Message-Id: <200906101552.17397.rusty@rustcorp.com.au>
Date:	Wed, 10 Jun 2009 15:52:15 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Yinghai Lu <yinghai@...nel.org>, Avi Kivity <avi@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>, cpufreq@...r.kernel.org,
	mark.langsdorf@....com
Subject: Re: [PATCH 4/6] x86/cpufreq: use cpumask_copy instead of =

On Wed, 10 Jun 2009 01:16:44 am Linus Torvalds wrote:
> On Tue, 9 Jun 2009, Rusty Russell wrote:
> >  	for_each_online_cpu(i) {
> > -		if (check_supported_cpu(i))
> > +		if (work_on_cpu(i, check_supported_cpu, NULL) == 0)
> >  			supported_cpus++;
>
> Please STOP USING THAT HORRIBLE "work_on_cpu()" crap.
>
> Is there any reason you do that? We've had to fix up the fallout from that
> kind of crazy crap several times.

Simplicity of translation, laziness, and reluctance to break stuff.  And a
nicer API.

It's called here on cpu bringup, but I'll change it (the code doesn't sleep).  
I've a couple of others in my queue I'll look at similarly.

powernow_k8_target is problematic: it grabs a mutex.  cpufreq people, is this 
called often?

Thanks,
Rusty.

Subject: cpumask: avoid playing with cpus_allowed in powernow-k8.c
From: Rusty Russell <rusty@...tcorp.com.au>

It's generally a very bad idea to mug some process's cpumask: it could
legitimately and reasonably be changed by root, which could break us
(if done before our code) or them (if we restore the wrong value).

I use work_on_cpu, which is slightly less efficient than the old code,
but the code is complex enough that using smp_call_function_single()
is not trivial.

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
To: davej@...hat.com
To: cpufreq@...r.kernel.org
Cc: mark.langsdorf@....com
---
 arch/x86/kernel/cpu/cpufreq/powernow-k8.c |  128 +++++++++++++++---------------
 1 file changed, 64 insertions(+), 64 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
@@ -510,41 +510,34 @@ static int core_voltage_post_transition(
 	return 0;
 }
 
-static int check_supported_cpu(unsigned int cpu)
+static void check_supported_cpu(void *_rc)
 {
-	cpumask_t oldmask;
 	u32 eax, ebx, ecx, edx;
-	unsigned int rc = 0;
+	int *rc = _rc;
 
-	oldmask = current->cpus_allowed;
-	set_cpus_allowed_ptr(current, &cpumask_of_cpu(cpu));
-
-	if (smp_processor_id() != cpu) {
-		printk(KERN_ERR PFX "limiting to cpu %u failed\n", cpu);
-		goto out;
-	}
+	*rc = -ENODEV;
 
 	if (current_cpu_data.x86_vendor != X86_VENDOR_AMD)
-		goto out;
+		return;
 
 	eax = cpuid_eax(CPUID_PROCESSOR_SIGNATURE);
 	if (((eax & CPUID_XFAM) != CPUID_XFAM_K8) &&
 	    ((eax & CPUID_XFAM) < CPUID_XFAM_10H))
-		goto out;
+		return;
 
 	if ((eax & CPUID_XFAM) == CPUID_XFAM_K8) {
 		if (((eax & CPUID_USE_XFAM_XMOD) != CPUID_USE_XFAM_XMOD) ||
 		    ((eax & CPUID_XMOD) > CPUID_XMOD_REV_MASK)) {
 			printk(KERN_INFO PFX
 				"Processor cpuid %x not supported\n", eax);
-			goto out;
+			return;
 		}
 
 		eax = cpuid_eax(CPUID_GET_MAX_CAPABILITIES);
 		if (eax < CPUID_FREQ_VOLT_CAPABILITIES) {
 			printk(KERN_INFO PFX
 			       "No frequency change capabilities detected\n");
-			goto out;
+			return;
 		}
 
 		cpuid(CPUID_FREQ_VOLT_CAPABILITIES, &eax, &ebx, &ecx, &edx);
@@ -552,21 +545,17 @@ static int check_supported_cpu(unsigned 
 			!= P_STATE_TRANSITION_CAPABLE) {
 			printk(KERN_INFO PFX
 				"Power state transitions not supported\n");
-			goto out;
+			return;
 		}
 	} else { /* must be a HW Pstate capable processor */
 		cpuid(CPUID_FREQ_VOLT_CAPABILITIES, &eax, &ebx, &ecx, &edx);
 		if ((edx & USE_HW_PSTATE) == USE_HW_PSTATE)
 			cpu_family = CPU_HW_PSTATE;
 		else
-			goto out;
+			return;
 	}
 
