path: root/sys/kern/kern_lock.c

/*	$OpenBSD: kern_lock.c,v 1.35 2010/04/26 05:48:17 deraadt Exp $	*/

/* 
 * Copyright (c) 1995
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code contains ideas from software contributed to Berkeley by
 * Avadis Tevanian, Jr., Michael Wayne Young, and the Mach Operating
 * System project at Carnegie-Mellon University.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)kern_lock.c	8.18 (Berkeley) 5/21/95
 */

#include <sys/param.h>
#include <sys/proc.h>
#include <sys/lock.h>
#include <sys/systm.h>
#include <sys/sched.h>

#include <machine/cpu.h>

/*
 * Locking primitives implementation.
 * Locks provide shared/exclusive synchronization.
 */

/*
 * Acquire a resource.
 */
#define ACQUIRE(lkp, error, extflags, drain, wanted)			\
do {									\
	for (error = 0; wanted; ) {					\
		if ((drain))						\
			(lkp)->lk_flags |= LK_WAITDRAIN;		\
		else							\
			(lkp)->lk_waitcount++;				\
		/* XXX Cast away volatile. */				\
		error = tsleep((drain) ?				\
		    (void *)&(lkp)->lk_flags : (void *)(lkp),		\
		    (lkp)->lk_prio, (lkp)->lk_wmesg, (lkp)->lk_timo);	\
		if ((drain) == 0)					\
			(lkp)->lk_waitcount--;				\
		if (error)						\
			break;						\
	}								\
} while (0)

#define	SETHOLDER(lkp, pid, cpu_id)					\
	(lkp)->lk_lockholder = (pid)

#define	WEHOLDIT(lkp, pid, cpu_id)					\
	((lkp)->lk_lockholder == (pid))

/*
 * Initialize a lock; required before use.
 */
void
lockinit(struct lock *lkp, int prio, char *wmesg, int timo, int flags)
{

	bzero(lkp, sizeof(struct lock));
	lkp->lk_flags = flags & LK_EXTFLG_MASK;
	lkp->lk_lockholder = LK_NOPROC;
	lkp->lk_prio = prio;
	lkp->lk_timo = timo;
	lkp->lk_wmesg = wmesg;	/* just a name for spin locks */
}

/*
 * Determine the status of a lock.
 */
int
lockstatus(struct lock *lkp)
{
	int lock_type = 0;

	if (lkp->lk_exclusivecount != 0)
		lock_type = LK_EXCLUSIVE;
	else if (lkp->lk_sharecount != 0)
		lock_type = LK_SHARED;
	return (lock_type);
}

/*
 * Set, change, or release a lock.
 *
 * Shared requests increment the shared count. Exclusive requests set the
 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
 * accepted shared locks and shared-to-exclusive upgrades to go away.
 */
int
lockmgr(__volatile struct lock *lkp, u_int flags, void *notused)
{
	int error;
	pid_t pid;
	int extflags;
	cpuid_t cpu_id;
	struct proc *p = curproc;

	error = 0;
	extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;

#ifdef DIAGNOSTIC
	if (p == NULL)
		panic("lockmgr: process context required");
#endif		
	/* Process context required. */
	pid = p->p_pid;
	cpu_id = cpu_number();

	/*
	 * Once a lock has drained, the LK_DRAINING flag is set and an
	 * exclusive lock is returned. The only valid operation thereafter
	 * is a single release of that exclusive lock. This final release
	 * clears the LK_DRAINING flag and sets the LK_DRAINED flag. Any
	 * further requests of any sort will result in a panic. The bits
	 * selected for these two flags are chosen so that they will be set
	 * in memory that is freed (freed memory is filled with 0xdeadbeef).
	 */
	if (lkp->lk_flags & (LK_DRAINING|LK_DRAINED)) {
#ifdef DIAGNOSTIC
		if (lkp->lk_flags & LK_DRAINED)
			panic("lockmgr: using decommissioned lock");
		if ((flags & LK_TYPE_MASK) != LK_RELEASE ||
		    WEHOLDIT(lkp, pid, cpu_id) == 0)
			panic("lockmgr: non-release on draining lock: %d",
			    flags & LK_TYPE_MASK);
#endif /* DIAGNOSTIC */
		lkp->lk_flags &= ~LK_DRAINING;
		lkp->lk_flags |= LK_DRAINED;
	}

