Date:	Wed, 22 Jul 2015 17:37:18 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Rafael Wysocki <rjw@...ysocki.net>, linux@....linux.org.uk
Cc:	linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
	Viresh Kumar <viresh.kumar@...aro.org>,
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH V2] cpufreq: Fix double addition of sysfs links

Consider a dual core (0/1) system with two CPUs:
- sharing clock/voltage rails and hence cpufreq-policy
- CPU1 is offline while the cpufreq driver is registered
- cpufreq_add_dev() is called from subsys callback for CPU0 and we
  create the policy for the group of CPUs and create links for all
  present CPUs, i.e. CPU1 as well.
- cpufreq_add_dev() is called from subsys callback for CPU1, we find
  that the cpu is offline and we try to create a sysfs link for CPU1.

This results in double addtion of the sysfs link and we will get this:

WARNING: CPU: 0 PID: 1 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x60/0x7c()
sysfs: cannot create duplicate filename '/devices/system/cpu/cpu1/cpufreq'
Modules linked in:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.2.0-rc2+ #1704
Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
Backtrace:
[<c0013248>] (dump_backtrace) from [<c00133e4>] (show_stack+0x18/0x1c)
 r6:c01a1f30 r5:0000001f r4:00000000 r3:00000000
[<c00133cc>] (show_stack) from [<c076920c>] (dump_stack+0x7c/0x98)
[<c0769190>] (dump_stack) from [<c0029ab4>] (warn_slowpath_common+0x80/0xbc)
 r4:d74abbd0 r3:d74c0000
[<c0029a34>] (warn_slowpath_common) from [<c0029b94>] (warn_slowpath_fmt+0x38/0x40)
 r8:ffffffef r7:00000000 r6:d75a8960 r5:c0993280 r4:d6b4d000
[<c0029b60>] (warn_slowpath_fmt) from [<c01a1f30>] (sysfs_warn_dup+0x60/0x7c)
 r3:d6b4dfe7 r2:c0930750
[<c01a1ed0>] (sysfs_warn_dup) from [<c01a22c8>] (sysfs_do_create_link_sd+0xb8/0xc0)
 r6:d75a8960 r5:c0993280 r4:d00aba20
[<c01a2210>] (sysfs_do_create_link_sd) from [<c01a22fc>] (sysfs_create_link+0x2c/0x3c)
 r10:00000001 r8:c14db3c8 r7:d7b89010 r6:c0ae7c60 r5:d7b89010 r4:d00d1200
[<c01a22d0>] (sysfs_create_link) from [<c0506160>] (add_cpu_dev_symlink+0x34/0x5c)
[<c050612c>] (add_cpu_dev_symlink) from [<c05084d0>] (cpufreq_add_dev+0x674/0x794)
 r5:00000001 r4:00000000
[<c0507e5c>] (cpufreq_add_dev) from [<c03db114>] (subsys_interface_register+0x8c/0xd0)
 r10:00000003 r9:d7bb01f0 r8:c14db3c8 r7:00106738 r6:c0ae7c60 r5:c0acbd08
 r4:c0ae7e20
[<c03db088>] (subsys_interface_register) from [<c0508a2c>] (cpufreq_register_driver+0x104/0x1f4)

The check for offline-cpu in cpufreq_add_dev() is to ensure that link
gets added for the CPUs which weren't physically present earlier and
that misses the case where a CPU is offline while registering the
driver.

To fix this properly, don't create these links when the policy get
initialized. Rather wait for individual subsys callback for CPUs to
add/remove these links. This simplifies most of the code leaving
cpufreq_remove_dev().

The problem is that, we might remove cpu which was owner of policy->kobj
in sysfs, before other CPUs are removed. Fix this by the solution we
have been using until very recently, in which we move the kobject to any
other CPU, for which remove is yet to be called.

Tested on dual core exynos board with cpufreq-dt driver. The driver was
compiled as module and inserted/removed multiple times on a running
kernel.

