/* * Copyright (c) 1995 * The Regents of the University of California. All rights reserved. * * Copyright (C) 1997 * John S. Dyson. 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 * $FreeBSD$ */ #include <sys/param.h> #include <sys/proc.h> #include <sys/kernel.h> #include <sys/lock.h> #include <sys/malloc.h> #include <sys/mutex.h> #include <sys/systm.h> /* * Locking primitives implementation. * Locks provide shared/exclusive sychronization. */ #define LOCK_WAIT_TIME 100 #define LOCK_SAMPLE_WAIT 7 #if defined(DIAGNOSTIC) #define LOCK_INLINE #else #define LOCK_INLINE __inline #endif #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \ LK_SHARE_NONZERO | LK_WAIT_NONZERO) /* * Mutex array variables. Rather than each lockmgr lock having its own mutex, * share a fixed (at boot time) number of mutexes across all lockmgr locks in * order to keep sizeof(struct lock) down. */ extern int lock_nmtx; int lock_mtx_selector; struct mtx *lock_mtx_array; static struct mtx lock_mtx; static int acquire(struct lock *lkp, int extflags, int wanted); static int apause(struct lock *lkp, int flags); static int acquiredrain(struct lock *lkp, int extflags) ; static void lockmgr_init(void *dummy __unused) { int i; /* * Initialize the lockmgr protection mutex if it hasn't already been * done. Unless something changes about kernel startup order, VM * initialization will always cause this mutex to already be * initialized in a call to lockinit(). */ if (lock_mtx_selector == 0) mtx_init(&lock_mtx, "lockmgr", MTX_DEF); else { /* * This is necessary if (lock_nmtx == 1) and doesn't hurt * otherwise. */ lock_mtx_selector = 0; } lock_mtx_array = (struct mtx *)malloc(sizeof(struct mtx) * lock_nmtx, M_CACHE, M_WAITOK); for (i = 0; i < lock_nmtx; i++) mtx_init(&lock_mtx_array[i], "lockmgr interlock", MTX_DEF); } SYSINIT(lmgrinit, SI_SUB_LOCK, SI_ORDER_FIRST, lockmgr_init, NULL) static LOCK_INLINE void sharelock(struct lock *lkp, int incr) { lkp->lk_flags |= LK_SHARE_NONZERO; lkp->lk_sharecount += incr; } static LOCK_INLINE void shareunlock(struct lock *lkp, int decr) { KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr")); if (lkp->lk_sharecount == decr) { lkp->lk_flags &= ~LK_SHARE_NONZERO; if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) { wakeup(lkp); } lkp->lk_sharecount = 0; } else { lkp->lk_sharecount -= decr; } } /* * This is the waitloop optimization. */ static int apause(struct lock *lkp, int flags) { #ifdef SMP int i, lock_wait; #endif if ((lkp->lk_flags & flags) == 0) return 0; #ifdef SMP for (lock_wait = LOCK_WAIT_TIME; lock_wait > 0; lock_wait--) { mtx_unlock(lkp->lk_interlock); for (i = LOCK_SAMPLE_WAIT; i > 0; i--) if ((lkp->lk_flags & flags) == 0) break; mtx_lock(lkp->lk_interlock); if ((lkp->lk_flags & flags) == 0) return 0; } #endif return 1; } static int acquire(struct lock *lkp, int extflags, int wanted) { int s, error; CTR3(KTR_LOCKMGR, "acquire(): lkp == %p, extflags == 0x%x, wanted == 0x%x\n", lkp, extflags, wanted); if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) { return EBUSY; } if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) { error = apause(lkp, wanted); if (error == 0) return 0; } s = splhigh(); while ((lkp->lk_flags & wanted) != 0) { lkp->lk_flags |= LK_WAIT_NONZERO; lkp->lk_waitcount++; error = msleep(lkp, lkp->lk_interlock, lkp->lk_prio, lkp->lk_wmesg, lkp->lk_timo); if (lkp->lk_waitcount == 1) { lkp->lk_flags &= ~LK_WAIT_NONZERO; lkp->lk_waitcount = 0; } else { lkp->lk_waitcount--; } if (error) { splx(s); return error; } if (extflags & LK_SLEEPFAIL) { splx(s); return ENOLCK; } } splx(s); return 0; } /* * 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 #ifndef DEBUG_LOCKS lockmgr(lkp, flags, interlkp, p) #else debuglockmgr(lkp, flags, interlkp, p, name, file, line) #endif struct lock *lkp; u_int flags; struct mtx *interlkp; struct proc *p; #ifdef DEBUG_LOCKS const char *name; /* Name of lock function */ const char *file; /* Name of file call is from */ int line; /* Line number in file */ #endif { int error; pid_t pid; int extflags, lockflags; CTR5(KTR_LOCKMGR, "lockmgr(): lkp == %p (lk_wmesg == \"%s\"), flags == 0x%x, " "interlkp == %p, p == %p", lkp, lkp->lk_wmesg, flags, interlkp, p); error = 0; if (p == NULL) pid = LK_KERNPROC; else pid = p->p_pid; mtx_lock(lkp->lk_interlock); if (flags & LK_INTERLOCK) { mtx_assert(interlkp, MA_OWNED | MA_NOTRECURSED); mtx_unlock(interlkp); } extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; switch (flags & LK_TYPE_MASK) { case LK_SHARED: /* * If we are not the exclusive lock holder, we have to block * while there is an exclusive lock holder or while an * exclusive lock request or upgrade request is in progress. * * However, if P_DEADLKTREAT is set, we override exclusive * lock requests or upgrade requests ( but not the exclusive * lock itself ). */ if (lkp->lk_lockholder != pid) { lockflags = LK_HAVE_EXCL; if (p) { PROC_LOCK(p); if (!(p->p_flag & P_DEADLKTREAT)) { lockflags |= LK_WANT_EXCL | LK_WANT_UPGRADE; } PROC_UNLOCK(p); } error = acquire(lkp, extflags, lockflags); if (error) break; sharelock(lkp, 1); break; } /* * We hold an exclusive lock, so downgrade it to shared. * An alternative would be to fail with EDEADLK. */ sharelock(lkp, 1); /* fall into downgrade */ case LK_DOWNGRADE: KASSERT(lkp->lk_lockholder == pid && lkp->lk_exclusivecount != 0, ("lockmgr: not holding exclusive lock " "(owner pid (%d) != pid (%d), exlcnt (%d) != 0", lkp->lk_lockholder, pid, lkp->lk_exclusivecount)); sharelock(lkp, 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) { shareunlock(lkp, 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"); shareunlock(lkp, 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; error = acquire(lkp, extflags, LK_SHARE_NONZERO); 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; #if defined(DEBUG_LOCKS) lkp->lk_filename = file; lkp->lk_lineno = line; lkp->lk_lockername = name; #endif 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_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == LK_WAIT_NONZERO) wakeup((void *)lkp); /* fall into exclusive request */ case LK_EXCLUSIVE: if (lkp->lk_lockholder == pid && pid != LK_KERNPROC) { /* * Recursive lock. */ if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) panic("lockmgr: locking against myself"); if ((extflags & LK_CANRECURSE) != 0) { 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 | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { error = EBUSY; break; } /* * Try to acquire the want_exclusive flag. */ error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); if (error) break; lkp->lk_flags |= LK_WANT_EXCL; /* * Wait for shared locks and upgrades to finish. */ error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO); 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; #if defined(DEBUG_LOCKS) lkp->lk_filename = file; lkp->lk_lineno = line; lkp->lk_lockername = name; #endif break; case LK_RELEASE: if (lkp->lk_exclusivecount != 0) { if (lkp->lk_lockholder != pid && lkp->lk_lockholder != LK_KERNPROC) { panic("lockmgr: