[PATCH] cpufreq: Fix sysfs deadlock with concurrent hotplug/frequency switch
From: Stephen Boyd
Date: Thu Jul 19 2012 - 21:57:11 EST
Running one program that continuously hotplugs and replugs a cpu
concurrently with another program that continuously writes to the
scaling_setspeed node eventually deadlocks with:
=============================================
[ INFO: possible recursive locking detected ]
3.4.0 #37 Tainted: G W
---------------------------------------------
filemonkey/122 is trying to acquire lock:
(s_active#13){++++.+}, at: [<c01a3d28>] sysfs_remove_dir+0x9c/0xb4
but task is already holding lock:
(s_active#13){++++.+}, at: [<c01a22f0>] sysfs_write_file+0xe8/0x140
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(s_active#13);
lock(s_active#13);
*** DEADLOCK ***
May be due to missing lock nesting notation
2 locks held by filemonkey/122:
#0: (&buffer->mutex){+.+.+.}, at: [<c01a2230>] sysfs_write_file+0x28/0x140
#1: (s_active#13){++++.+}, at: [<c01a22f0>] sysfs_write_file+0xe8/0x140
stack backtrace:
[<c0014fcc>] (unwind_backtrace+0x0/0x120) from [<c00ca600>] (validate_chain+0x6f8/0x1054)
[<c00ca600>] (validate_chain+0x6f8/0x1054) from [<c00cb778>] (__lock_acquire+0x81c/0x8d8)
[<c00cb778>] (__lock_acquire+0x81c/0x8d8) from [<c00cb9c0>] (lock_acquire+0x18c/0x1e8)
[<c00cb9c0>] (lock_acquire+0x18c/0x1e8) from [<c01a3ba8>] (sysfs_addrm_finish+0xd0/0x180)
[<c01a3ba8>] (sysfs_addrm_finish+0xd0/0x180) from [<c01a3d28>] (sysfs_remove_dir+0x9c/0xb4)
[<c01a3d28>] (sysfs_remove_dir+0x9c/0xb4) from [<c02d0e5c>] (kobject_del+0x10/0x38)
[<c02d0e5c>] (kobject_del+0x10/0x38) from [<c02d0f74>] (kobject_release+0xf0/0x194)
[<c02d0f74>] (kobject_release+0xf0/0x194) from [<c0565a98>] (cpufreq_cpu_put+0xc/0x24)
[<c0565a98>] (cpufreq_cpu_put+0xc/0x24) from [<c05683f0>] (store+0x6c/0x74)
[<c05683f0>] (store+0x6c/0x74) from [<c01a2314>] (sysfs_write_file+0x10c/0x140)
[<c01a2314>] (sysfs_write_file+0x10c/0x140) from [<c014af44>] (vfs_write+0xb0/0x128)
[<c014af44>] (vfs_write+0xb0/0x128) from [<c014b06c>] (sys_write+0x3c/0x68)
[<c014b06c>] (sys_write+0x3c/0x68) from [<c000e0e0>] (ret_fast_syscall+0x0/0x3c)
This is because store() in cpufreq.c indirectly calls
kobject_get() via cpufreq_cpu_get() and is the last one to call
kobject_put() via cpufreq_cpu_put(). Sysfs code should not call
kobject_get() or kobject_put() directly (see the comment around
sysfs_schedule_callback() for more information).
Fix this deadlock by introducing two new functions:
struct cpufreq_policy *cpufreq_cpu_get_sysfs(unsigned int cpu)
void cpufreq_cpu_put_sysfs(struct cpufreq_policy *data)
which do the same thing as cpufreq_cpu_{get,put}() but don't call
kobject functions.
To easily trigger this deadlock you can apply a one line patch to
the store() function in cpufreq.c
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index a290771..62af12d 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -675,6 +675,7 @@ static ssize_t store(struct kobject *kobj
unlock_policy_rwsem_write(policy->cpu);
fail:
+ msleep(10000);
cpufreq_cpu_put_sysfs(policy);
no_policy:
return ret;
and then write scaling_setspeed in one task and offline the cpu
in another. The first task will hang and be detected by the hung
task detector.
