Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=9e76988e9390a4ff4d171f690586d0c58186b47e
Commit: 9e76988e9390a4ff4d171f690586d0c58186b47e
Parent: b25e75899e449456409cfa1a3b042257c03d4355
Author: Venki Pallipadi <[EMAIL PROTECTED]>
AuthorDate: Fri Oct 26 10:18:21 2007 -0700
Committer: Dave Jones <[EMAIL PROTECTED]>
CommitDate: Wed Feb 6 22:57:58 2008 -0500
[CPUFREQ] Eliminate cpufreq_userspace scaling_setspeed deadlock
Eliminate cpufreq_userspace scaling_setspeed deadlock.
Luming Yu recently uncovered yet another cpufreq related deadlock.
One thread that continuously switches the governors and the other thread
that
repeatedly cats the contents of cpufreq directory causes both these threads
to
go into a deadlock.
Detailed examination of the deadlock showed the exact flow before the
deadlock
as:
Thread 1 Thread 2
________ ________
cats files under /sys/devices/.../cpufreq/
Set governor to userspace
Adds a new sysfs entry for
scaling_setspeed
cats files under /sys/devices/.../cpufreq/
Set governor to performance
Holds cpufreq_rw_sem in write
mode
Sends a STOP notify to
userspace governor
cat /sys/devices/.../cpufreq/scaling_setspeed
Gets a handle on the above sysfs entry with
sysfs_get_active
Blocks while trying to get cpufreq_rw_sem
in read mode
Remove a sysfs entry for
scaling_setspeed
Blocks on sysfs_deactivate
while waiting for earlier
get_active (on other thread)
to drain
At this point both threads go into deadlock and any other thread that tries
to
do anything with sysfs cpufreq will also block.
There seems to be no easy way to avoid this deadlock as long as
cpufreq_userspace adds/removes the sysfs entry under same kobject as
cpufreq.
Below patch moves scaling_setspeed to cpufreq.c, keeping it always and
calling
back the governor on read/write. This is the cleanest fix I could think of,
even though adding two callbacks in governor structure just for this seems
unnecessary.
Note that the change makes scaling_setspeed under /sys/.../cpufreq permanent
and returns <unsupported> when governor is not userspace.
Signed-off-by: Venkatesh Pallipadi <[EMAIL PROTECTED]>
Signed-off-by: Dave Jones <[EMAIL PROTECTED]>
---
drivers/cpufreq/cpufreq.c | 27 +++++++++++++++++++++++
drivers/cpufreq/cpufreq_userspace.c | 40 ++++++----------------------------
include/linux/cpufreq.h | 4 +++
3 files changed, 38 insertions(+), 33 deletions(-)
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 6133148..64926aa 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -601,6 +601,31 @@ static ssize_t show_affected_cpus (struct cpufreq_policy *
policy, char *buf)
return i;
}
+static ssize_t store_scaling_setspeed(struct cpufreq_policy *policy,
+ const char *buf, size_t count)
+{
+ unsigned int freq = 0;
+ unsigned int ret;
+
+ if (!policy->governor->store_setspeed)
+ return -EINVAL;
+
+ ret = sscanf(buf, "%u", &freq);
+ if (ret != 1)
+ return -EINVAL;
+
+ policy->governor->store_setspeed(policy, freq);
+
+ return count;
+}
+
+static ssize_t show_scaling_setspeed(struct cpufreq_policy *policy, char *buf)
+{
+ if (!policy->governor->show_setspeed)
+ return sprintf(buf, "<unsupported>\n");
+
+ return policy->governor->show_setspeed(policy, buf);
+}
#define define_one_ro(_name) \
static struct freq_attr _name = \
@@ -624,6 +649,7 @@ define_one_ro(affected_cpus);
define_one_rw(scaling_min_freq);
define_one_rw(scaling_max_freq);
define_one_rw(scaling_governor);
+define_one_rw(scaling_setspeed);
static struct attribute * default_attrs[] = {
&cpuinfo_min_freq.attr,
@@ -634,6 +660,7 @@ static struct attribute * default_attrs[] = {
&scaling_governor.attr,
&scaling_driver.attr,
&scaling_available_governors.attr,
+ &scaling_setspeed.attr,
NULL
};
diff --git a/drivers/cpufreq/cpufreq_userspace.c
b/drivers/cpufreq/cpufreq_userspace.c
index f8cdde4..cb2ac01 100644
--- a/drivers/cpufreq/cpufreq_userspace.c
+++ b/drivers/cpufreq/cpufreq_userspace.c
@@ -65,12 +65,12 @@ static struct notifier_block
userspace_cpufreq_notifier_block = {
/**
* cpufreq_set - set the CPU frequency
+ * @policy: pointer to policy struct where freq is being set
* @freq: target frequency in kHz
- * @cpu: CPU for which the frequency is to be set
*
* Sets the CPU frequency to freq.