pid %d, not %s %d unlocking", pid, "exclusive lock holder", lkp->lk_lockholder); } if (lkp->lk_exclusivecount == 1) { lkp->lk_flags &= ~LK_HAVE_EXCL; lkp->lk_lockholder = LK_NOPROC; lkp->lk_exclusivecount = 0; } else { lkp->lk_exclusivecount--; } } else if (lkp->lk_flags & LK_SHARE_NONZERO) shareunlock(lkp, 1); if (lkp->lk_flags & LK_WAIT_NONZERO) 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"); error = acquiredrain(lkp, extflags); if (error) break; lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; lkp->lk_lockholder = pid; lkp->lk_exclusivecount = 1; #if defined(DEBUG_LOCKS) lkp->lk_filename = file; lkp->lk_lineno = line; lkp->lk_lockername = name; #endif break; default: mtx_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 | LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) { lkp->lk_flags &= ~LK_WAITDRAIN; wakeup((void *)&lkp->lk_flags); } mtx_unlock(lkp->lk_interlock); return (error); } static int acquiredrain(struct lock *lkp, int extflags) { int error; if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) { return EBUSY; } error = apause(lkp, LK_ALL); if (error == 0) return 0; while (lkp->lk_flags & LK_ALL) { lkp->lk_flags |= LK_WAITDRAIN; error = msleep(&lkp->lk_flags, lkp->lk_interlock, lkp->lk_prio, lkp->lk_wmesg, lkp->lk_timo); if (error) return error; if (extflags & LK_SLEEPFAIL) { return ENOLCK; } } return 0; } /* * Initialize a lock; required before use. */ void lockinit(lkp, prio, wmesg, timo, flags) struct lock *lkp; int prio; char *wmesg; int timo; int flags; { CTR5(KTR_LOCKMGR, "lockinit(): lkp == %p, prio == %d, wmesg == \"%s\", " "timo == %d, flags = 0x%x\n", lkp, prio, wmesg, timo, flags); if (lock_mtx_array != NULL) { mtx_lock(&lock_mtx); lkp->lk_interlock = &lock_mtx_array[lock_mtx_selector]; lock_mtx_selector++; if (lock_mtx_selector == lock_nmtx) lock_mtx_selector = 0; mtx_unlock(&lock_mtx); } else { /* * Giving lockmgr locks that are initialized during boot a * pointer to the internal lockmgr mutex is safe, since the * lockmgr code itself doesn't call lockinit() (which could * cause mutex recursion). */ if (lock_mtx_selector == 0) { /* * This case only happens during kernel bootstrapping, * so there's no reason to protect modification of * lock_mtx_selector or lock_mtx. */ mtx_init(&lock_mtx, "lockmgr", MTX_DEF); lock_mtx_selector = 1; } lkp->lk_interlock = &lock_mtx; } lkp->lk_flags = (flags & LK_EXTFLG_MASK); lkp->lk_sharecount = 0; lkp->lk_waitcount = 0; lkp->lk_exclusivecount = 0; lkp->lk_prio = prio; lkp->lk_wmesg = wmesg; lkp->lk_timo = timo; lkp->lk_lockholder = LK_NOPROC; } /* * Destroy a lock. */ void lockdestroy(lkp) struct lock *lkp; { CTR2(KTR_LOCKMGR, "lockdestroy(): lkp == %p (lk_wmesg == \"%s\")", lkp, lkp->lk_wmesg); } /* * Determine the status of a lock. */ int lockstatus(lkp, p) struct lock *lkp; struct proc *p; { int lock_type = 0; mtx_lock(lkp->lk_interlock); if (lkp->lk_exclusivecount != 0) { if (p == NULL || lkp->lk_lockholder == p->p_pid) lock_type = LK_EXCLUSIVE; else lock_type = LK_EXCLOTHER; } else if (lkp->lk_sharecount != 0) lock_type = LK_SHARED; mtx_unlock(lkp->lk_interlock); return (lock_type); } /* * Determine the number of holders of a lock. */ int lockcount(lkp) struct lock *lkp; { int count; mtx_lock(lkp->lk_interlock); count = lkp->lk_exclusivecount + lkp->lk_sharecount; mtx_unlock(lkp->lk_interlock); return (count); } /* * Print out information about state of a lock. Used by VOP_PRINT * routines to display status 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); }