Re: [patch 2.6.30 2/4] CPUFREQ: fix (utter) cpufreq_add_dev mess

[Mathieu Desnoyers]

* Pallipadi, Venkatesh (venkatesh.pallipadi@xxxxxxxxx) wrote:
>  
> 
> >-----Original Message-----
> >From: Mathieu Desnoyers [mailto:mathieu.desnoyers@xxxxxxxxxx] 
> >Sent: Friday, July 03, 2009 8:25 AM
> >To: linux-kernel@xxxxxxxxxxxxxxx; Pallipadi, Venkatesh; Dave 
> >Jones; Thomas Renninger; cpufreq@xxxxxxxxxxxxxxx; 
> >kernel-testers@xxxxxxxxxxxxxxx; Ingo Molnar; rjw@xxxxxxx; Dave 
> >Young; Pekka Enberg
> >Cc: Mathieu Desnoyers; Li, Shaohua; Rusty Russell; 
> >sven.wegener@xxxxxxxxxxx
> >Subject: [patch 2.6.30 2/4] CPUFREQ: fix (utter) cpufreq_add_dev mess
> >
> >OK, I've tried to clean it up the best I could, but please 
> >test this with
> >concurrent cpu hotplug and cpufreq add/remove in loops. I'm 
> >sure we will make
> >other interesting findings.
> >
> 
> This is a good and needed cleanup of cpufreq_add_dev.
> 
> 
> >This is step one of fixing the overall locking dependency mess 
> >in cpufreq.
> >
> >Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
> >CC: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
> >CC: rjw@xxxxxxx
> >CC: mingo@xxxxxxx
> >CC: Shaohua Li <shaohua.li@xxxxxxxxx>
> >CC: Pekka Enberg <penberg@xxxxxxxxxxxxxx>
> >CC: Dave Young <hidave.darkstar@xxxxxxxxx>
> >CC: "Rafael J. Wysocki" <rjw@xxxxxxx>
> >CC: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
> >CC: sven.wegener@xxxxxxxxxxx
> >CC: cpufreq@xxxxxxxxxxxxxxx
> >CC: Thomas Renninger <trenn@xxxxxxx>
> >---
> > drivers/cpufreq/cpufreq.c |   65 
> >++++++++++++++++++++++++++++------------------
> > 1 file changed, 40 insertions(+), 25 deletions(-)
> >
> >Index: linux-2.6-lttng/drivers/cpufreq/cpufreq.c
> >===================================================================
> >--- linux-2.6-lttng.orig/drivers/cpufreq/cpufreq.c	
> >2009-07-02 23:59:08.000000000 -0400
> >+++ linux-2.6-lttng/drivers/cpufreq/cpufreq.c	2009-07-02 
> >23:59:09.000000000 -0400
> >@@ -763,6 +763,10 @@ static struct kobj_type ktype_cpufreq = 
> >  * cpufreq_add_dev - add a CPU device
> >  *
> >  * Adds the cpufreq interface for a CPU device.
> >+ *
> >+ * The Oracle says: try running cpufreq 
> >registration/unregistration concurrently
> >+ * with with cpu hotplugging and all hell will break loose. 
> >Tried to clean this
> >+ * mess up, but more thorough testing is needed. - Mathieu
> >  */
> > static int cpufreq_add_dev(struct sys_device *sys_dev)
> > {
> >@@ -806,15 +810,12 @@ static int cpufreq_add_dev(struct sys_de
> > 		goto nomem_out;
> > 	}
> > 	if (!alloc_cpumask_var(&policy->cpus, GFP_KERNEL)) {
> >-		kfree(policy);
> > 		ret = -ENOMEM;
> >-		goto nomem_out;
> >+		goto err_free_policy;
> > 	}
> > 	if (!zalloc_cpumask_var(&policy->related_cpus, GFP_KERNEL)) {
> >-		free_cpumask_var(policy->cpus);
> >-		kfree(policy);
> > 		ret = -ENOMEM;
> >-		goto nomem_out;
> >+		goto err_free_cpumask;
> > 	}
> > 
> > 	policy->cpu = cpu;
> >@@ -822,7 +823,8 @@ static int cpufreq_add_dev(struct sys_de
> > 
> > 	/* Initially set CPU itself as the policy_cpu */
> > 	per_cpu(policy_cpu, cpu) = cpu;
> >-	lock_policy_rwsem_write(cpu);
> >+	ret = (lock_policy_rwsem_write(cpu) < 0);
> >+	WARN_ON(ret);
> > 
> > 	init_completion(&policy->kobj_unregister);
> > 	INIT_WORK(&policy->update, handle_update);
> >@@ -835,7 +837,7 @@ static int cpufreq_add_dev(struct sys_de
> > 	ret = cpufreq_driver->init(policy);
> > 	if (ret) {
> > 		dprintk("initialization failed\n");
> >-		goto err_out;
> >+		goto err_unlock_policy;
> > 	}
> > 	policy->user_policy.min = policy->min;
> > 	policy->user_policy.max = policy->max;
> >@@ -860,15 +862,21 @@ static int cpufreq_add_dev(struct sys_de
> > 		/* Check for existing affected CPUs.
> > 		 * They may not be aware of it due to CPU Hotplug.
> > 		 */
> >-		managed_policy = cpufreq_cpu_get(j);		
> >/* FIXME: Where is this released?  What about error paths? */
> >+		managed_policy = cpufreq_cpu_get(j);
> > 		if (unlikely(managed_policy)) {
> > 
> > 			/* Set proper policy_cpu */
> > 			unlock_policy_rwsem_write(cpu);
> > 			per_cpu(policy_cpu, cpu) = managed_policy->cpu;
> > 
> >-			if (lock_policy_rwsem_write(cpu) < 0)
> >-				goto err_out_driver_exit;
> >+			if (lock_policy_rwsem_write(cpu) < 0) {
> >+				/* Should not go through policy 
> >unlock path */
> >+				if (cpufreq_driver->exit)
> >+					cpufreq_driver->exit(policy);
> >+				ret = -EBUSY;
> >+				cpufreq_cpu_put(managed_policy);
> >+				goto err_free_cpumask;
> >+			}
> > 
> > 			spin_lock_irqsave(&cpufreq_driver_lock, flags);
> > 			cpumask_copy(managed_policy->cpus, 
> >policy->cpus);
> >@@ -879,12 +887,14 @@ static int cpufreq_add_dev(struct sys_de
> > 			ret = sysfs_create_link(&sys_dev->kobj,
> > 						&managed_policy->kobj,
> > 						"cpufreq");
> >-			if (ret)
> >-				goto err_out_driver_exit;
> >-
> >-			cpufreq_debug_enable_ratelimit();
> >-			ret = 0;
> >-			goto err_out_driver_exit; /* call 
> >driver->exit() */
> >+			if (!ret)
> >+				cpufreq_cpu_put(managed_policy);
> 
> Looks like cpufreq_cpu_put is needed both with ret and !ret. No?
> 

