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Commit 5136bab9 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
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[PATCH] lindent rwsem 

Lindent rwsem.c and rwsem-spinlock.c and fix a few things by hand.  Also
added a couple of comments for the memory barriers.  Added the __sched
annotation that was left out of rwsem-spinlock.c.
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 099bb7c0
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Showing with 110 additions and 96 deletions
lib/rwsem-spinlock.c
View file @ 5136bab9
/* rwsem-spinlock.c: R/W semaphores: contention handling functions for generic spinlock
* implementation
/* rwsem-spinlock.c: R/W semaphores: contention handling functions for
* generic spinlock implementation
*
* Copyright (c) 2001 David Howells (dhowells@redhat.com).
* - Derived partially from idea by Andrea Arcangeli <andrea@suse.de>
......@@ -22,7 +22,8 @@ void rwsemtrace(struct rw_semaphore *sem, const char *str)
{
if (sem->debug)
printk("[%d] %s({%d,%d})\n",
current->pid,str,sem->activity,list_empty(&sem->wait_list)?0:1);
current->pid, str, sem->activity,
list_empty(&sem->wait_list) ? 0 : 1);
}
#endif
......@@ -40,7 +41,7 @@ void fastcall init_rwsem(struct rw_semaphore *sem)
}
/*
* handle the lock being released whilst there are processes blocked on it that can now run
* handle the lock release when processes blocked on it that can now run
* - if we come here, then:
* - the 'active count' _reached_ zero
* - the 'waiting count' is non-zero
......@@ -48,15 +49,16 @@ void fastcall init_rwsem(struct rw_semaphore *sem)
* - woken process blocks are discarded from the list after having task zeroed
* - writers are only woken if wakewrite is non-zero
*/
static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
static inline struct rw_semaphore *
__rwsem_do_wake(struct rw_semaphore *sem, int wakewrite)
{
struct rwsem_waiter *waiter;
struct task_struct *tsk;
int woken;
rwsemtrace(sem,"Entering __rwsem_do_wake");
rwsemtrace(sem, "Entering __rwsem_do_wake");
waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list);
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
if (!wakewrite) {
if (waiter->flags & RWSEM_WAITING_FOR_WRITE)
......@@ -64,14 +66,16 @@ static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int
goto dont_wake_writers;
}
/* if we are allowed to wake writers try to grant a single write lock if there's a
* writer at the front of the queue
* - we leave the 'waiting count' incremented to signify potential contention
/* if we are allowed to wake writers try to grant a single write lock
* if there's a writer at the front of the queue
* - we leave the 'waiting count' incremented to signify potential
* contention
*/
if (waiter->flags & RWSEM_WAITING_FOR_WRITE) {
sem->activity = -1;
list_del(&waiter->list);
tsk = waiter->task;
/* Don't touch waiter after ->task has been NULLed */
mb();
waiter->task = NULL;
wake_up_process(tsk);
......@@ -79,10 +83,10 @@ static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int
goto out;
}
/* grant an infinite number of read locks to the readers at the front of the queue */
/* 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->flags & RWSEM_WAITING_FOR_READ) {
struct list_head *next = waiter->list.next;
list_del(&waiter->list);
......@@ -94,27 +98,28 @@ static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int
woken++;
if (list_empty(&sem->wait_list))
break;
waiter = list_entry(next,struct rwsem_waiter,list);
waiter = list_entry(next, struct rwsem_waiter, list);
}
sem->activity += woken;
out:
rwsemtrace(sem,"Leaving __rwsem_do_wake");
rwsemtrace(sem, "Leaving __rwsem_do_wake");
return sem;
}
/*
* wake a single writer
*/
static inline struct rw_semaphore *__rwsem_wake_one_writer(struct rw_semaphore *sem)
static inline struct rw_semaphore *
__rwsem_wake_one_writer(struct rw_semaphore *sem)
{
struct rwsem_waiter *waiter;
struct task_struct *tsk;
sem->activity = -1;
waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list);
