c b/arch/x86/kernel/cpu/cpufreq/powernow-k8.c
--- a/arch/x86/kernel/cpu/cpufreq/powernow-k8.c
+++ b/arch/x86/kernel/cpu/cpufreq/powernow-k8.c
@@ -1118,7 +1118,7 @@ static int transition_frequency_pstate(s
 static int powernowk8_target(struct cpufreq_policy *pol,
 		unsigned targfreq, unsigned relation)
 {
-	cpumask_t oldmask;
+	cpumask_var_t oldmask;
 	struct powernow_k8_data *data = per_cpu(powernow_data, pol->cpu);
 	u32 checkfid;
 	u32 checkvid;
@@ -1131,9 +1131,13 @@ static int powernowk8_target(struct cpuf
 	checkfid = data->currfid;
 	checkvid = data->currvid;
 
-	/* only run on specific CPU from here on */
-	oldmask = current->cpus_allowed;
-	set_cpus_allowed_ptr(current, &cpumask_of_cpu(pol->cpu));
+	/* only run on specific CPU from here on. */
+	/* This is poor form: use a workqueue or smp_call_function_single */
+	if (!alloc_cpumask_var(&oldmask, GFP_KERNEL))
+		return -ENOMEM;
+
+	cpumask_copy(oldmask, tsk_cpumask(current));
+	set_cpus_allowed_ptr(current, cpumask_of(pol->cpu));
 
 	if (smp_processor_id() != pol->cpu) {
 		printk(KERN_ERR PFX "limiting to cpu %u failed\n", pol->cpu);
@@ -1193,7 +1197,8 @@ static int powernowk8_target(struct cpuf
 	ret = 0;
 
 err_out:
-	set_cpus_allowed_ptr(current, &oldmask);
+	set_cpus_allowed_ptr(current, oldmask);
+	free_cpumask_var(oldmask);
 	return ret;
 }
 

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