Convert semaphores to use waitlists

Saves one pointer per semaphore, shrinking it from 24 bytes to 16 bytes.
There aren't many semaphores left in the kernel, but there's no harm in
having semaphores use the same scheme as mutexes and rwsems.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>

diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index 57fb5f468ac2025ecb80775d420bebc9a867b998..cafbfe85d0181cbe9dd3e7dcf502907da004397b 100644 (file)
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -1198,7 +1198,7 @@ acpi_status acpi_os_delete_semaphore(acpi_handle handle)
 
        ACPI_DEBUG_PRINT((ACPI_DB_MUTEX, "Deleting semaphore[%p].\n", handle));
 
-       BUG_ON(!list_empty(&sem->wait_list));
+       BUG_ON(!wlist_empty(&sem->wait_list));
        kfree(sem);
        sem = NULL;
 

diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h
index dc368b8ce215ccc0f6a2b44a16dd2aaa603dbcd1..f83b6f6467367b3e72ec0c40d17217f69ab71058 100644 (file)
--- a/include/linux/semaphore.h
+++ b/include/linux/semaphore.h
@@ -16,14 +16,14 @@
 struct semaphore {
        raw_spinlock_t          lock;
        unsigned int            count;
-       struct list_head        wait_list;
+       struct wlist_head       wait_list;
 };
 
 #define __SEMAPHORE_INITIALIZER(name, n)                               \
 {                                                                      \
        .lock           = __RAW_SPIN_LOCK_UNLOCKED((name).lock),        \
        .count          = n,                                            \
-       .wait_list      = LIST_HEAD_INIT((name).wait_list),             \
+       .wait_list      = WLIST_HEAD_INIT,                              \
 }
 
 #define DEFINE_SEMAPHORE(name) \

diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c
index b8120abe594b893e164791afb0e4527d6ed3886c..56d5852e4c565a75144ca206349806f845101b50 100644 (file)
--- a/kernel/locking/semaphore.c
+++ b/kernel/locking/semaphore.c
@@ -180,7 +180,7 @@ void up(struct semaphore *sem)
        unsigned long flags;
 
        raw_spin_lock_irqsave(&sem->lock, flags);
-       if (likely(list_empty(&sem->wait_list)))
+       if (likely(wlist_empty(&sem->wait_list)))
                sem->count++;
        else
                __up(sem);
@@ -191,7 +191,7 @@ EXPORT_SYMBOL(up);
 /* Functions for the contended case */
 
 struct semaphore_waiter {
-       struct list_head list;
+       struct wlist_node list;
        struct task_struct *task;
        bool up;
 };
@@ -207,7 +207,7 @@ static inline int __sched __down_common(struct semaphore *sem, long state,
        struct task_struct *task = current;
        struct semaphore_waiter waiter;
 
-       list_add_tail(&waiter.list, &sem->wait_list);
+       wlist_add(&sem->wait_list, &waiter.list);
        waiter.task = task;
        waiter.up = false;
 
@@ -225,11 +225,11 @@ static inline int __sched __down_common(struct semaphore *sem, long state,
        }
 
  timed_out:
-       list_del(&waiter.list);
+       wlist_del(&sem->wait_list, &waiter.list);
        return -ETIME;
 
  interrupted:
-       list_del(&waiter.list);
+       wlist_del(&sem->wait_list, &waiter.list);
        return -EINTR;
 }
 
@@ -255,9 +255,8 @@ static noinline int __sched __down_timeout(struct semaphore *sem, long timeout)
 
 static noinline void __sched __up(struct semaphore *sem)
 {
-       struct semaphore_waiter *waiter = list_first_entry(&sem->wait_list,
+       struct semaphore_waiter *waiter = wlist_del_first_entry(&sem->wait_list,
                                                struct semaphore_waiter, list);
-       list_del(&waiter->list);
        waiter->up = true;
        wake_up_process(waiter->task);
 }