Generic semaphore implementation
Semaphores are no longer performance-critical, so a generic C implementation is better for maintainability, debuggability and extensibility. Thanks to Peter Zijlstra for fixing the lockdep warning. Thanks to Harvey Harrison for pointing out that the unlikely() was unnecessary. Signed-off-by: Matthew Wilcox <willy@linux.intel.com> Acked-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Matthew Wilcox
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Matthew Wilcox
Matthew Wilcox
parent
e48b3deee4
commit
64ac24e738
@@ -10,7 +10,7 @@ endif
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extra-y += vmlinux.lds
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obj-y := entry.o process.o traps.o ints.o signal.o ptrace.o module.o \
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sys_m68k.o time.o semaphore.o setup.o m68k_ksyms.o devres.o
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sys_m68k.o time.o setup.o m68k_ksyms.o devres.o
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devres-y = ../../../kernel/irq/devres.o
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@@ -1,5 +1,4 @@
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#include <linux/module.h>
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#include <asm/semaphore.h>
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asmlinkage long long __ashldi3 (long long, int);
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asmlinkage long long __ashrdi3 (long long, int);
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@@ -15,8 +14,3 @@ EXPORT_SYMBOL(__ashrdi3);
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EXPORT_SYMBOL(__lshrdi3);
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EXPORT_SYMBOL(__muldi3);
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EXPORT_SYMBOL(__down_failed);
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EXPORT_SYMBOL(__down_failed_interruptible);
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EXPORT_SYMBOL(__down_failed_trylock);
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EXPORT_SYMBOL(__up_wakeup);
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@@ -1,132 +0,0 @@
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/*
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* Generic semaphore code. Buyer beware. Do your own
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* specific changes in <asm/semaphore-helper.h>
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*/
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#include <linux/sched.h>
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#include <linux/init.h>
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#include <asm/semaphore-helper.h>
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#ifndef CONFIG_RMW_INSNS
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spinlock_t semaphore_wake_lock;
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#endif
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/*
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* Semaphores are implemented using a two-way counter:
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* The "count" variable is decremented for each process
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* that tries to sleep, while the "waking" variable is
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* incremented when the "up()" code goes to wake up waiting
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* processes.
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*
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* Notably, the inline "up()" and "down()" functions can
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* efficiently test if they need to do any extra work (up
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* needs to do something only if count was negative before
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* the increment operation.
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*
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* waking_non_zero() (from asm/semaphore.h) must execute
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* atomically.
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*
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* When __up() is called, the count was negative before
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* incrementing it, and we need to wake up somebody.
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*
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* This routine adds one to the count of processes that need to
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* wake up and exit. ALL waiting processes actually wake up but
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* only the one that gets to the "waking" field first will gate
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* through and acquire the semaphore. The others will go back
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* to sleep.
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*
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* Note that these functions are only called when there is
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* contention on the lock, and as such all this is the
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* "non-critical" part of the whole semaphore business. The
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* critical part is the inline stuff in <asm/semaphore.h>
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* where we want to avoid any extra jumps and calls.
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*/
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void __up(struct semaphore *sem)
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{
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wake_one_more(sem);
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wake_up(&sem->wait);
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}
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/*
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* Perform the "down" function. Return zero for semaphore acquired,
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* return negative for signalled out of the function.
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*
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* If called from __down, the return is ignored and the wait loop is
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* not interruptible. This means that a task waiting on a semaphore
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* using "down()" cannot be killed until someone does an "up()" on
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* the semaphore.
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*
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* If called from __down_interruptible, the return value gets checked
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* upon return. If the return value is negative then the task continues
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* with the negative value in the return register (it can be tested by
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* the caller).
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*
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* Either form may be used in conjunction with "up()".
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*
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*/
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#define DOWN_HEAD(task_state) \
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\
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\
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current->state = (task_state); \
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add_wait_queue(&sem->wait, &wait); \
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\
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/* \
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* Ok, we're set up. sem->count is known to be less than zero \
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* so we must wait. \
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* \
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* We can let go the lock for purposes of waiting. \
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* We re-acquire it after awaking so as to protect \
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* all semaphore operations. \
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* \
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* If "up()" is called before we call waking_non_zero() then \
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* we will catch it right away. If it is called later then \
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* we will have to go through a wakeup cycle to catch it. \
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* \
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* Multiple waiters contend for the semaphore lock to see \
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* who gets to gate through and who has to wait some more. \
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*/ \
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for (;;) {
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#define DOWN_TAIL(task_state) \
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current->state = (task_state); \
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} \
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current->state = TASK_RUNNING; \
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remove_wait_queue(&sem->wait, &wait);
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void __sched __down(struct semaphore * sem)
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{
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DECLARE_WAITQUEUE(wait, current);
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DOWN_HEAD(TASK_UNINTERRUPTIBLE)
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if (waking_non_zero(sem))
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break;
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schedule();
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DOWN_TAIL(TASK_UNINTERRUPTIBLE)
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}
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int __sched __down_interruptible(struct semaphore * sem)
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{
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DECLARE_WAITQUEUE(wait, current);
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int ret = 0;
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DOWN_HEAD(TASK_INTERRUPTIBLE)
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ret = waking_non_zero_interruptible(sem, current);
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if (ret)
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{
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if (ret == 1)
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/* ret != 0 only if we get interrupted -arca */
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ret = 0;
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break;
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}
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schedule();
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DOWN_TAIL(TASK_INTERRUPTIBLE)
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return ret;
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}
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int __down_trylock(struct semaphore * sem)
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{
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return waking_non_zero_trylock(sem);
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}
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@@ -5,4 +5,4 @@
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EXTRA_AFLAGS := -traditional
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lib-y := ashldi3.o ashrdi3.o lshrdi3.o muldi3.o \
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checksum.o string.o semaphore.o uaccess.o
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checksum.o string.o uaccess.o
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@@ -1,53 +0,0 @@
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/*
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* linux/arch/m68k/lib/semaphore.S
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*
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* Copyright (C) 1996 Linus Torvalds
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*
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* m68k version by Andreas Schwab
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*/
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#include <linux/linkage.h>
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#include <asm/semaphore.h>
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/*
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* The semaphore operations have a special calling sequence that
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* allow us to do a simpler in-line version of them. These routines
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* need to convert that sequence back into the C sequence when
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* there is contention on the semaphore.
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*/
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ENTRY(__down_failed)
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moveml %a0/%d0/%d1,-(%sp)
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movel %a1,-(%sp)
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jbsr __down
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movel (%sp)+,%a1
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moveml (%sp)+,%a0/%d0/%d1
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rts
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ENTRY(__down_failed_interruptible)
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movel %a0,-(%sp)
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movel %d1,-(%sp)
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movel %a1,-(%sp)
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jbsr __down_interruptible
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movel (%sp)+,%a1
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movel (%sp)+,%d1
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movel (%sp)+,%a0
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rts
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ENTRY(__down_failed_trylock)
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movel %a0,-(%sp)
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movel %d1,-(%sp)
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movel %a1,-(%sp)
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jbsr __down_trylock
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movel (%sp)+,%a1
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movel (%sp)+,%d1
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movel (%sp)+,%a0
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rts
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ENTRY(__up_wakeup)
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moveml %a0/%d0/%d1,-(%sp)
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movel %a1,-(%sp)
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jbsr __up
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movel (%sp)+,%a1
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moveml (%sp)+,%a0/%d0/%d1
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rts
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