	/*
	 * Check if the caller is asking us to be schizophrenic.
	 */
	if ((lkp->lk_flags & (LK_CANRECURSE|LK_RECURSEFAIL)) ==
	    (LK_CANRECURSE|LK_RECURSEFAIL))
		panic("lockmgr: make up your mind");

	switch (flags & LK_TYPE_MASK) {

	case LK_SHARED:
		if (WEHOLDIT(lkp, pid, cpu_id) == 0) {
			/*
			 * If just polling, check to see if we will block.
			 */
			if ((extflags & LK_NOWAIT) && (lkp->lk_flags &
			    (LK_HAVE_EXCL | LK_WANT_EXCL))) {
				error = EBUSY;
				break;
			}
			/*
			 * Wait for exclusive locks and upgrades to clear.
			 */
			ACQUIRE(lkp, error, extflags, 0, lkp->lk_flags &
			    (LK_HAVE_EXCL | LK_WANT_EXCL));
			if (error)
				break;
			lkp->lk_sharecount++;
			break;
		}
		/*
		 * We hold an exclusive lock, so downgrade it to shared.
		 * An alternative would be to fail with EDEADLK.
		 */
		lkp->lk_sharecount++;

		if (WEHOLDIT(lkp, pid, cpu_id) == 0 ||
		    lkp->lk_exclusivecount == 0)
			panic("lockmgr: not holding exclusive lock");
		lkp->lk_sharecount += lkp->lk_exclusivecount;
		lkp->lk_exclusivecount = 0;
		lkp->lk_flags &= ~LK_HAVE_EXCL;
		SETHOLDER(lkp, LK_NOPROC, LK_NOCPU);
		if (lkp->lk_waitcount)
			wakeup((void *)(lkp));
		break;

	case LK_EXCLUSIVE:
		if (WEHOLDIT(lkp, pid, cpu_id)) {
			/*
			 * Recursive lock.
			 */
			if ((extflags & LK_CANRECURSE) == 0) {
				if (extflags & LK_RECURSEFAIL) {
					error = EDEADLK;
					break;
				} else
					panic("lockmgr: locking against myself");
			}
			lkp->lk_exclusivecount++;
			break;
		}
		/*
		 * If we are just polling, check to see if we will sleep.
		 */
		if ((extflags & LK_NOWAIT) && ((lkp->lk_flags &
		     (LK_HAVE_EXCL | LK_WANT_EXCL)) ||
		     lkp->lk_sharecount != 0)) {
			error = EBUSY;
			break;
		}
		/*
		 * Try to acquire the want_exclusive flag.
		 */
		ACQUIRE(lkp, error, extflags, 0, lkp->lk_flags &
		    (LK_HAVE_EXCL | LK_WANT_EXCL));
		if (error)
			break;
		lkp->lk_flags |= LK_WANT_EXCL;
		/*
		 * Wait for shared locks and upgrades to finish.
		 */
		ACQUIRE(lkp, error, extflags, 0, lkp->lk_sharecount != 0);
		lkp->lk_flags &= ~LK_WANT_EXCL;
		if (error)
			break;
		lkp->lk_flags |= LK_HAVE_EXCL;
		SETHOLDER(lkp, pid, cpu_id);
		if (lkp->lk_exclusivecount != 0)
			panic("lockmgr: non-zero exclusive count");
		lkp->lk_exclusivecount = 1;
		break;

	case LK_RELEASE:
		if (lkp->lk_exclusivecount != 0) {
			if (WEHOLDIT(lkp, pid, cpu_id) == 0) {
				panic("lockmgr: pid %d, not exclusive lock "
				    "holder %d unlocking",
				    pid, lkp->lk_lockholder);
			}
			lkp->lk_exclusivecount--;
			if (lkp->lk_exclusivecount == 0) {
				lkp->lk_flags &= ~LK_HAVE_EXCL;
				SETHOLDER(lkp, LK_NOPROC, LK_NOCPU);
			}
		} else if (lkp->lk_sharecount != 0) {
			lkp->lk_sharecount--;
		}
#ifdef DIAGNOSTIC
		else
			panic("lockmgr: release of unlocked lock!");
#endif
		if (lkp->lk_waitcount)
			wakeup((void *)(lkp));
		break;

