[PATCH] clean up lock_cpu_hotplug() in cpufreq
There are some callers in cpufreq hotplug notify path that the lowest
function calls lock_cpu_hotplug(). The lock is already held during
cpu_up() and cpu_down() calls when the notify calls are broadcast to
registered clients.
Ideally if possible, we could disable_preempt() at the highest caller and
make sure we dont sleep in the path down in cpufreq->driver_target() calls
but the calls are so intertwined and cumbersome to cleanup.
Hence we consistently use lock_cpu_hotplug() and unlock_cpu_hotplug() in
all places.
- Removed export of cpucontrol semaphore and made it static.
- removed explicit uses of up/down with lock_cpu_hotplug()
so we can keep track of the the callers in same thread context and
just keep refcounts without calling a down() that causes a deadlock.
- Removed current_in_hotplug() uses
- Removed PF_HOTPLUG_CPU in sched.h introduced for the current_in_hotplug()
temporary workaround.
Tested with insmod of cpufreq_stat.ko, and logical online/offline
to make sure we dont have any hang situations.
Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Cc: Zwane Mwaikambo <zwane@linuxpower.ca>
Cc: Shaohua Li <shaohua.li@intel.com>
Cc: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 1c0f62d..815902c 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1113,21 +1113,13 @@
{
int retval = -EINVAL;
- /*
- * If we are already in context of hotplug thread, we dont need to
- * acquire the hotplug lock. Otherwise acquire cpucontrol to prevent
- * hotplug from removing this cpu that we are working on.
- */
- if (!current_in_cpu_hotplug())
- lock_cpu_hotplug();
-
+ lock_cpu_hotplug();
dprintk("target for CPU %u: %u kHz, relation %u\n", policy->cpu,
target_freq, relation);
if (cpu_online(policy->cpu) && cpufreq_driver->target)
retval = cpufreq_driver->target(policy, target_freq, relation);
- if (!current_in_cpu_hotplug())
- unlock_cpu_hotplug();
+ unlock_cpu_hotplug();
return retval;
}
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 43c4453..0ed1d48 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -65,10 +65,9 @@
#ifdef CONFIG_HOTPLUG_CPU
/* Stop CPUs going up and down. */
-extern struct semaphore cpucontrol;
-#define lock_cpu_hotplug() down(&cpucontrol)
-#define unlock_cpu_hotplug() up(&cpucontrol)
-#define lock_cpu_hotplug_interruptible() down_interruptible(&cpucontrol)
+extern void lock_cpu_hotplug(void);
+extern void unlock_cpu_hotplug(void);
+extern int lock_cpu_hotplug_interruptible(void);
#define hotcpu_notifier(fn, pri) { \
static struct notifier_block fn##_nb = \
{ .notifier_call = fn, .priority = pri }; \
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 2038bd2..b0ad6f3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -908,7 +908,6 @@
#define PF_SYNCWRITE 0x00200000 /* I am doing a sync write */
#define PF_BORROWED_MM 0x00400000 /* I am a kthread doing use_mm */
#define PF_RANDOMIZE 0x00800000 /* randomize virtual address space */
-#define PF_HOTPLUG_CPU 0x01000000 /* Currently performing CPU hotplug */
/*
* Only the _current_ task can read/write to tsk->flags, but other
diff --git a/kernel/cpu.c b/kernel/cpu.c
index d61ba88..e882c6b 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -16,47 +16,76 @@
#include <asm/semaphore.h>
/* This protects CPUs going up and down... */
-DECLARE_MUTEX(cpucontrol);
-EXPORT_SYMBOL_GPL(cpucontrol);
+static DECLARE_MUTEX(cpucontrol);
