/* $OpenBSD: kern_lock.c,v 1.9 1999/07/09 15:17:59 art 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. All advertising materials mentioning features or use of this software * must display the following acknowledgement: * This product includes software developed by the University of * California, Berkeley and its contributors. * 4. 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 <machine/cpu.h> void record_stacktrace __P((int *, int)); void playback_stacktrace __P((int *, int)); /* * Locking primitives implementation. * Locks provide shared/exclusive sychronization. */ #if 0 #ifdef DEBUG #define COUNT(p, x) if (p) (p)->p_locks += (x) #else #define COUNT(p, x) #endif #endif #define COUNT(p, x) #if NCPUS > 1 /* * For multiprocessor system, try spin lock first. * * This should be inline expanded below, but we cannot have #if * inside a multiline define. */ int lock_wait_time = 100; #define PAUSE(lkp, wanted) \ if (lock_wait_time > 0) { \ int i; \ \ simple_unlock(&lkp->lk_interlock); \ for (i = lock_wait_time; i > 0; i--) \ if (!(wanted)) \ break; \ simple_lock(&lkp->lk_interlock); \ } \ if (!(wanted)) \ break; #else /* NCPUS == 1 */ /* * It is an error to spin on a uniprocessor as nothing will ever cause * the simple lock to clear while we are executing. */ #define PAUSE(lkp, wanted) #endif /* NCPUS == 1 */ /* * Acquire a resource. */ #define ACQUIRE(lkp, error, extflags, wanted) \ PAUSE(lkp, wanted); \ for (error = 0; wanted; ) { \ (lkp)->lk_waitcount++; \ simple_unlock(&(lkp)->lk_interlock); \ error = tsleep((void *)lkp, (lkp)->lk_prio, \ (lkp)->lk_wmesg, (lkp)->lk_timo); \ simple_lock(&(lkp)->lk_interlock); \ (lkp)->lk_waitcount--; \ if (error) \ break; \ if ((extflags) & LK_SLEEPFAIL) { \ error = ENOLCK; \ break; \ } \ } /* * Initialize a lock; required before use. */ void lockinit(lkp, prio, wmesg, timo, flags) struct lock *lkp; int prio; char *wmesg; int timo; int flags; { bzero(lkp, sizeof(struct lock)); simple_lock_init(&lkp->lk_interlock); lkp->lk_flags = flags & LK_EXTFLG_MASK; lkp->lk_prio = prio; lkp->lk_timo = timo; lkp->lk_wmesg = wmesg; lkp->lk_lockholder = LK_NOPROC; } /* * Determine the status of a lock. */ int lockstatus(lkp) struct lock *lkp; { int lock_type = 0; simple_lock(&lkp->lk_interlock); if (lkp->lk_exclusivecount != 0) lock_type = LK_EXCLUSIVE; else if (lkp->lk_sharecount != 0) lock_type = LK_SHARED; simple_unlock(&lkp->lk_interlock); 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(lkp, flags, interlkp, p) __volatile struct lock *lkp; u_int flags; struct simplelock *interlkp; struct proc *p; { int error; pid_t pid; int extflags; error = 0; if (p) pid = p->p_pid; else pid = LK_KERNPROC; simple_lock(&lkp->lk_interlock); if (flags & LK_INTERLOCK) simple_unlock(interlkp); extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; #ifdef DIAGNOSTIC /* * 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). * The final release is permitted to give a new lease on life to * the lock by specifying LK_REENABLE. */ if (lkp->lk_flags & (LK_DRAINING|LK_DRAINED)) { if (lkp->lk_flags & LK_DRAINED) panic("lockmgr: using decommissioned lock"); if ((flags & LK_TYPE_MASK) != LK_RELEASE || lkp->lk_lockholder != pid) panic("lockmgr: non-release on draining lock: %d", flags & LK_TYPE_MASK); lkp->lk_flags &= ~LK_DRAINING; if ((flags & LK_REENABLE) == 0) lkp->lk_flags |= LK_DRAINED; } #endif /* DIAGNOSTIC */ switch (flags & LK_TYPE_MASK) { case LK_SHARED: if (lkp->lk_lockholder != pid) { /* * If just polling, check to see if we will block. */ if ((extflags & LK_NOWAIT) && (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE))) { error = EBUSY; break; } /* * Wait for exclusive locks and upgrades to clear. */ ACQUIRE(lkp, error, extflags, lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)); if (error) break; lkp->lk_sharecount++; COUNT(p, 1); break; } /* * We hold an exclusive lock, so downgrade it to shared. * An alternative would be to fail with EDEADLK. */ lkp->lk_sharecount++; COUNT(p, 1); /* fall into downgrade */ case LK_DOWNGRADE: if (lkp->lk_lockholder != pid || 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; lkp->lk_lockholder = LK_NOPROC; if (lkp->lk_waitcount) wakeup((void *)lkp); break; case LK_EXCLUPGRADE: /* * If another process is ahead of us to get an upgrade, * then we want to fail rather than have an intervening * exclusive access. */ if (lkp->lk_flags & LK_WANT_UPGRADE) { lkp->lk_sharecount--; COUNT(p, -1); error = EBUSY; break; } /* fall into normal upgrade */ case LK_UPGRADE: /* * Upgrade a shared lock to an exclusive one. If another * shared lock has already requested an upgrade to an * exclusive lock, our shared lock is released and an * exclusive lock is requested (which will be granted * after the upgrade). If we return an error, the file * will always be unlocked. */ if (lkp->lk_lockholder == pid || lkp->lk_sharecount <= 0) panic("lockmgr: upgrade exclusive lock"); lkp->lk_sharecount--; COUNT(p, -1); /* * If we are just polling, check to see if we will block. */ if ((extflags & LK_NOWAIT) && ((lkp->lk_flags & LK_WANT_UPGRADE) || lkp->lk_sharecount > 1)) { error = EBUSY; break; } if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { /* * We are first shared lock to request an upgrade, so * request upgrade and wait for the shared count to * drop to zero, then take exclusive lock. */ lkp->lk_flags |= LK_WANT_UPGRADE; ACQUIRE(lkp, error, extflags, lkp->lk_sharecount); lkp->lk_flags &= ~LK_WANT_UPGRADE; if (error) break; lkp->lk_flags |= LK_HAVE_EXCL; lkp->lk_lockholder = pid; if (lkp->lk_exclusivecount != 0) panic("lockmgr: non-zero exclusive count"); lkp->lk_exclusivecount = 1; COUNT(p, 1); break; } /* * Someone else has requested upgrade. Release our shared * lock, awaken upgrade requestor if we are the last shared * lock, then request an exclusive lock. */ if (lkp->lk_sharecount == 0 && lkp->lk_waitcount) wakeup((void *)lkp); /* fall into exclusive request */ case LK_EXCLUSIVE: if (lkp->lk_lockholder == pid && pid != LK_KERNPROC) { /* * Recursive lock. */ if ((extflags & LK_CANRECURSE) == 0) panic("lockmgr: locking against myself"); lkp->lk_exclusivecount++; COUNT(p, 1); 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 | LK_WANT_UPGRADE)) || lkp->lk_sharecount != 0)) { error = EBUSY; break; } /* * Try to acquire the want_exclusive flag. */ ACQUIRE(lkp, error, extflags, 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, lkp->lk_sharecount != 0 || (lkp->lk_flags & LK_WANT_UPGRADE)); lkp->lk_flags &= ~LK_WANT_EXCL; if (error) break; lkp->lk_flags |= LK_HAVE_EXCL; lkp->lk_lockholder = pid; if (lkp->lk_exclusivecount != 0) panic("lockmgr: non-zero exclusive count"); lkp->lk_exclusivecount = 1; COUNT(p, 1); break; case LK_RELEASE: if (lkp->lk_exclusivecount != 0) { if (pid != lkp->lk_lockholder) panic("lockmgr: pid %d, not %s %d unlocking", pid, "exclusive lock holder", lkp->lk_lockholder); lkp->lk_exclusivecount--; COUNT(p, -1); if (lkp->lk_exclusivecount == 0) { lkp->lk_flags &= ~LK_HAVE_EXCL; lkp->lk_lockholder = LK_NOPROC; } } else if (lkp->lk_sharecount != 0) { lkp->lk_sharecount--; COUNT(p, -1); } 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 (lkp->lk_lockholder == pid) 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 | LK_WANT_UPGRADE)) || lkp->lk_sharecount != 0 || lkp->lk_waitcount != 0)) { error = EBUSY; break; } PAUSE(lkp, ((lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)) || lkp->lk_sharecount != 0 || lkp->lk_waitcount != 0)); for (error = 0; ((lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)) || lkp->lk_sharecount != 0 || lkp->lk_waitcount != 0); ) { lkp->lk_flags |= LK_WAITDRAIN; simple_unlock(&lkp->lk_interlock); if ((error = tsleep((void *)&lkp->lk_flags, lkp->lk_prio, lkp->lk_wmesg, lkp->lk_timo)) != 0) return (error); if ((extflags) & LK_SLEEPFAIL) return (ENOLCK); simple_lock(&lkp->lk_interlock); } lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; lkp->lk_lockholder = pid; lkp->lk_exclusivecount = 1; COUNT(p, 1); break; default: simple_unlock(&lkp->lk_interlock); panic("lockmgr: unknown locktype request %d", flags & LK_TYPE_MASK); /* NOTREACHED */ } if ((lkp->lk_flags & LK_WAITDRAIN) && ((lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)) == 0 && lkp->lk_sharecount == 0 && lkp->lk_waitcount == 0)) { lkp->lk_flags &= ~LK_WAITDRAIN; wakeup((void *)&lkp->lk_flags); } simple_unlock(&lkp->lk_interlock); return (error); } /* * Print out information about state of a lock. Used by VOP_PRINT * routines to display ststus about contained locks. */ void lockmgr_printinfo(lkp) 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 pid %d", lkp->lk_wmesg, lkp->lk_exclusivecount, lkp->lk_lockholder); if (lkp->lk_waitcount > 0) printf(" with %d pending", lkp->lk_waitcount); } #if defined(LOCKDEBUG) int lockdebug_print = 0; int lockdebug_debugger = 0; /* * Simple lock functions so that the debugger can see from whence * they are being called. */ void simple_lock_init(lkp) struct simplelock *lkp; { lkp->lock_data = SLOCK_UNLOCKED; } void _simple_lock(lkp, id, l) __volatile struct simplelock *lkp; const char *id; int l; { if (lkp->lock_data == SLOCK_LOCKED) { if (lockdebug_print) printf("%s:%d simple_lock: lock held...\n", id, l); if (lockdebug_debugger) Debugger(); } lkp->lock_data = SLOCK_LOCKED; } int _simple_lock_try(lkp, id, l) __volatile struct simplelock *lkp; const char *id; int l; { if (lkp->lock_data == SLOCK_LOCKED) { if (lockdebug_print) printf("%s:%d simple_lock: lock held...\n", id, l); if (lockdebug_debugger) Debugger(); } return lkp->lock_data = SLOCK_LOCKED; } void _simple_unlock(lkp, id, l) __volatile struct simplelock *lkp; const char *id; int l; { if (lkp->lock_data == SLOCK_UNLOCKED) { if (lockdebug_print) printf("%s:%d simple_unlock: lock not held...\n", id, l); if (lockdebug_debugger) Debugger(); } lkp->lock_data = SLOCK_UNLOCKED; } void _simple_lock_assert(lkp, state, id, l) __volatile struct simplelock *lkp; const char *id; int l; { if (lkp->lock_data != state) { if (lockdebug_print) printf("%s:%d simple_lock_assert: wrong state: %d", id, l, lkp->lock_data); if (lockdebug_debugger) Debugger(); } } #endif /* LOCKDEBUG */