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
list_del(&waiter->list);
tsk = waiter->task;
......@@ -128,16 +133,16 @@ static inline struct rw_semaphore *__rwsem_wake_one_writer(struct rw_semaphore *
/*
* get a read lock on the semaphore
*/
void fastcall __down_read(struct rw_semaphore *sem)
void fastcall __sched __down_read(struct rw_semaphore *sem)
{
struct rwsem_waiter waiter;
struct task_struct *tsk;
rwsemtrace(sem,"Entering __down_read");
rwsemtrace(sem, "Entering __down_read");
spin_lock(&sem->wait_lock);
if (sem->activity>=0 && list_empty(&sem->wait_list)) {
if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
/* granted */
sem->activity++;
spin_unlock(&sem->wait_lock);
......@@ -145,14 +150,14 @@ void fastcall __down_read(struct rw_semaphore *sem)
}
tsk = current;
set_task_state(tsk,TASK_UNINTERRUPTIBLE);
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
/* set up my own style of waitqueue */
waiter.task = tsk;
waiter.flags = RWSEM_WAITING_FOR_READ;
get_task_struct(tsk);
list_add_tail(&waiter.list,&sem->wait_list);
list_add_tail(&waiter.list, &sem->wait_list);
/* we don't need to touch the semaphore struct anymore */
spin_unlock(&sem->wait_lock);
......@@ -168,7 +173,7 @@ void fastcall __down_read(struct rw_semaphore *sem)
tsk->state = TASK_RUNNING;
out:
rwsemtrace(sem,"Leaving __down_read");
rwsemtrace(sem, "Leaving __down_read");
}
/*
......@@ -177,11 +182,11 @@ void fastcall __down_read(struct rw_semaphore *sem)
int fastcall __down_read_trylock(struct rw_semaphore *sem)
{
int ret = 0;
rwsemtrace(sem,"Entering __down_read_trylock");
rwsemtrace(sem, "Entering __down_read_trylock");
spin_lock(&sem->wait_lock);
if (sem->activity>=0 && list_empty(&sem->wait_list)) {
if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
/* granted */
sem->activity++;
ret = 1;
......@@ -189,24 +194,24 @@ int fastcall __down_read_trylock(struct rw_semaphore *sem)
spin_unlock(&sem->wait_lock);
rwsemtrace(sem,"Leaving __down_read_trylock");
rwsemtrace(sem, "Leaving __down_read_trylock");
return ret;
}
/*
* get a write lock on the semaphore
* - note that we increment the waiting count anyway to indicate an exclusive lock
* - we increment the waiting count anyway to indicate an exclusive lock
*/
void fastcall __down_write(struct rw_semaphore *sem)
void fastcall __sched __down_write(struct rw_semaphore *sem)
{
struct rwsem_waiter waiter;
struct task_struct *tsk;
rwsemtrace(sem,"Entering __down_write");
rwsemtrace(sem, "Entering __down_write");
spin_lock(&sem->wait_lock);
if (sem->activity==0 && list_empty(&sem->wait_list)) {
if (sem->activity == 0 && list_empty(&sem->wait_list)) {
/* granted */
sem->activity = -1;
spin_unlock(&sem->wait_lock);
......@@ -214,14 +219,14 @@ void fastcall __down_write(struct rw_semaphore *sem)
}
tsk = current;
set_task_state(tsk,TASK_UNINTERRUPTIBLE);
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
/* set up my own style of waitqueue */
waiter.task = tsk;
waiter.flags = RWSEM_WAITING_FOR_WRITE;
get_task_struct(tsk);
list_add_tail(&waiter.list,&sem->wait_list);
list_add_tail(&waiter.list, &sem->wait_list);
/* we don't need to touch the semaphore struct anymore */
spin_unlock(&sem->wait_lock);
......@@ -237,7 +242,7 @@ void fastcall __down_write(struct rw_semaphore *sem)
tsk->state = TASK_RUNNING;
out:
rwsemtrace(sem,"Leaving __down_write");
rwsemtrace(sem, "Leaving __down_write");
}
/*
......@@ -246,11 +251,11 @@ void fastcall __down_write(struct rw_semaphore *sem)
int fastcall __down_write_trylock(struct rw_semaphore *sem)
{
int ret = 0;
rwsemtrace(sem,"Entering __down_write_trylock");
rwsemtrace(sem, "Entering __down_write_trylock");
spin_lock(&sem->wait_lock);
if (sem->activity==0 && list_empty(&sem->wait_list)) {
if (sem->activity == 0 && list_empty(&sem->wait_list)) {
/* granted */
sem->activity = -1;
ret = 1;
......@@ -258,7 +263,7 @@ int fastcall __down_write_trylock(struct rw_semaphore *sem)
spin_unlock(&sem->wait_lock);
rwsemtrace(sem,"Leaving __down_write_trylock");
rwsemtrace(sem, "Leaving __down_write_trylock");
return ret;
}
