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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /arch/sh/kernel/semaphore.c
downloadlinux-stericsson-2.6.12-rc2.tar.gz
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
Diffstat (limited to 'arch/sh/kernel/semaphore.c')
-rw-r--r--arch/sh/kernel/semaphore.c139
1 files changed, 139 insertions, 0 deletions
diff --git a/arch/sh/kernel/semaphore.c b/arch/sh/kernel/semaphore.c
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+/*
+ * Just taken from alpha implementation.
+ * This can't work well, perhaps.
+ */
+/*
+ * Generic semaphore code. Buyer beware. Do your own
+ * specific changes in <asm/semaphore-helper.h>
+ */
+
+#include <linux/errno.h>
+#include <linux/sched.h>
+#include <linux/wait.h>
+#include <linux/init.h>
+#include <asm/semaphore.h>
+#include <asm/semaphore-helper.h>
+
+spinlock_t semaphore_wake_lock;
+
+/*
+ * 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.
+ */
+void __up(struct semaphore *sem)
+{
+ wake_one_more(sem);
+ wake_up(&sem->wait);
+}
+
+/*
+ * 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).
+ *
+ * Either form may be used in conjunction with "up()".
+ *
+ */
+
+#define DOWN_VAR \
+ struct task_struct *tsk = current; \
+ wait_queue_t wait; \
+ init_waitqueue_entry(&wait, tsk);
+
+#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. \
+ */ \
+ for (;;) {
+
+#define DOWN_TAIL(task_state) \
+ tsk->state = (task_state); \
+ } \
+ tsk->state = TASK_RUNNING; \
+ remove_wait_queue(&sem->wait, &wait);
+
+void __sched __down(struct semaphore * sem)
+{
+ DOWN_VAR
+ DOWN_HEAD(TASK_UNINTERRUPTIBLE)
+ if (waking_non_zero(sem))
+ break;
+ schedule();
+ DOWN_TAIL(TASK_UNINTERRUPTIBLE)
+}
+
+int __sched __down_interruptible(struct semaphore * sem)
+{
+ int ret = 0;
+ DOWN_VAR
+ DOWN_HEAD(TASK_INTERRUPTIBLE)
+
+ ret = waking_non_zero_interruptible(sem, tsk);
+ if (ret)
+ {
+ if (ret == 1)
+ /* ret != 0 only if we get interrupted -arca */
+ ret = 0;
+ break;
+ }
+ schedule();
+ DOWN_TAIL(TASK_INTERRUPTIBLE)
+ return ret;
+}
+
+int __down_trylock(struct semaphore * sem)
+{
+ return waking_non_zero_trylock(sem);
+}