patch-2.4.25 linux-2.4.25/arch/mips/kernel/semaphore.c

• Lines: 370
• Date: 2004-02-18 05:36:30.000000000 -0800
• Orig file: linux-2.4.24/arch/mips/kernel/semaphore.c
• Orig date: 2001-04-17 17:19:25.000000000 -0700

diff -urN linux-2.4.24/arch/mips/kernel/semaphore.c linux-2.4.25/arch/mips/kernel/semaphore.c
@@ -1,129 +1,272 @@
 /*
- *  Generic semaphore code. Buyer beware. Do your own
- * specific changes in <asm/semaphore-helper.h>
+ * Copyright (C) 1999, 2001, 02, 03 Ralf Baechle
+ *
+ * Heavily inspired by the Alpha implementation
  */
-
+#include <linux/config.h>
+#include <linux/errno.h>
+#include <linux/module.h>
 #include <linux/sched.h>
-#include <asm/semaphore-helper.h>
+
+#ifdef CONFIG_CPU_HAS_LLDSCD
+/*
+ * On machines without lld/scd we need a spinlock to make the manipulation of
+ * sem->count and sem->waking atomic.  Scalability isn't an issue because
+ * this lock is used on UP only so it's just an empty variable.
+ */
+spinlock_t semaphore_lock = SPIN_LOCK_UNLOCKED;
+
+EXPORT_SYMBOL(semaphore_lock);
+#endif
 
 /*
- * Semaphores are implemented using a two-way counter:
- * The "count" variable is decremented for each process
- * that tries to sleep, while the "waking" variable is
- * incremented when the "up()" code goes to wake up waiting
- * processes.
- *
- * Notably, the inline "up()" and "down()" functions can
- * efficiently test if they need to do any extra work (up
- * needs to do something only if count was negative before
- * the increment operation.
- *
- * waking_non_zero() (from asm/semaphore.h) must execute
- * atomically.
- *
- * When __up() is called, the count was negative before
- * incrementing it, and we need to wake up somebody.
- *
- * This routine adds one to the count of processes that need to
- * wake up and exit.  ALL waiting processes actually wake up but
- * only the one that gets to the "waking" field first will gate
- * through and acquire the semaphore.  The others will go back
- * to sleep.
- *
- * Note that these functions are only called when there is
- * contention on the lock, and as such all this is the
- * "non-critical" part of the whole semaphore business. The
- * critical part is the inline stuff in <asm/semaphore.h>
- * where we want to avoid any extra jumps and calls.
+ * Semaphores are implemented using a two-way counter: The "count" variable is
+ * decremented for each process that tries to sleep, while the "waking" variable
+ * is incremented when the "up()" code goes to wake up waiting processes.
+ *
+ * Notably, the inline "up()" and "down()" functions can efficiently test if
+ * they need to do any extra work (up needs to do something only if count was
+ * negative before the increment operation.
+ *
+ * waking_non_zero() must execute atomically.
+ *
+ * When __up() is called, the count was negative before incrementing it, and we
+ * need to wake up somebody.
+ *
+ * This routine adds one to the count of processes that need to wake up and
+ * exit.  ALL waiting processes actually wake up but only the one that gets to
+ * the "waking" field first will gate through and acquire the semaphore.  The
+ * others will go back to sleep.
+ *
+ * Note that these functions are only called when there is contention on the
+ * lock, and as such all this is the "non-critical" part of the whole semaphore
+ * business. The critical part is the inline stuff in <asm/semaphore.h> where
+ * we want to avoid any extra jumps and calls.
  */
-void __up(struct semaphore *sem)
+void __up_wakeup(struct semaphore *sem)
 {
-	wake_one_more(sem);
 	wake_up(&sem->wait);
 }
 