-	rc = 1;
-
-out:
-	set_cpus_allowed_ptr(current, &oldmask);
-	return rc;
+	*rc = 0;
 }
 
 static int check_pst_table(struct powernow_k8_data *data, struct pst_s *pst,
@@ -1141,11 +1130,16 @@ static int transition_frequency_pstate(s
 	return res;
 }
 
-/* Driver entry point to switch to the target frequency */
-static int powernowk8_target(struct cpufreq_policy *pol,
-		unsigned targfreq, unsigned relation)
+struct target_data {
+	struct cpufreq_policy *pol;
+	unsigned targfreq;
+	unsigned relation;
+};
+
+static long powernowk8_target_on_cpu(void *_tdata)
 {
-	cpumask_t oldmask;
+	struct target_data *tdata = _tdata;
+	struct cpufreq_policy *pol = tdata->pol;
 	struct powernow_k8_data *data = per_cpu(powernow_data, pol->cpu);
 	u32 checkfid;
 	u32 checkvid;
@@ -1158,22 +1152,13 @@ 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));
-
-	if (smp_processor_id() != pol->cpu) {
-		printk(KERN_ERR PFX "limiting to cpu %u failed\n", pol->cpu);
-		goto err_out;
-	}
-
 	if (pending_bit_stuck()) {
 		printk(KERN_ERR PFX "failing targ, change pending bit set\n");
 		goto err_out;
 	}
 
 	dprintk("targ: cpu %d, %d kHz, min %d, max %d, relation %d\n",
-		pol->cpu, targfreq, pol->min, pol->max, relation);
+		pol->cpu, tdata->targfreq, pol->min, pol->max, tdata->relation);
 
 	if (query_current_values_with_pending_wait(data))
 		goto err_out;
@@ -1193,7 +1178,8 @@ static int powernowk8_target(struct cpuf
 	}
 
 	if (cpufreq_frequency_table_target(pol, data->powernow_table,
-				targfreq, relation, &newstate))
+					   tdata->targfreq, tdata->relation,
+					   &newstate))
 		goto err_out;
 
 	mutex_lock(&fidvid_mutex);
@@ -1220,10 +1206,19 @@ static int powernowk8_target(struct cpuf
 	ret = 0;
 
 err_out:
-	set_cpus_allowed_ptr(current, &oldmask);
 	return ret;
 }
 
+/* Driver entry point to switch to the target frequency */
+static int powernowk8_target(struct cpufreq_policy *pol,
+			     unsigned targfreq, unsigned relation)
+{
+	struct target_data tdata = { .pol = pol,
+				     .targfreq = targfreq,
+				     .relation = relation };
+	return work_on_cpu(pol->cpu, powernowk8_target_on_cpu, &tdata);
+}
+
 /* Driver entry point to verify the policy and range of frequencies */
 static int powernowk8_verify(struct cpufreq_policy *pol)
 {
@@ -1235,6 +1230,32 @@ static int powernowk8_verify(struct cpuf
 	return cpufreq_frequency_table_verify(pol, data->powernow_table);
 }
 
+struct init_on_cpu {
+	struct powernow_k8_data *data;
+	int rc;
+};
+
+static void __cpuinit powernowk8_cpu_init_on_cpu(void *_init_on_cpu)
+{
+	struct init_on_cpu *init_on_cpu = _init_on_cpu;
+
+	if (pending_bit_stuck()) {
+		printk(KERN_ERR PFX "failing init, change pending bit set\n");
+		init_on_cpu->rc = -ENODEV;
+		return;
+	}
+
+	if (query_current_values_with_pending_wait(init_on_cpu->data)) {
+		init_on_cpu->rc = -ENODEV;
+		return;
+	}
+
+	if (cpu_family == CPU_OPTERON)
+		fidvid_msr_init();
+
+	init_on_cpu->rc = 0;
+}
+
 static const char ACPI_PSS_BIOS_BUG_MSG[] =
 	KERN_ERR FW_BUG PFX "No compatible ACPI _PSS objects found.\n"
 	KERN_ERR FW_BUG PFX "Try again with latest BIOS.\n";
@@ -1243,13 +1264,14 @@ static const char ACPI_PSS_BIOS_BUG_MSG[
 static int __cpuinit powernowk8_cpu_init(struct cpufreq_policy *pol)
 {
 	struct powernow_k8_data *data;
-	cpumask_t oldmask;
+	struct init_on_cpu init_on_cpu;
 	int rc;
 
 	if (!cpu_online(pol->cpu))
 		return -ENODEV;
 