static struct notifier_block *cpu_chain;
-/*
- * Used to check by callers if they need to acquire the cpucontrol
- * or not to protect a cpu from being removed. Its sometimes required to
- * call these functions both for normal operations, and in response to
- * a cpu being added/removed. If the context of the call is in the same
- * thread context as a CPU hotplug thread, we dont need to take the lock
- * since its already protected
- * check drivers/cpufreq/cpufreq.c for its usage - Ashok Raj
- */
+#ifdef CONFIG_HOTPLUG_CPU
+static struct task_struct *lock_cpu_hotplug_owner;
+static int lock_cpu_hotplug_depth;
-int current_in_cpu_hotplug(void)
+static int __lock_cpu_hotplug(int interruptible)
{
- return (current->flags & PF_HOTPLUG_CPU);
+ int ret = 0;
+
+ if (lock_cpu_hotplug_owner != current) {
+ if (interruptible)
+ ret = down_interruptible(&cpucontrol);
+ else
+ down(&cpucontrol);
+ }
+
+ /*
+ * Set only if we succeed in locking
+ */
+ if (!ret) {
+ lock_cpu_hotplug_depth++;
+ lock_cpu_hotplug_owner = current;
+ }
+
+ return ret;
}
-EXPORT_SYMBOL_GPL(current_in_cpu_hotplug);
+void lock_cpu_hotplug(void)
+{
+ __lock_cpu_hotplug(0);
+}
+EXPORT_SYMBOL_GPL(lock_cpu_hotplug);
+void unlock_cpu_hotplug(void)
+{
+ if (--lock_cpu_hotplug_depth == 0) {
+ lock_cpu_hotplug_owner = NULL;
+ up(&cpucontrol);
+ }
+}
+EXPORT_SYMBOL_GPL(unlock_cpu_hotplug);
+
+int lock_cpu_hotplug_interruptible(void)
+{
+ return __lock_cpu_hotplug(1);
+}
+EXPORT_SYMBOL_GPL(lock_cpu_hotplug_interruptible);
+#endif /* CONFIG_HOTPLUG_CPU */
/* Need to know about CPUs going up/down? */
int register_cpu_notifier(struct notifier_block *nb)
{
int ret;
- if ((ret = down_interruptible(&cpucontrol)) != 0)
+ if ((ret = lock_cpu_hotplug_interruptible()) != 0)
return ret;
ret = notifier_chain_register(&cpu_chain, nb);
- up(&cpucontrol);
+ unlock_cpu_hotplug();
return ret;
}
EXPORT_SYMBOL(register_cpu_notifier);
void unregister_cpu_notifier(struct notifier_block *nb)
{
- down(&cpucontrol);
+ lock_cpu_hotplug();
notifier_chain_unregister(&cpu_chain, nb);
- up(&cpucontrol);
+ unlock_cpu_hotplug();
}
EXPORT_SYMBOL(unregister_cpu_notifier);
@@ -112,13 +141,6 @@
goto out;
}
- /*
- * Leave a trace in current->flags indicating we are already in
- * process of performing CPU hotplug. Callers can check if cpucontrol
- * is already acquired by current thread, and if so not cause
- * a dead lock by not acquiring the lock
- */
- current->flags |= PF_HOTPLUG_CPU;
err = notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,
(void *)(long)cpu);
if (err == NOTIFY_BAD) {
@@ -171,7 +193,6 @@
out_allowed:
set_cpus_allowed(current, old_allowed);
out:
- current->flags &= ~PF_HOTPLUG_CPU;
unlock_cpu_hotplug();
return err;
}
@@ -182,7 +203,7 @@
int ret;
void *hcpu = (void *)(long)cpu;
- if ((ret = down_interruptible(&cpucontrol)) != 0)
+ if ((ret = lock_cpu_hotplug_interruptible()) != 0)
return ret;
if (cpu_online(cpu) || !cpu_present(cpu)) {
@@ -190,11 +211,6 @@
goto out;
}
- /*
- * Leave a trace in current->flags indicating we are already in
- * process of performing CPU hotplug.
- */
- current->flags |= PF_HOTPLUG_CPU;
ret = notifier_call_chain(&cpu_chain, CPU_UP_PREPARE, hcpu);
if (ret == NOTIFY_BAD) {
printk("%s: attempt to bring up CPU %u failed\n",
@@ -217,7 +233,6 @@
if (ret != 0)
notifier_call_chain(&cpu_chain, CPU_UP_CANCELED, hcpu);
out:
- current->flags &= ~PF_HOTPLUG_CPU;
- up(&cpucontrol);
+ unlock_cpu_hotplug();
return ret;
}