Fixes: 87549141d516 ("cpufreq: Stop migrating sysfs files on hotplug")
Reported-and-suggested-by: Russell King <linux@....linux.org.uk>
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
V1->V2: Completely changed, please review again :)

@Rafael: I didn't review your solution and gave this one because I
thought Russell suggested the right thing. i.e. don't create links in
the beginning.

This is based of 4.2-rc3 and so your other patch,
https://patchwork.kernel.org/patch/6839031/ has to be rebased over it.

I didn't rebase this patch over yours for two reasons:
- Yours wasn't necessarily 4.2 material.
- I already mentioned a problem in that patch.

@Russell: I hope this will look much better than V1 to you. Please give
it a try once you get some time.

 drivers/cpufreq/cpufreq.c | 165 ++++++++++++++++++----------------------------
 include/linux/cpufreq.h   |   1 +
 2 files changed, 65 insertions(+), 101 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 26063afb3eba..81c2417e52f4 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -966,67 +966,6 @@ void cpufreq_sysfs_remove_file(const struct attribute *attr)
 }
 EXPORT_SYMBOL(cpufreq_sysfs_remove_file);
 
-static int add_cpu_dev_symlink(struct cpufreq_policy *policy, int cpu)
-{
-	struct device *cpu_dev;
-
-	pr_debug("%s: Adding symlink for CPU: %u\n", __func__, cpu);
-
-	if (!policy)
-		return 0;
-
-	cpu_dev = get_cpu_device(cpu);
-	if (WARN_ON(!cpu_dev))
-		return 0;
-
-	return sysfs_create_link(&cpu_dev->kobj, &policy->kobj, "cpufreq");
-}
-
-static void remove_cpu_dev_symlink(struct cpufreq_policy *policy, int cpu)
-{
-	struct device *cpu_dev;
-
-	pr_debug("%s: Removing symlink for CPU: %u\n", __func__, cpu);
-
-	cpu_dev = get_cpu_device(cpu);
-	if (WARN_ON(!cpu_dev))
-		return;
-
-	sysfs_remove_link(&cpu_dev->kobj, "cpufreq");
-}
-
-/* Add/remove symlinks for all related CPUs */
-static int cpufreq_add_dev_symlink(struct cpufreq_policy *policy)
-{
-	unsigned int j;
-	int ret = 0;
-
-	/* Some related CPUs might not be present (physically hotplugged) */
-	for_each_cpu_and(j, policy->related_cpus, cpu_present_mask) {
-		if (j == policy->kobj_cpu)
-			continue;
-
-		ret = add_cpu_dev_symlink(policy, j);
-		if (ret)
-			break;
-	}
-
-	return ret;
-}
-
-static void cpufreq_remove_dev_symlink(struct cpufreq_policy *policy)
-{
-	unsigned int j;
-
-	/* Some related CPUs might not be present (physically hotplugged) */
-	for_each_cpu_and(j, policy->related_cpus, cpu_present_mask) {
-		if (j == policy->kobj_cpu)
-			continue;
-
-		remove_cpu_dev_symlink(policy, j);
-	}
-}
-
 static int cpufreq_add_dev_interface(struct cpufreq_policy *policy,
 				     struct device *dev)
 {
@@ -1057,7 +996,7 @@ static int cpufreq_add_dev_interface(struct cpufreq_policy *policy,
 			return ret;
 	}
 
-	return cpufreq_add_dev_symlink(policy);
+	return 0;
 }
 
 static void cpufreq_init_policy(struct cpufreq_policy *policy)
@@ -1163,11 +1102,14 @@ static struct cpufreq_policy *cpufreq_policy_alloc(struct device *dev)
 	if (!zalloc_cpumask_var(&policy->related_cpus, GFP_KERNEL))
 		goto err_free_cpumask;
 