......@@ -267,16 +272,16 @@ int fastcall __down_write_trylock(struct rw_semaphore *sem)
*/
void fastcall __up_read(struct rw_semaphore *sem)
{
rwsemtrace(sem,"Entering __up_read");
rwsemtrace(sem, "Entering __up_read");
spin_lock(&sem->wait_lock);
if (--sem->activity==0 && !list_empty(&sem->wait_list))
if (--sem->activity == 0 && !list_empty(&sem->wait_list))
sem = __rwsem_wake_one_writer(sem);
spin_unlock(&sem->wait_lock);
rwsemtrace(sem,"Leaving __up_read");
rwsemtrace(sem, "Leaving __up_read");
}
/*
......@@ -284,7 +289,7 @@ void fastcall __up_read(struct rw_semaphore *sem)
*/
void fastcall __up_write(struct rw_semaphore *sem)
{
rwsemtrace(sem,"Entering __up_write");
rwsemtrace(sem, "Entering __up_write");
spin_lock(&sem->wait_lock);
......@@ -294,7 +299,7 @@ void fastcall __up_write(struct rw_semaphore *sem)
spin_unlock(&sem->wait_lock);
rwsemtrace(sem,"Leaving __up_write");
rwsemtrace(sem, "Leaving __up_write");
}
/*
......@@ -303,17 +308,17 @@ void fastcall __up_write(struct rw_semaphore *sem)
*/
void fastcall __downgrade_write(struct rw_semaphore *sem)
{
rwsemtrace(sem,"Entering __downgrade_write");
rwsemtrace(sem, "Entering __downgrade_write");
spin_lock(&sem->wait_lock);
sem->activity = 1;
if (!list_empty(&sem->wait_list))
sem = __rwsem_do_wake(sem,0);
sem = __rwsem_do_wake(sem, 0);
spin_unlock(&sem->wait_lock);
rwsemtrace(sem,"Leaving __downgrade_write");
rwsemtrace(sem, "Leaving __downgrade_write");
}
EXPORT_SYMBOL(init_rwsem);
......
lib/rwsem.c
View file @ 5136bab9
......@@ -20,31 +20,32 @@ struct rwsem_waiter {
#undef rwsemtrace
void rwsemtrace(struct rw_semaphore *sem, const char *str)
{
printk("sem=%p\n",sem);
printk("(sem)=%08lx\n",sem->count);
printk("sem=%p\n", sem);
printk("(sem)=%08lx\n", sem->count);
if (sem->debug)
printk("[%d] %s({%08lx})\n",current->pid,str,sem->count);
printk("[%d] %s({%08lx})\n", current->pid, str, sem->count);
}
#endif
/*
* handle the lock being released whilst there are processes blocked on it that can now run
* handle the lock release when processes blocked on it that can now run
* - if we come here from up_xxxx(), then:
* - the 'active part' of the count (&0x0000ffff) had reached zero (but may have changed)
* - the 'waiting part' of the count (&0xffff0000) is negative (and will still be so)
* - the 'active part' of count (&0x0000ffff) reached 0 (but may have changed)
* - the 'waiting part' of count (&0xffff0000) is -ve (and will still be so)
* - there must be someone on the queue
* - the spinlock must be held by the caller
* - woken process blocks are discarded from the list after having task zeroed
* - writers are only woken if downgrading is false
*/
static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int downgrading)
static inline struct rw_semaphore *
__rwsem_do_wake(struct rw_semaphore *sem, int downgrading)
{
struct rwsem_waiter *waiter;
struct task_struct *tsk;
struct list_head *next;
signed long oldcount, woken, loop;
rwsemtrace(sem,"Entering __rwsem_do_wake");
rwsemtrace(sem, "Entering __rwsem_do_wake");
if (downgrading)
goto dont_wake_writers;
......@@ -53,19 +54,24 @@ static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int
* if we can transition the active part of the count from 0 -> 1
*/
try_again:
oldcount = rwsem_atomic_update(RWSEM_ACTIVE_BIAS,sem) - RWSEM_ACTIVE_BIAS;
oldcount = rwsem_atomic_update(RWSEM_ACTIVE_BIAS, sem)
- RWSEM_ACTIVE_BIAS;
if (oldcount & RWSEM_ACTIVE_MASK)
goto undo;
waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list);
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
/* try to grant a single write lock if there's a writer at the front of the queue
* - note we leave the 'active part' of the count incremented by 1 and the waiting part
* incremented by 0x00010000
/* try to grant a single write lock if there's a writer at the front
* of the queue - note we leave the 'active part' of the count
* incremented by 1 and the waiting part incremented by 0x00010000
*/
if (!(waiter->flags & RWSEM_WAITING_FOR_WRITE))
goto readers_only;
/* We must be careful not to touch 'waiter' after we set ->task = NULL.
