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

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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>
This commit is contained in:
Michel Lespinasse 2013-05-07 06:45:49 -07:00 committed by Linus Torvalds
parent c1be5a5b1b
commit e2d57f782c
2 changed files with 24 additions and 18 deletions
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19
lib/rwsem-spinlock.c
View 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 */

23
lib/rwsem.c
View 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 @@ static int try_get_writer_sem(struct rw_semaphore *sem,
*/
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;