rwsem: make the waiter type an enumeration rather than a bitmask

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>

2 files changed, 24 insertions, 18 deletions

diff --git a/lib/rwsem-spinlock.c b/lib/rwsem-spinlock.c
index 7542afbb22b3..5f117f37ac0a 100644
--- a/lib/rwsem-spinlock.c
+++ b/lib/rwsem-spinlock.c
@@ -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 */
diff --git a/lib/rwsem.c b/lib/rwsem.c
index ad5e0df16ab4..672eb33218ac 100644
--- a/lib/rwsem.c
+++ b/lib/rwsem.c
@@ -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;