Revision c33880aaddbbab1ccf36f4457ed1090621f2e39a authored by Kirill Korotaev on 25 May 2005, 02:29:47 UTC, committed by Linus Torvalds on 25 May 2005, 03:08:13 UTC
If SIGKILL does not have priority, we cannot instantly kill task before it makes some unexpected job. It can be critical, but we were unable to reproduce this easily until Heiko Carstens <Heiko.Carstens@de.ibm.com> reported this problem on LKML. Signed-Off-By: Kirill Korotaev <dev@sw.ru> Signed-Off-By: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
1 parent 6431e6a
rwsem-spinlock.c
/* 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>
* - Derived also from comments by Linus
*/
#include <linux/rwsem.h>
#include <linux/sched.h>
#include <linux/module.h>
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
};
#if RWSEM_DEBUG
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);
}
#endif
/*
* initialise the semaphore
*/
void fastcall init_rwsem(struct rw_semaphore *sem)
{
sem->activity = 0;
spin_lock_init(&sem->wait_lock);
INIT_LIST_HEAD(&sem->wait_list);
#if RWSEM_DEBUG
sem->debug = 0;
#endif
}
/*
* 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
* - 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 wakewrite is non-zero
*/
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");
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
if (!wakewrite) {
if (waiter->flags & RWSEM_WAITING_FOR_WRITE)
goto out;
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 (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 */
smp_mb();
waiter->task = NULL;
wake_up_process(tsk);
put_task_struct(tsk);
goto out;
}
/* 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) {
struct list_head *next = waiter->list.next;
list_del(&waiter->list);
tsk = waiter->task;
smp_mb();
waiter->task = NULL;
wake_up_process(tsk);
put_task_struct(tsk);
woken++;
if (list_empty(&sem->wait_list))
break;
waiter = list_entry(next, struct rwsem_waiter, list);
}
sem->activity += woken;
out:
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)
{
struct rwsem_waiter *waiter;
struct task_struct *tsk;
sem->activity = -1;
waiter = list_entry(sem->wait_list.next, struct rwsem_waiter, list);
list_del(&waiter->list);
tsk = waiter->task;
smp_mb();
waiter->task = NULL;
wake_up_process(tsk);
put_task_struct(tsk);
return sem;
}
/*
* get a read lock on the semaphore
*/
void fastcall __sched __down_read(struct rw_semaphore *sem)
{
struct rwsem_waiter waiter;
struct task_struct *tsk;
rwsemtrace(sem, "Entering __down_read");
spin_lock_irq(&sem->wait_lock);
if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
/* granted */
sem->activity++;
spin_unlock_irq(&sem->wait_lock);
goto out;
}
tsk = current;
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);
/* we don't need to touch the semaphore struct anymore */
spin_unlock_irq(&sem->wait_lock);
/* wait to be given the lock */
for (;;) {
if (!waiter.task)
break;
schedule();
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
}
tsk->state = TASK_RUNNING;
out:
rwsemtrace(sem, "Leaving __down_read");
}
/*
* trylock for reading -- returns 1 if successful, 0 if contention
*/
int fastcall __down_read_trylock(struct rw_semaphore *sem)
{
unsigned long flags;
int ret = 0;
rwsemtrace(sem, "Entering __down_read_trylock");
spin_lock_irqsave(&sem->wait_lock, flags);
if (sem->activity >= 0 && list_empty(&sem->wait_list)) {
/* granted */
sem->activity++;
ret = 1;
}
spin_unlock_irqrestore(&sem->wait_lock, flags);
rwsemtrace(sem, "Leaving __down_read_trylock");
return ret;
}
/*
* get a write lock on the semaphore
* - we increment the waiting count anyway to indicate an exclusive lock
*/
void fastcall __sched __down_write(struct rw_semaphore *sem)
{
struct rwsem_waiter waiter;
struct task_struct *tsk;
rwsemtrace(sem, "Entering __down_write");
spin_lock_irq(&sem->wait_lock);
if (sem->activity == 0 && list_empty(&sem->wait_list)) {
/* granted */
sem->activity = -1;
spin_unlock_irq(&sem->wait_lock);
goto out;
}
tsk = current;
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);
/* we don't need to touch the semaphore struct anymore */
spin_unlock_irq(&sem->wait_lock);
/* wait to be given the lock */
for (;;) {
if (!waiter.task)
break;
schedule();
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
}
tsk->state = TASK_RUNNING;
out:
rwsemtrace(sem, "Leaving __down_write");
}
/*
* trylock for writing -- returns 1 if successful, 0 if contention
*/
int fastcall __down_write_trylock(struct rw_semaphore *sem)
{
unsigned long flags;
int ret = 0;
rwsemtrace(sem, "Entering __down_write_trylock");
spin_lock_irqsave(&sem->wait_lock, flags);
if (sem->activity == 0 && list_empty(&sem->wait_list)) {
/* granted */
sem->activity = -1;
ret = 1;
}
spin_unlock_irqrestore(&sem->wait_lock, flags);
rwsemtrace(sem, "Leaving __down_write_trylock");
return ret;
}
/*
* release a read lock on the semaphore
*/
void fastcall __up_read(struct rw_semaphore *sem)
{
unsigned long flags;
rwsemtrace(sem, "Entering __up_read");
spin_lock_irqsave(&sem->wait_lock, flags);
if (--sem->activity == 0 && !list_empty(&sem->wait_list))
sem = __rwsem_wake_one_writer(sem);
spin_unlock_irqrestore(&sem->wait_lock, flags);
rwsemtrace(sem, "Leaving __up_read");
}
/*
* release a write lock on the semaphore
*/
void fastcall __up_write(struct rw_semaphore *sem)
{
unsigned long flags;
rwsemtrace(sem, "Entering __up_write");
spin_lock_irqsave(&sem->wait_lock, flags);
sem->activity = 0;
if (!list_empty(&sem->wait_list))
sem = __rwsem_do_wake(sem, 1);
spin_unlock_irqrestore(&sem->wait_lock, flags);
rwsemtrace(sem, "Leaving __up_write");
}
/*
* downgrade a write lock into a read lock
* - just wake up any readers at the front of the queue
*/
void fastcall __downgrade_write(struct rw_semaphore *sem)
{
unsigned long flags;
rwsemtrace(sem, "Entering __downgrade_write");
spin_lock_irqsave(&sem->wait_lock, flags);
sem->activity = 1;
if (!list_empty(&sem->wait_list))
sem = __rwsem_do_wake(sem, 0);
spin_unlock_irqrestore(&sem->wait_lock, flags);
rwsemtrace(sem, "Leaving __downgrade_write");
}
EXPORT_SYMBOL(init_rwsem);
EXPORT_SYMBOL(__down_read);
EXPORT_SYMBOL(__down_read_trylock);
EXPORT_SYMBOL(__down_write);
EXPORT_SYMBOL(__down_write_trylock);
EXPORT_SYMBOL(__up_read);
EXPORT_SYMBOL(__up_write);
EXPORT_SYMBOL(__downgrade_write);
#if RWSEM_DEBUG
EXPORT_SYMBOL(rwsemtrace);
#endif
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