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Commit 5b9c5a1c authored by Michel Lespinasse's avatar Michel Lespinasse Committed by Samuel Pascua
Browse files

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

this is patch 1/12: https://lkml.org/lkml/2013/3/6/566



found this patch series commited by faux123.

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.

Change-Id: I45669f17017a82f666af3be9392179e567f462fa
Signed-off-by: default avatarMichel Lespinasse <walken@google.com>
parent 24a950e4

lib/rwsem-spinlock.c

+11 −8
Original line number Diff line number Diff line
@@ -9,12 +9,15 @@ 
#include <linux/sched.h>

#include <linux/module.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 */

lib/rwsem.c

+13 −10
Original line number Diff line number Diff line
@@ -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;