	case LK_DRAIN:
		/*
		 * Check that we do not already hold the lock, as it can 
		 * never drain if we do. Unfortunately, we have no way to
		 * check for holding a shared lock, but at least we can
		 * check for an exclusive one.
		 */
		if (WEHOLDIT(lkp, pid, cpu_id))
			panic("lockmgr: draining against myself");
		/*
		 * If we are just polling, check to see if we will sleep.
		 */
		if ((extflags & LK_NOWAIT) && ((lkp->lk_flags &
		     (LK_HAVE_EXCL | LK_WANT_EXCL)) ||
		     lkp->lk_sharecount != 0 || lkp->lk_waitcount != 0)) {
			error = EBUSY;
			break;
		}
		ACQUIRE(lkp, error, extflags, 1,
		    ((lkp->lk_flags &
		     (LK_HAVE_EXCL | LK_WANT_EXCL)) ||
		     lkp->lk_sharecount != 0 ||
		     lkp->lk_waitcount != 0));
		if (error)
			break;
		lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
		SETHOLDER(lkp, pid, cpu_id);
		lkp->lk_exclusivecount = 1;
		break;

	default:
		panic("lockmgr: unknown locktype request %d",
		    flags & LK_TYPE_MASK);
		/* NOTREACHED */
	}
	if ((lkp->lk_flags & LK_WAITDRAIN) != 0 &&
	    ((lkp->lk_flags &
	    (LK_HAVE_EXCL | LK_WANT_EXCL)) == 0 &&
	    lkp->lk_sharecount == 0 && lkp->lk_waitcount == 0)) {
		lkp->lk_flags &= ~LK_WAITDRAIN;
		wakeup((void *)&lkp->lk_flags);
	}
	return (error);
}

#ifdef DIAGNOSTIC
/*
 * Print out information about state of a lock. Used by VOP_PRINT
 * routines to display status about contained locks.
 */
void
lockmgr_printinfo(__volatile struct lock *lkp)
{

	if (lkp->lk_sharecount)
		printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
		    lkp->lk_sharecount);
	else if (lkp->lk_flags & LK_HAVE_EXCL) {
		printf(" lock type %s: EXCL (count %d) by ",
		    lkp->lk_wmesg, lkp->lk_exclusivecount);
		printf("pid %d", lkp->lk_lockholder);
	} else
		printf(" not locked");
	if (lkp->lk_waitcount > 0)
		printf(" with %d pending", lkp->lk_waitcount);
}
#endif /* DIAGNOSTIC */

#if defined(MULTIPROCESSOR)
/*
 * Functions for manipulating the kernel_lock.  We put them here
 * so that they show up in profiles.
 */

struct __mp_lock kernel_lock; 

void
_kernel_lock_init(void)
{
	__mp_lock_init(&kernel_lock);
}

/*
 * Acquire/release the kernel lock.  Intended for use in the scheduler
 * and the lower half of the kernel.
 */

void
_kernel_lock(void)
{
	SCHED_ASSERT_UNLOCKED();
	__mp_lock(&kernel_lock);
}

void
_kernel_unlock(void)
{
	__mp_unlock(&kernel_lock);
}

/*
 * Acquire/release the kernel_lock on behalf of a process.  Intended for
 * use in the top half of the kernel.
 */
void
_kernel_proc_lock(struct proc *p)
{
	SCHED_ASSERT_UNLOCKED();
	__mp_lock(&kernel_lock);
	atomic_setbits_int(&p->p_flag, P_BIGLOCK);
}

void
_kernel_proc_unlock(struct proc *p)
{
	atomic_clearbits_int(&p->p_flag, P_BIGLOCK);
	__mp_unlock(&kernel_lock);
}

#ifdef MP_LOCKDEBUG
/* CPU-dependent timing, needs this to be settable from ddb. */
int __mp_lock_spinout = 200000000;
#endif

#endif /* MULTIPROCESSOR */