+	if (!zalloc_cpumask_var(&policy->symlinks, GFP_KERNEL))
+		goto err_free_related_cpumask;
+
 	ret = kobject_init_and_add(&policy->kobj, &ktype_cpufreq, &dev->kobj,
 				   "cpufreq");
 	if (ret) {
 		pr_err("%s: failed to init policy->kobj: %d\n", __func__, ret);
-		goto err_free_rcpumask;
+		goto err_free_symlink_cpumask;
 	}
 
 	INIT_LIST_HEAD(&policy->policy_list);
@@ -1184,7 +1126,9 @@ static struct cpufreq_policy *cpufreq_policy_alloc(struct device *dev)
 
 	return policy;
 
-err_free_rcpumask:
+err_free_symlink_cpumask:
+	free_cpumask_var(policy->symlinks);
+err_free_related_cpumask:
 	free_cpumask_var(policy->related_cpus);
 err_free_cpumask:
 	free_cpumask_var(policy->cpus);
@@ -1204,7 +1148,6 @@ static void cpufreq_policy_put_kobj(struct cpufreq_policy *policy, bool notify)
 					     CPUFREQ_REMOVE_POLICY, policy);
 
 	down_write(&policy->rwsem);
-	cpufreq_remove_dev_symlink(policy);
 	kobj = &policy->kobj;
 	cmp = &policy->kobj_unregister;
 	up_write(&policy->rwsem);
@@ -1234,6 +1177,7 @@ static void cpufreq_policy_free(struct cpufreq_policy *policy, bool notify)
 	write_unlock_irqrestore(&cpufreq_driver_lock, flags);
 
 	cpufreq_policy_put_kobj(policy, notify);
+	free_cpumask_var(policy->symlinks);
 	free_cpumask_var(policy->related_cpus);
 	free_cpumask_var(policy->cpus);
 	kfree(policy);
@@ -1252,26 +1196,37 @@ static int cpufreq_add_dev(struct device *dev, struct subsys_interface *sif)
 {
 	unsigned int j, cpu = dev->id;
 	int ret = -ENOMEM;
-	struct cpufreq_policy *policy;
+	struct cpufreq_policy *policy = per_cpu(cpufreq_cpu_data, cpu);
 	unsigned long flags;
 	bool recover_policy = !sif;
 
 	pr_debug("adding CPU %u\n", cpu);
 
+	/* sysfs links are only created on subsys callback */
+	if (sif && policy) {
+		pr_debug("%s: Adding symlink for CPU: %u\n", __func__, cpu);
+		ret = sysfs_create_link(&dev->kobj, &policy->kobj, "cpufreq");
+		if (ret) {
+			dev_err(dev, "%s: Failed to create link for cpu %d (%d)\n",
+				__func__, cpu, ret);
+			return ret;
+		}
+
+		/* Track CPUs for which sysfs links are created */
+		cpumask_set_cpu(cpu, policy->symlinks);
+	}
+
 	/*
-	 * Only possible if 'cpu' wasn't physically present earlier and we are
-	 * here from subsys_interface add callback. A hotplug notifier will
-	 * follow and we will handle it like logical CPU hotplug then. For now,
-	 * just create the sysfs link.
+	 * A hotplug notifier will follow and we will take care of rest
+	 * of the initialization then.
 	 */
 	if (cpu_is_offline(cpu))
-		return add_cpu_dev_symlink(per_cpu(cpufreq_cpu_data, cpu), cpu);
+		return 0;
 
 	if (!down_read_trylock(&cpufreq_rwsem))
 		return 0;
 
 	/* Check if this CPU already has a policy to manage it */
-	policy = per_cpu(cpufreq_cpu_data, cpu);
 	if (policy && !policy_is_inactive(policy)) {
 		WARN_ON(!cpumask_test_cpu(cpu, policy->related_cpus));
 		ret = cpufreq_add_policy_cpu(policy, cpu, dev);
@@ -1506,10 +1461,6 @@ static int __cpufreq_remove_dev_finish(struct device *dev,
 	if (cpufreq_driver->exit)
 		cpufreq_driver->exit(policy);
 