* It is an allocated on the waiter's stack and may become invalid at
* any time after that point (due to a wakeup from another source).
*/
list_del(&waiter->list);
tsk = waiter->task;
mb();
......@@ -76,7 +82,7 @@ static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int
/* don't want to wake any writers */
dont_wake_writers:
waiter = list_entry(sem->wait_list.next,struct rwsem_waiter,list);
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
if (waiter->flags & RWSEM_WAITING_FOR_WRITE)
goto out;
......@@ -90,23 +96,25 @@ static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int
do {
woken++;
if (waiter->list.next==&sem->wait_list)
if (waiter->list.next == &sem->wait_list)
break;
waiter = list_entry(waiter->list.next,struct rwsem_waiter,list);
waiter = list_entry(waiter->list.next,
struct rwsem_waiter, list);
} while (waiter->flags & RWSEM_WAITING_FOR_READ);
loop = woken;
woken *= RWSEM_ACTIVE_BIAS - RWSEM_WAITING_BIAS;
if (!downgrading)
woken -= RWSEM_ACTIVE_BIAS; /* we'd already done one increment
* earlier */
rwsem_atomic_add(woken,sem);
/* we'd already done one increment earlier */
woken -= RWSEM_ACTIVE_BIAS;
rwsem_atomic_add(woken, sem);
next = sem->wait_list.next;
for (; loop>0; loop--) {
waiter = list_entry(next,struct rwsem_waiter,list);
for (; loop > 0; loop--) {
waiter = list_entry(next, struct rwsem_waiter, list);
next = waiter->list.next;
tsk = waiter->task;
mb();
......@@ -119,12 +127,12 @@ static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int
next->prev = &sem->wait_list;
out:
rwsemtrace(sem,"Leaving __rwsem_do_wake");
rwsemtrace(sem, "Leaving __rwsem_do_wake");
return sem;
/* undo the change to count, but check for a transition 1->0 */
undo:
if (rwsem_atomic_update(-RWSEM_ACTIVE_BIAS,sem)!=0)
if (rwsem_atomic_update(-RWSEM_ACTIVE_BIAS, sem) != 0)
goto out;
goto try_again;
}
......@@ -132,28 +140,26 @@ static inline struct rw_semaphore *__rwsem_do_wake(struct rw_semaphore *sem, int
/*
* wait for a lock to be granted
*/
static inline struct rw_semaphore *rwsem_down_failed_common(struct rw_semaphore *sem,
struct rwsem_waiter *waiter,
signed long adjustment)
static inline struct rw_semaphore *
rwsem_down_failed_common(struct rw_semaphore *sem,
struct rwsem_waiter *waiter, signed long adjustment)
{
struct task_struct *tsk = current;
signed long count;
set_task_state(tsk,TASK_UNINTERRUPTIBLE);
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
/* set up my own style of waitqueue */
spin_lock(&sem->wait_lock);
waiter->task = tsk;
get_task_struct(tsk);
list_add_tail(&waiter->list,&sem->wait_list);
list_add_tail(&waiter->list, &sem->wait_list);
/* note that we're now waiting on the lock, but no longer actively read-locking */
count = rwsem_atomic_update(adjustment,sem);
/* we're now waiting on the lock, but no longer actively read-locking */
count = rwsem_atomic_update(adjustment, sem);
/* if there are no longer active locks, wake the front queued process(es) up