*/
-static int cpufreq_set(unsigned int freq, struct cpufreq_policy *policy)
+static int cpufreq_set(struct cpufreq_policy *policy, unsigned int freq)
{
int ret = -EINVAL;
@@ -102,34 +102,11 @@ static int cpufreq_set(unsigned int freq, struct
cpufreq_policy *policy)
}
-/************************** sysfs interface ************************/
-static ssize_t show_speed (struct cpufreq_policy *policy, char *buf)
+static ssize_t show_speed(struct cpufreq_policy *policy, char *buf)
{
- return sprintf (buf, "%u\n", cpu_cur_freq[policy->cpu]);
+ return sprintf(buf, "%u\n", cpu_cur_freq[policy->cpu]);
}
-static ssize_t
-store_speed (struct cpufreq_policy *policy, const char *buf, size_t count)
-{
- unsigned int freq = 0;
- unsigned int ret;
-
- ret = sscanf (buf, "%u", &freq);
- if (ret != 1)
- return -EINVAL;
-
- cpufreq_set(freq, policy);
-
- return count;
-}
-
-static struct freq_attr freq_attr_scaling_setspeed =
-{
- .attr = { .name = "scaling_setspeed", .mode = 0644 },
- .show = show_speed,
- .store = store_speed,
-};
-
static int cpufreq_governor_userspace(struct cpufreq_policy *policy,
unsigned int event)
{
@@ -142,10 +119,6 @@ static int cpufreq_governor_userspace(struct
cpufreq_policy *policy,
return -EINVAL;
BUG_ON(!policy->cur);
mutex_lock(&userspace_mutex);
- rc = sysfs_create_file (&policy->kobj,
- &freq_attr_scaling_setspeed.attr);
- if (rc)
- goto start_out;
if (cpus_using_userspace_governor == 0) {
cpufreq_register_notifier(
@@ -160,7 +133,7 @@ static int cpufreq_governor_userspace(struct cpufreq_policy
*policy,
cpu_cur_freq[cpu] = policy->cur;
cpu_set_freq[cpu] = policy->cur;
dprintk("managing cpu %u started (%u - %u kHz, currently %u
kHz)\n", cpu, cpu_min_freq[cpu], cpu_max_freq[cpu], cpu_cur_freq[cpu]);
-start_out:
+
mutex_unlock(&userspace_mutex);
break;
case CPUFREQ_GOV_STOP:
@@ -176,7 +149,6 @@ start_out:
cpu_min_freq[cpu] = 0;
cpu_max_freq[cpu] = 0;
cpu_set_freq[cpu] = 0;
- sysfs_remove_file (&policy->kobj,
&freq_attr_scaling_setspeed.attr);
dprintk("managing cpu %u stopped\n", cpu);
mutex_unlock(&userspace_mutex);
break;
@@ -211,6 +183,8 @@ start_out:
struct cpufreq_governor cpufreq_gov_userspace = {
.name = "userspace",
.governor = cpufreq_governor_userspace,
+ .store_setspeed = cpufreq_set,
+ .show_setspeed = show_speed,
.owner = THIS_MODULE,
};
EXPORT_SYMBOL(cpufreq_gov_userspace);
diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index 23932d7..ddd8652 100644
--- a/include/linux/cpufreq.h
+++ b/include/linux/cpufreq.h
@@ -167,6 +167,10 @@ struct cpufreq_governor {
char name[CPUFREQ_NAME_LEN];
int (*governor) (struct cpufreq_policy *policy,
unsigned int event);
+ ssize_t (*show_setspeed) (struct cpufreq_policy *policy,
+ char *buf);
+ int (*store_setspeed) (struct cpufreq_policy *policy,
+ unsigned int freq);
unsigned int max_transition_latency; /* HW must be able to switch to
next freq faster than this value in nano secs or we
will fallback to performance governor */
-
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