-	/* Free the policy only if the driver is getting removed. */
-	if (sif)
-		cpufreq_policy_free(policy, true);
-
 	return 0;
 }
 
@@ -1521,42 +1472,54 @@ static int __cpufreq_remove_dev_finish(struct device *dev,
 static int cpufreq_remove_dev(struct device *dev, struct subsys_interface *sif)
 {
 	unsigned int cpu = dev->id;
+	struct cpufreq_policy *policy = per_cpu(cpufreq_cpu_data, cpu);
 	int ret;
 
-	/*
-	 * Only possible if 'cpu' is getting physically removed now. A hotplug
-	 * notifier should have already been called and we just need to remove
-	 * link or free policy here.
-	 */
-	if (cpu_is_offline(cpu)) {
-		struct cpufreq_policy *policy = per_cpu(cpufreq_cpu_data, cpu);
-		struct cpumask mask;
+	if (!policy)
+		return 0;
 
-		if (!policy)
-			return 0;
+	if (cpu_online(cpu)) {
+		ret = __cpufreq_remove_dev_prepare(dev, sif);
+		if (!ret)
+			ret = __cpufreq_remove_dev_finish(dev, sif);
+		if (ret)
+			return ret;
+	}
 
-		cpumask_copy(&mask, policy->related_cpus);
-		cpumask_clear_cpu(cpu, &mask);
+	/* sysfs links are removed only on subsys callback */
+	if (cpumask_test_cpu(cpu, policy->symlinks)) {
+		dev_dbg(dev, "%s: Removing symlink for CPU: %u\n", __func__,
+			cpu);
+		cpumask_clear_cpu(cpu, policy->symlinks);
+		sysfs_remove_link(&dev->kobj, "cpufreq");
+		return 0;
+	}
 
+	if (cpumask_weight(policy->symlinks)) {
 		/*
-		 * Free policy only if all policy->related_cpus are removed
-		 * physically.
+		 * Okay, we still have some CPUs left. Transfer the ownership of
+		 * policy to one of them. Would be better to pass that to
+		 * cpumask_last() as that will be the last CPU to get removed,
+		 * but there is no API to get last cpu of the mask. Lets move it
+		 * to the first cpu in the mask.
 		 */
-		if (cpumask_intersects(&mask, cpu_present_mask)) {
-			remove_cpu_dev_symlink(policy, cpu);
-			return 0;
-		}
+		int new_cpu = cpumask_first(policy->symlinks);
+		struct device *new_dev = get_cpu_device(new_cpu);
 
-		cpufreq_policy_free(policy, true);
-		return 0;
-	}
+		dev_dbg(dev, "%s: Migrating kobj from %d to %d\n", __func__,
+			cpu, new_cpu);
 
-	ret = __cpufreq_remove_dev_prepare(dev, sif);
+		cpumask_clear_cpu(new_cpu, policy->symlinks);
+		sysfs_remove_link(&new_dev->kobj, "cpufreq");
 
-	if (!ret)
-		ret = __cpufreq_remove_dev_finish(dev, sif);
+		policy->kobj_cpu = new_cpu;
+		WARN_ON(kobject_move(&policy->kobj, &new_dev->kobj));
+	} else {
+		/* This is the last CPU to be removed */
+		cpufreq_policy_free(policy, true);
+	}
 
-	return ret;
+	return 0;
 }
 
 static void handle_update(struct work_struct *work)
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 29ad97c34fd5..c748d1cd0815 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -62,6 +62,7 @@ struct cpufreq_policy {
 	/* CPUs sharing clock, require sw coordination */
 	cpumask_var_t		cpus;	/* Online CPUs only */
 	cpumask_var_t		related_cpus; /* Online + Offline CPUs */
+	cpumask_var_t		symlinks; /* CPUs for which cpufreq sysfs directory is present */
 
 	unsigned int		shared_type; /* ACPI: ANY or ALL affected CPUs
 						should set cpufreq */
-- 
2.4.0

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