[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>

2 files changed, 3 insertions, 5 deletions

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 43c44530ef9d..0ed1d4853c69 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -65,10 +65,9 @@ extern struct sysdev_class cpu_sysdev_class;
 
 #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 2038bd27b041..b0ad6f30679e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -908,7 +908,6 @@ do { if (atomic_dec_and_test(&(tsk)->usage)) __put_task_struct(tsk); } while(0)
 #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