rwsem: make the waiter type an enumeration rather than a bitmask
Michel Lespinasse [Tue, 7 May 2013 13:45:49 +0000 (06:45 -0700)]
We are not planning to add some new waiter flags, so we can convert the
waiter type into an enumeration.

Background: David Howells suggested I do this back when I tried adding
a new waiter type for unfair readers. However, I believe the cleanup
applies regardless of that use case.

Signed-off-by: Michel Lespinasse <walken@google.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Acked-by: Davidlohr Bueso <davidlohr.bueso@hp.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/rwsem-spinlock.c
lib/rwsem.c

index 7542afb..5f117f3 100644 (file)
@@ -9,12 +9,15 @@
 #include <linux/sched.h>
 #include <linux/export.h>
 
+enum rwsem_waiter_type {
+       RWSEM_WAITING_FOR_WRITE,
+       RWSEM_WAITING_FOR_READ
+};
+
 struct rwsem_waiter {
        struct list_head list;
        struct task_struct *task;
-       unsigned int flags;
-#define RWSEM_WAITING_FOR_READ 0x00000001
-#define RWSEM_WAITING_FOR_WRITE        0x00000002
+       enum rwsem_waiter_type type;
 };
 
 int rwsem_is_locked(struct rw_semaphore *sem)
@@ -68,7 +71,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
        waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
 
        if (!wakewrite) {
-               if (waiter->flags & RWSEM_WAITING_FOR_WRITE)
+               if (waiter->type == RWSEM_WAITING_FOR_WRITE)
                        goto out;
                goto dont_wake_writers;
        }
@@ -78,7 +81,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
         * to -1 here to indicate we get the lock. Instead, we wake it up
         * to let it go get it again.
         */
-       if (waiter->flags & RWSEM_WAITING_FOR_WRITE) {
+       if (waiter->type == RWSEM_WAITING_FOR_WRITE) {
                wake_up_process(waiter->task);
                goto out;
        }
@@ -86,7 +89,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
        /* grant an infinite number of read locks to the front of the queue */
  dont_wake_writers:
        woken = 0;
-       while (waiter->flags & RWSEM_WAITING_FOR_READ) {
+       while (waiter->type == RWSEM_WAITING_FOR_READ) {
                struct list_head *next = waiter->list.next;
 
                list_del(&waiter->list);
@@ -144,7 +147,7 @@ void __sched __down_read(struct rw_semaphore *sem)
 
        /* set up my own style of waitqueue */
        waiter.task = tsk;
-       waiter.flags = RWSEM_WAITING_FOR_READ;
+       waiter.type = RWSEM_WAITING_FOR_READ;
        get_task_struct(tsk);
 
        list_add_tail(&waiter.list, &sem->wait_list);
@@ -201,7 +204,7 @@ void __sched __down_write_nested(struct rw_semaphore *sem, int subclass)
        /* set up my own style of waitqueue */
        tsk = current;
        waiter.task = tsk;
-       waiter.flags = RWSEM_WAITING_FOR_WRITE;
+       waiter.type = RWSEM_WAITING_FOR_WRITE;
        list_add_tail(&waiter.list, &sem->wait_list);
 
        /* wait for someone to release the lock */
index ad5e0df..672eb33 100644 (file)
@@ -30,12 +30,15 @@ void __init_rwsem(struct rw_semaphore *sem, const char *name,
 
 EXPORT_SYMBOL(__init_rwsem);
 
+enum rwsem_waiter_type {
+       RWSEM_WAITING_FOR_WRITE,
+       RWSEM_WAITING_FOR_READ
+};
+
 struct rwsem_waiter {
        struct list_head list;
        struct task_struct *task;
-       unsigned int flags;
-#define RWSEM_WAITING_FOR_READ 0x00000001
-#define RWSEM_WAITING_FOR_WRITE        0x00000002
+       enum rwsem_waiter_type type;
 };
 
 /* Wake types for __rwsem_do_wake().  Note that RWSEM_WAKE_NO_ACTIVE and
@@ -65,7 +68,7 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wake_type)
        signed long woken, loop, adjustment;
 
        waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
-       if (!(waiter->flags & RWSEM_WAITING_FOR_WRITE))
+       if (waiter->type != RWSEM_WAITING_FOR_WRITE)
                goto readers_only;
 
        if (wake_type == RWSEM_WAKE_READ_OWNED)
@@ -112,10 +115,10 @@ __rwsem_do_wake(struct rw_semaphore *sem, int wake_type)
                waiter = list_entry(waiter->list.next,
                                        struct rwsem_waiter, list);
 
-       } while (waiter->flags & RWSEM_WAITING_FOR_READ);
+       } while (waiter->type != RWSEM_WAITING_FOR_WRITE);
 
        adjustment = woken * RWSEM_ACTIVE_READ_BIAS;
-       if (waiter->flags & RWSEM_WAITING_FOR_READ)
+       if (waiter->type != RWSEM_WAITING_FOR_WRITE)
                /* hit end of list above */
                adjustment -= RWSEM_WAITING_BIAS;
 
@@ -148,7 +151,7 @@ static int try_get_writer_sem(struct rw_semaphore *sem,
 
        /* only steal when first waiter is writing */
        fwaiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
-       if (!(fwaiter->flags & RWSEM_WAITING_FOR_WRITE))
+       if (fwaiter->type != RWSEM_WAITING_FOR_WRITE)
                return 0;
 
        adjustment = RWSEM_ACTIVE_WRITE_BIAS;
@@ -179,7 +182,7 @@ try_again_write:
  */
 static struct rw_semaphore __sched *
 rwsem_down_failed_common(struct rw_semaphore *sem,
-                        unsigned int flags, signed long adjustment)
+                        enum rwsem_waiter_type type, signed long adjustment)
 {
        struct rwsem_waiter waiter;
        struct task_struct *tsk = current;
@@ -190,7 +193,7 @@ rwsem_down_failed_common(struct rw_semaphore *sem,
        /* set up my own style of waitqueue */
        raw_spin_lock_irq(&sem->wait_lock);
        waiter.task = tsk;
-       waiter.flags = flags;
+       waiter.type = type;
        get_task_struct(tsk);
 
        if (list_empty(&sem->wait_list))
@@ -221,7 +224,7 @@ rwsem_down_failed_common(struct rw_semaphore *sem,
 
                raw_spin_lock_irq(&sem->wait_lock);
                /* Try to get the writer sem, may steal from the head writer: */
-               if (flags == RWSEM_WAITING_FOR_WRITE)
+               if (type == RWSEM_WAITING_FOR_WRITE)
                        if (try_get_writer_sem(sem, &waiter)) {
                                raw_spin_unlock_irq(&sem->wait_lock);
                                return sem;