* - it might even be this process, since the waker takes a more active part
*/
/* if there are no active locks, wake the front queued process(es) up */
if (!(count & RWSEM_ACTIVE_MASK))
sem = __rwsem_do_wake(sem, 0);
......@@ -175,42 +181,45 @@ static inline struct rw_semaphore *rwsem_down_failed_common(struct rw_semaphore
/*
* wait for the read lock to be granted
*/
struct rw_semaphore fastcall __sched *rwsem_down_read_failed(struct rw_semaphore *sem)
struct rw_semaphore fastcall __sched *
rwsem_down_read_failed(struct rw_semaphore *sem)
{
struct rwsem_waiter waiter;
rwsemtrace(sem,"Entering rwsem_down_read_failed");
rwsemtrace(sem, "Entering rwsem_down_read_failed");
waiter.flags = RWSEM_WAITING_FOR_READ;
rwsem_down_failed_common(sem,&waiter,RWSEM_WAITING_BIAS-RWSEM_ACTIVE_BIAS);
rwsem_down_failed_common(sem, &waiter,
RWSEM_WAITING_BIAS - RWSEM_ACTIVE_BIAS);
rwsemtrace(sem,"Leaving rwsem_down_read_failed");
rwsemtrace(sem, "Leaving rwsem_down_read_failed");
return sem;
}
/*
* wait for the write lock to be granted
*/
struct rw_semaphore fastcall __sched *rwsem_down_write_failed(struct rw_semaphore *sem)
struct rw_semaphore fastcall __sched *
rwsem_down_write_failed(struct rw_semaphore *sem)
{
struct rwsem_waiter waiter;
rwsemtrace(sem,"Entering rwsem_down_write_failed");
rwsemtrace(sem, "Entering rwsem_down_write_failed");
waiter.flags = RWSEM_WAITING_FOR_WRITE;
rwsem_down_failed_common(sem,&waiter,-RWSEM_ACTIVE_BIAS);
rwsem_down_failed_common(sem, &waiter, -RWSEM_ACTIVE_BIAS);
rwsemtrace(sem,"Leaving rwsem_down_write_failed");
rwsemtrace(sem, "Leaving rwsem_down_write_failed");
return sem;
}
/*
* handle waking up a waiter on the semaphore
* - up_read/up_write has decremented the active part of the count if we come here
* - up_read/up_write has decremented the active part of count if we come here
*/
struct rw_semaphore fastcall *rwsem_wake(struct rw_semaphore *sem)
{
rwsemtrace(sem,"Entering rwsem_wake");
rwsemtrace(sem, "Entering rwsem_wake");
spin_lock(&sem->wait_lock);
......@@ -220,19 +229,19 @@ struct rw_semaphore fastcall *rwsem_wake(struct rw_semaphore *sem)
spin_unlock(&sem->wait_lock);
rwsemtrace(sem,"Leaving rwsem_wake");
rwsemtrace(sem, "Leaving rwsem_wake");
return sem;
}
/*
* downgrade a write lock into a read lock
* - caller incremented waiting part of count, and discovered it to be still negative
* - caller incremented waiting part of count and discovered it still negative
* - just wake up any readers at the front of the queue
*/
struct rw_semaphore fastcall *rwsem_downgrade_wake(struct rw_semaphore *sem)
{
rwsemtrace(sem,"Entering rwsem_downgrade_wake");
rwsemtrace(sem, "Entering rwsem_downgrade_wake");
spin_lock(&sem->wait_lock);
......@@ -242,7 +251,7 @@ struct rw_semaphore fastcall *rwsem_downgrade_wake(struct rw_semaphore *sem)
spin_unlock(&sem->wait_lock);
rwsemtrace(sem,"Leaving rwsem_downgrade_wake");
rwsemtrace(sem, "Leaving rwsem_downgrade_wake");
return sem;
}
......
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