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Date: Fri, 3 Jul 2009 15:41:54 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To: "Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Dave Jones <davej@...hat.com>,
Thomas Renninger <trenn@...e.de>,
"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
"kernel-testers@...r.kernel.org" <kernel-testers@...r.kernel.org>,
Ingo Molnar <mingo@...e.hu>, "rjw@...k.pl" <rjw@...k.pl>,
Dave Young <hidave.darkstar@...il.com>,
Pekka Enberg <penberg@...helsinki.fi>,
"Li, Shaohua" <shaohua.li@...el.com>,
Rusty Russell <rusty@...tcorp.com.au>,
"sven.wegener@...aler.net" <sven.wegener@...aler.net>
Subject: Re: [patch 2.6.30 2/4] CPUFREQ: fix (utter) cpufreq_add_dev mess
* Pallipadi, Venkatesh (venkatesh.pallipadi@...el.com) wrote:
>
>
> >-----Original Message-----
> >From: Mathieu Desnoyers [mailto:mathieu.desnoyers@...ymtl.ca]
> >Sent: Friday, July 03, 2009 8:25 AM
> >To: linux-kernel@...r.kernel.org; Pallipadi, Venkatesh; Dave
> >Jones; Thomas Renninger; cpufreq@...r.kernel.org;
> >kernel-testers@...r.kernel.org; Ingo Molnar; rjw@...k.pl; Dave
> >Young; Pekka Enberg
> >Cc: Mathieu Desnoyers; Li, Shaohua; Rusty Russell;
> >sven.wegener@...aler.net
> >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@...ymtl.ca>
> >CC: Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
> >CC: rjw@...k.pl
> >CC: mingo@...e.hu
> >CC: Shaohua Li <shaohua.li@...el.com>
> >CC: Pekka Enberg <penberg@...helsinki.fi>
> >CC: Dave Young <hidave.darkstar@...il.com>
> >CC: "Rafael J. Wysocki" <rjw@...k.pl>
> >CC: Rusty Russell <rusty@...tcorp.com.au>
> >CC: sven.wegener@...aler.net
> >CC: cpufreq@...r.kernel.org
> >CC: Thomas Renninger <trenn@...e.de>
> >---
> > 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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