+EXPORT_SYMBOL(__up_wakeup);
+
+#ifdef CONFIG_CPU_HAS_LLSC
+
+static inline int waking_non_zero(struct semaphore *sem)
+{
+	int ret, tmp;
+
+	__asm__ __volatile__(
+	"1:	ll	%1, %2			# waking_non_zero	\n"
+	"	blez	%1, 2f						\n"
+	"	subu	%0, %1, 1					\n"
+	"	sc	%0, %2						\n"
+	"	beqz	%0, 1b						\n"
+	"2:								\n"
+	: "=r" (ret), "=r" (tmp), "+m" (sem->waking)
+	: "0" (0));
+
+	return ret;
+}
+
+#else /* !CONFIG_CPU_HAS_LLSC */
+
+static inline int waking_non_zero(struct semaphore *sem)
+{
+	unsigned long flags;
+	int waking, ret = 0;
+
+	spin_lock_irqsave(&semaphore_lock, flags);
+	waking = atomic_read(&sem->waking);
+	if (waking > 0) {
+		atomic_set(&sem->waking, waking - 1);
+		ret = 1;
+	}
+	spin_unlock_irqrestore(&semaphore_lock, flags);
+
+	return ret;
+}
+
+#endif /* !CONFIG_CPU_HAS_LLSC */
+
 /*
- * Perform the "down" function.  Return zero for semaphore acquired,
- * return negative for signalled out of the function.
+ * Perform the "down" function.  Return zero for semaphore acquired, return
+ * negative for signalled out of the function.
  *
- * If called from __down, the return is ignored and the wait loop is
- * not interruptible.  This means that a task waiting on a semaphore
- * using "down()" cannot be killed until someone does an "up()" on
- * the semaphore.
- *
- * If called from __down_interruptible, the return value gets checked
- * upon return.  If the return value is negative then the task continues
- * with the negative value in the return register (it can be tested by
- * the caller).
+ * If called from down, the return is ignored and the wait loop is not
+ * interruptible.  This means that a task waiting on a semaphore using "down()"
+ * cannot be killed until someone does an "up()" on the semaphore.
  *
- * Either form may be used in conjunction with "up()".
+ * If called from down_interruptible, the return value gets checked upon return.
+ * If the return value is negative then the task continues with the negative
+ * value in the return register (it can be tested by the caller).
  *
+ * Either form may be used in conjunction with "up()".
  */
 
-#define DOWN_VAR				\
-	struct task_struct *tsk = current;	\
-	wait_queue_t wait;			\
+void __down_failed(struct semaphore * sem)
+{
+	struct task_struct *tsk = current;
+	wait_queue_t wait;
+
 	init_waitqueue_entry(&wait, tsk);
+	__set_current_state(TASK_UNINTERRUPTIBLE);
+	add_wait_queue_exclusive(&sem->wait, &wait);
 
-#define DOWN_HEAD(task_state)						\
-									\
-									\
-	tsk->state = (task_state);					\
-	add_wait_queue(&sem->wait, &wait);				\
-									\
-	/*								\
-	 * Ok, we're set up.  sem->count is known to be less than zero	\
-	 * so we must wait.						\
-	 *								\
-	 * We can let go the lock for purposes of waiting.		\
-	 * We re-acquire it after awaking so as to protect		\
-	 * all semaphore operations.					\
-	 *								\
-	 * If "up()" is called before we call waking_non_zero() then	\
-	 * we will catch it right away.  If it is called later then	\
-	 * we will have to go through a wakeup cycle to catch it.	\
-	 *								\
-	 * Multiple waiters contend for the semaphore lock to see	\
-	 * who gets to gate through and who has to wait some more.	\
-	 */								\
+	/*
+	 * Ok, we're set up.  sem->count is known to be less than zero
+	 * so we must wait.
+	 *
+	 * We can let go the lock for purposes of waiting.
+	 * We re-acquire it after awaking so as to protect
+	 * all semaphore operations.
+	 *
+	 * If "up()" is called before we call waking_non_zero() then
+	 * we will catch it right away.  If it is called later then
+	 * we will have to go through a wakeup cycle to catch it.
+	 *
+	 * Multiple waiters contend for the semaphore lock to see
+	 * who gets to gate through and who has to wait some more.
+	 */
 	for (;;) {
-
-#define DOWN_TAIL(task_state)			\
-		tsk->state = (task_state);	\
-	}					\
-	tsk->state = TASK_RUNNING;		\
+		if (waking_non_zero(sem))
+			break;
+		schedule();
+		__set_current_state(TASK_UNINTERRUPTIBLE);
+	}
+	__set_current_state(TASK_RUNNING);
 	remove_wait_queue(&sem->wait, &wait);
+}
+
+EXPORT_SYMBOL(__down_failed);
+
+#ifdef CONFIG_CPU_HAS_LLDSCD
+
+/*
+ * waking_non_zero_interruptible:
+ *	1	got the lock
+ *	0	go to sleep
+ *	-EINTR	interrupted
+ *
+ * We must undo the sem->count down_interruptible decrement
+ * simultaneously and atomically with the sem->waking adjustment,
+ * otherwise we can race with wake_one_more.
+ *
+ * This is accomplished by doing a 64-bit lld/scd on the 2 32-bit words.
+ *
+ * This is crazy.  Normally it's strictly forbidden to use 64-bit operations
+ * in the 32-bit MIPS kernel.  In this case it's however ok because if an
+ * interrupt has destroyed the upper half of registers sc will fail.
+ * Note also that this will not work for MIPS32 CPUs!
+ *
+ * Pseudocode:
+ *
+ * If(sem->waking > 0) {
+ *	Decrement(sem->waking)
+ *	Return(SUCCESS)
+ * } else If(signal_pending(tsk)) {
+ *	Increment(sem->count)
+ *	Return(-EINTR)
+ * } else {
+ *	Return(SLEEP)
+ * }
+ */
 