Signed-off-by: Stephen Boyd <sboyd@xxxxxxxxxxxxxx>
---
Before you ask, I've seen the comment above cpufreq_add_dev() about
concurrent hotplug/cpufreq.
drivers/cpufreq/cpufreq.c | 35 +++++++++++++++++++++++++++--------
1 file changed, 27 insertions(+), 8 deletions(-)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 7f2f149..a290771 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -138,7 +138,7 @@ void disable_cpufreq(void)
static LIST_HEAD(cpufreq_governor_list);
static DEFINE_MUTEX(cpufreq_governor_mutex);
-struct cpufreq_policy *cpufreq_cpu_get(unsigned int cpu)
+static struct cpufreq_policy *__cpufreq_cpu_get(unsigned int cpu, int sysfs)
{
struct cpufreq_policy *data;
unsigned long flags;
@@ -162,7 +162,7 @@ struct cpufreq_policy *cpufreq_cpu_get(unsigned int cpu)
if (!data)
goto err_out_put_module;
- if (!kobject_get(&data->kobj))
+ if (!sysfs && !kobject_get(&data->kobj))
goto err_out_put_module;
spin_unlock_irqrestore(&cpufreq_driver_lock, flags);
@@ -175,16 +175,35 @@ err_out_unlock:
err_out:
return NULL;
}
+
+struct cpufreq_policy *cpufreq_cpu_get(unsigned int cpu)
+{
+ return __cpufreq_cpu_get(cpu, 0);
+}
EXPORT_SYMBOL_GPL(cpufreq_cpu_get);
+static struct cpufreq_policy *cpufreq_cpu_get_sysfs(unsigned int cpu)
+{
+ return __cpufreq_cpu_get(cpu, 1);
+}
-void cpufreq_cpu_put(struct cpufreq_policy *data)
+static void __cpufreq_cpu_put(struct cpufreq_policy *data, int sysfs)
{
- kobject_put(&data->kobj);
+ if (!sysfs)
+ kobject_put(&data->kobj);
module_put(cpufreq_driver->owner);
}
+
+void cpufreq_cpu_put(struct cpufreq_policy *data)
+{
+ __cpufreq_cpu_put(data, 0);
+}
EXPORT_SYMBOL_GPL(cpufreq_cpu_put);
+static void cpufreq_cpu_put_sysfs(struct cpufreq_policy *data)
+{
+ __cpufreq_cpu_put(data, 1);
+}
/*********************************************************************
* EXTERNALLY AFFECTING FREQUENCY CHANGES *
@@ -617,7 +636,7 @@ static ssize_t show(struct kobject *kobj, struct attribute *attr, char *buf)
struct cpufreq_policy *policy = to_policy(kobj);
struct freq_attr *fattr = to_attr(attr);
ssize_t ret = -EINVAL;
- policy = cpufreq_cpu_get(policy->cpu);
+ policy = cpufreq_cpu_get_sysfs(policy->cpu);
if (!policy)
goto no_policy;
@@ -631,7 +650,7 @@ static ssize_t show(struct kobject *kobj, struct attribute *attr, char *buf)
unlock_policy_rwsem_read(policy->cpu);
fail:
- cpufreq_cpu_put(policy);
+ cpufreq_cpu_put_sysfs(policy);
no_policy:
return ret;
}
@@ -642,7 +661,7 @@ static ssize_t store(struct kobject *kobj, struct attribute *attr,
struct cpufreq_policy *policy = to_policy(kobj);
struct freq_attr *fattr = to_attr(attr);
ssize_t ret = -EINVAL;
- policy = cpufreq_cpu_get(policy->cpu);
+ policy = cpufreq_cpu_get_sysfs(policy->cpu);
if (!policy)
goto no_policy;
@@ -656,7 +675,7 @@ static ssize_t store(struct kobject *kobj, struct attribute *attr,
unlock_policy_rwsem_write(policy->cpu);
fail:
- cpufreq_cpu_put(policy);
+ cpufreq_cpu_put_sysfs(policy);
no_policy:
return ret;
}
--
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
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