No. ret == 0 path is a "success path" only creating a symlink, and
therefore __cpufreq_remove_dev() will take care of calling the
cpufreq_cpu_put() to decrement the reference count :

static int __cpufreq_remove_dev(struct sys_device *sys_dev)
{
...

        if (unlikely(cpu != data->cpu)) {
                dprintk("removing link\n");
                cpumask_clear_cpu(cpu, data->cpus);
                spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
                sysfs_remove_link(&sys_dev->kobj, "cpufreq");
                cpufreq_cpu_put(data);
                cpufreq_debug_enable_ratelimit();
                unlock_policy_rwsem_write(cpu);
                return 0;
        }

This is, at least, how I understand what is happening here.

Mathieu


> Thanks,
> Venki
> 
> >+			/*
> >+			 * Success. We only needed to be added 
> >to the mask.
> >+			 * Call driver->exit() because only the 
> >cpu parent of
> >+			 * the kobj needed to call init().
> >+			 */
> >+			goto out_driver_exit; /* call driver->exit() */
> > 		}
> > 	}
> > #endif
> >@@ -894,25 +904,25 @@ static int cpufreq_add_dev(struct sys_de
> > 	ret = kobject_init_and_add(&policy->kobj, 
> >&ktype_cpufreq, &sys_dev->kobj,
> > 				   "cpufreq");
> > 	if (ret)
> >-		goto err_out_driver_exit;
> >+		goto out_driver_exit;
> > 
> > 	/* set up files for this cpu device */
> > 	drv_attr = cpufreq_driver->attr;
> > 	while ((drv_attr) && (*drv_attr)) {
> > 		ret = sysfs_create_file(&policy->kobj, 
> >&((*drv_attr)->attr));
> > 		if (ret)
> >-			goto err_out_driver_exit;
> >+			goto err_out_kobj_put;
> > 		drv_attr++;
> > 	}
> > 	if (cpufreq_driver->get) {
> > 		ret = sysfs_create_file(&policy->kobj, 
> >&cpuinfo_cur_freq.attr);
> > 		if (ret)
> >-			goto err_out_driver_exit;
> >+			goto err_out_kobj_put;
> > 	}
> > 	if (cpufreq_driver->target) {
> > 		ret = sysfs_create_file(&policy->kobj, 
> >&scaling_cur_freq.attr);
> > 		if (ret)
> >-			goto err_out_driver_exit;
> >+			goto err_out_kobj_put;
> > 	}
> > 
> > 	spin_lock_irqsave(&cpufreq_driver_lock, flags);
> >@@ -930,12 +940,14 @@ static int cpufreq_add_dev(struct sys_de
> > 			continue;
> > 
> > 		dprintk("CPU %u already managed, adding link\n", j);
> >-		cpufreq_cpu_get(cpu);
> >+		managed_policy = cpufreq_cpu_get(cpu);
> > 		cpu_sys_dev = get_cpu_sysdev(j);
> > 		ret = sysfs_create_link(&cpu_sys_dev->kobj, 
> >&policy->kobj,
> > 					"cpufreq");
> >-		if (ret)
> >+		if (ret) {
> >+			cpufreq_cpu_put(managed_policy);
> > 			goto err_out_unregister;
> >+		}
> > 	}
> > 
> > 	policy->governor = NULL; /* to assure that the starting 
> >sequence is
> >@@ -967,17 +979,20 @@ err_out_unregister:
> > 		per_cpu(cpufreq_cpu_data, j) = NULL;
> > 	spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
> > 
> >+err_out_kobj_put:
> > 	kobject_put(&policy->kobj);
> > 	wait_for_completion(&policy->kobj_unregister);
> > 
> >-err_out_driver_exit:
> >+out_driver_exit:
> > 	if (cpufreq_driver->exit)
> > 		cpufreq_driver->exit(policy);
> > 
> >-err_out:
> >+err_unlock_policy:
> > 	unlock_policy_rwsem_write(cpu);
> >+err_free_cpumask:
> >+	free_cpumask_var(policy->cpus);
> >+err_free_policy:
> > 	kfree(policy);
> >-
> > nomem_out:
> > 	module_put(cpufreq_driver->owner);
> > module_out:
> >
> 
> 

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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