-void __down(struct semaphore * sem)
+static inline int
+waking_non_zero_interruptible(struct semaphore *sem, struct task_struct *tsk)
 {
-	DOWN_VAR
-	DOWN_HEAD(TASK_UNINTERRUPTIBLE)
-	if (waking_non_zero(sem))
-		break;
-	schedule();
-	DOWN_TAIL(TASK_UNINTERRUPTIBLE)
+	long ret, tmp;
+
+	__asm__ __volatile__(
+	"	.set	push		# waking_non_zero_interruptible	\n"
+	"	.set	mips3						\n"
+	"	.set	noat						\n"
+	"0:	lld	%1, %2						\n"
+	"	li	%0, 0						\n"
+	"	sll	$1, %1, 0					\n"
+	"	blez	$1, 1f						\n"
+	"	daddiu	%1, %1, -1					\n"
+	"	li	%0, 1						\n"
+	"	b	2f						\n"
+	"1:	beqz	%3, 2f						\n"
+	"	li	%0, %4						\n"
+	"	dli	$1, 0x0000000100000000				\n"
+	"	daddu	%1, %1, $1					\n"
+	"2:	scd	%1, %2						\n"
+	"	beqz	%1, 0b						\n"
+	"	.set	pop						\n"
+	: "=&r" (ret), "=&r" (tmp), "=m" (*sem)
+	: "r" (signal_pending(tsk)), "i" (-EINTR));
+
+	return ret;
 }
 
-int __down_interruptible(struct semaphore * sem)
+#else /* !CONFIG_CPU_HAS_LLDSCD */
+
+static inline int waking_non_zero_interruptible(struct semaphore *sem,
+						struct task_struct *tsk)
 {
-	int ret = 0;
-	DOWN_VAR
-	DOWN_HEAD(TASK_INTERRUPTIBLE)
+	int waking, pending, ret = 0;
+	unsigned long flags;
 
-	ret = waking_non_zero_interruptible(sem, tsk);
-	if (ret)
-	{
-		if (ret == 1)
-			/* ret != 0 only if we get interrupted -arca */
-			ret = 0;
-		break;
+	pending = signal_pending(tsk);
+
+	spin_lock_irqsave(&semaphore_lock, flags);
+	waking = atomic_read(&sem->waking);
+	if (waking > 0) {
+		atomic_set(&sem->waking, waking - 1);
+		ret = 1;
+	} else if (pending) {
+		atomic_set(&sem->count, atomic_read(&sem->count) + 1);
+		ret = -EINTR;
 	}
-	schedule();
-	DOWN_TAIL(TASK_INTERRUPTIBLE)
+	spin_unlock_irqrestore(&semaphore_lock, flags);
+
 	return ret;
 }
 
-int __down_trylock(struct semaphore * sem)
+#endif /* !CONFIG_CPU_HAS_LLDSCD */
+
+int __down_failed_interruptible(struct semaphore * sem)
 {
-	return waking_non_zero_trylock(sem);
+	struct task_struct *tsk = current;
+	wait_queue_t wait;
+	int ret = 0;
+
+	init_waitqueue_entry(&wait, tsk);
+	__set_current_state(TASK_INTERRUPTIBLE);
+	add_wait_queue_exclusive(&sem->wait, &wait);
+
+	/*
+	 * Ok, we're set up.  sem->count is known to be less than zero
+	 * so we must wait.
+	 *
+	 * We can let go the lock for purposes of waiting.
+	 * We re-acquire it after awaking so as to protect
+	 * all semaphore operations.
+	 *
+	 * If "up()" is called before we call waking_non_zero() then
+	 * we will catch it right away.  If it is called later then
+	 * we will have to go through a wakeup cycle to catch it.
+	 *
+	 * Multiple waiters contend for the semaphore lock to see
+	 * who gets to gate through and who has to wait some more.
+	 */
+	for (;;) {
+		ret = waking_non_zero_interruptible(sem, tsk);
+		if (ret) {
+			if (ret == 1)
+				/* ret != 0 only if we get interrupted -arca */
+				ret = 0;
+			break;
+		}
+		schedule();
+		__set_current_state(TASK_INTERRUPTIBLE);
+	}
+	__set_current_state(TASK_RUNNING);
+	remove_wait_queue(&sem->wait, &wait);
+
+	return ret;
 }
+
+EXPORT_SYMBOL(__down_failed_interruptible);