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Date: Wed, 6 Mar 2013 15:21:40 -0800
From: Michel Lespinasse <walken@...gle.com>
To: Alex Shi <alex.shi@...el.com>, Ingo Molnar <mingo@...nel.org>,
David Howells <dhowells@...hat.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Thomas Gleixner <tglx@...utronix.de>,
Yuanhan Liu <yuanhan.liu@...ux.intel.com>,
Rik van Riel <riel@...hat.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org
Subject: [PATCH 01/12] 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@...gle.com>
---
lib/rwsem-spinlock.c | 19 +++++++++++--------
lib/rwsem.c | 23 +++++++++++++----------
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;
--
1.8.1.3
--
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