-	if (!check_supported_cpu(pol->cpu))
+	smp_call_function_single(pol->cpu, check_supported_cpu, &rc, 1);
+	if (rc)
 		return -ENODEV;
 
 	data = kzalloc(sizeof(struct powernow_k8_data), GFP_KERNEL);
@@ -1289,27 +1311,12 @@ static int __cpuinit powernowk8_cpu_init
 		pol->cpuinfo.transition_latency = get_transition_latency(data);
 
 	/* only run on specific CPU from here on */
-	oldmask = current->cpus_allowed;
-	set_cpus_allowed_ptr(current, &cpumask_of_cpu(pol->cpu));
-
-	if (smp_processor_id() != pol->cpu) {
-		printk(KERN_ERR PFX "limiting to cpu %u failed\n", pol->cpu);
-		goto err_out_unmask;
-	}
-
-	if (pending_bit_stuck()) {
-		printk(KERN_ERR PFX "failing init, change pending bit set\n");
-		goto err_out_unmask;
-	}
-
-	if (query_current_values_with_pending_wait(data))
-		goto err_out_unmask;
-
-	if (cpu_family == CPU_OPTERON)
-		fidvid_msr_init();
-
-	/* run on any CPU again */
-	set_cpus_allowed_ptr(current, &oldmask);
+	init_on_cpu.data = data;
+	smp_call_function_single(data->cpu, powernowk8_cpu_init_on_cpu,
+				 &init_on_cpu, 1);
+	rc = init_on_cpu.rc;
+	if (rc != 0)
+		goto err_out_exit_acpi;
 
 	if (cpu_family == CPU_HW_PSTATE)
 		cpumask_copy(pol->cpus, cpumask_of(pol->cpu));
@@ -1346,8 +1353,7 @@ static int __cpuinit powernowk8_cpu_init
 
 	return 0;
 
-err_out_unmask:
-	set_cpus_allowed_ptr(current, &oldmask);
+err_out_exit_acpi:
 	powernow_k8_cpu_exit_acpi(data);
 
 err_out:
@@ -1372,12 +1378,20 @@ static int __devexit powernowk8_cpu_exit
 	return 0;
 }
 
+static void query_values_on_cpu(void *_err)
+{
+	int *err = _err;
+	struct powernow_k8_data *data = __get_cpu_var(powernow_data);
+
+	*err = query_current_values_with_pending_wait(data);
+}
+
 static unsigned int powernowk8_get(unsigned int cpu)
 {
 	struct powernow_k8_data *data;
-	cpumask_t oldmask = current->cpus_allowed;
 	unsigned int khz = 0;
 	unsigned int first;
+	int err;
 
 	first = cpumask_first(cpu_core_mask(cpu));
 	data = per_cpu(powernow_data, first);
@@ -1385,15 +1399,8 @@ static unsigned int powernowk8_get(unsig
 	if (!data)
 		return -EINVAL;
 
-	set_cpus_allowed_ptr(current, &cpumask_of_cpu(cpu));
-	if (smp_processor_id() != cpu) {
-		printk(KERN_ERR PFX
-			"limiting to CPU %d failed in powernowk8_get\n", cpu);
-		set_cpus_allowed_ptr(current, &oldmask);
-		return 0;
-	}
-
-	if (query_current_values_with_pending_wait(data))
+	smp_call_function_single(first, query_values_on_cpu, &err, true);
+	if (err)
 		goto out;
 
 	if (cpu_family == CPU_HW_PSTATE)
@@ -1404,7 +1411,6 @@ static unsigned int powernowk8_get(unsig
 
 
 out:
-	set_cpus_allowed_ptr(current, &oldmask);
 	return khz;
 }
 
@@ -1430,7 +1436,9 @@ static int __cpuinit powernowk8_init(voi
 	unsigned int i, supported_cpus = 0;
 
 	for_each_online_cpu(i) {
-		if (check_supported_cpu(i))
+		int rc;
+		smp_call_function_single(i, check_supported_cpu, &rc, 1);
+		if (rc == 0)
 			supported_cpus++;
 	}
 

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