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7181624aaa
is useful as a last effort in debugging file system deadlocks. This is enabled via 'options DEBUG_LOCKS'
595 lines
15 KiB
C
595 lines
15 KiB
C
/*
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* Copyright (c) 1995
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* The Regents of the University of California. All rights reserved.
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*
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* Copyright (C) 1997
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* John S. Dyson. All rights reserved.
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*
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* This code contains ideas from software contributed to Berkeley by
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* Avadis Tevanian, Jr., Michael Wayne Young, and the Mach Operating
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* System project at Carnegie-Mellon University.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)kern_lock.c 8.18 (Berkeley) 5/21/95
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* $FreeBSD$
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*/
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#include <sys/param.h>
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#include <sys/proc.h>
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#include <sys/kernel.h>
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#include <sys/ktr.h>
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#include <sys/lock.h>
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#include <sys/malloc.h>
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#include <sys/mutex.h>
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#include <sys/systm.h>
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/*
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* Locking primitives implementation.
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* Locks provide shared/exclusive sychronization.
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*/
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#define LOCK_WAIT_TIME 100
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#define LOCK_SAMPLE_WAIT 7
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#if defined(DIAGNOSTIC)
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#define LOCK_INLINE
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#else
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#define LOCK_INLINE __inline
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#endif
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#define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
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LK_SHARE_NONZERO | LK_WAIT_NONZERO)
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/*
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* Mutex array variables. Rather than each lockmgr lock having its own mutex,
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* share a fixed (at boot time) number of mutexes across all lockmgr locks in
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* order to keep sizeof(struct lock) down.
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*/
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int lock_mtx_valid;
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static struct mtx lock_mtx;
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static int acquire(struct lock *lkp, int extflags, int wanted);
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static int apause(struct lock *lkp, int flags);
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static int acquiredrain(struct lock *lkp, int extflags) ;
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static void
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lockmgr_init(void *dummy __unused)
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{
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/*
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* Initialize the lockmgr protection mutex if it hasn't already been
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* done. Unless something changes about kernel startup order, VM
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* initialization will always cause this mutex to already be
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* initialized in a call to lockinit().
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*/
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if (lock_mtx_valid == 0) {
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mtx_init(&lock_mtx, "lockmgr", NULL, MTX_DEF);
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lock_mtx_valid = 1;
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}
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}
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SYSINIT(lmgrinit, SI_SUB_LOCK, SI_ORDER_FIRST, lockmgr_init, NULL)
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static LOCK_INLINE void
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sharelock(struct lock *lkp, int incr) {
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lkp->lk_flags |= LK_SHARE_NONZERO;
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lkp->lk_sharecount += incr;
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}
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static LOCK_INLINE void
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shareunlock(struct lock *lkp, int decr) {
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KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
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if (lkp->lk_sharecount == decr) {
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lkp->lk_flags &= ~LK_SHARE_NONZERO;
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if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
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wakeup(lkp);
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}
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lkp->lk_sharecount = 0;
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} else {
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lkp->lk_sharecount -= decr;
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}
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}
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/*
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* This is the waitloop optimization.
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*/
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static int
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apause(struct lock *lkp, int flags)
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{
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#ifdef SMP
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int i, lock_wait;
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#endif
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if ((lkp->lk_flags & flags) == 0)
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return 0;
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#ifdef SMP
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for (lock_wait = LOCK_WAIT_TIME; lock_wait > 0; lock_wait--) {
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mtx_unlock(lkp->lk_interlock);
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for (i = LOCK_SAMPLE_WAIT; i > 0; i--)
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if ((lkp->lk_flags & flags) == 0)
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break;
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mtx_lock(lkp->lk_interlock);
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if ((lkp->lk_flags & flags) == 0)
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return 0;
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}
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#endif
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return 1;
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}
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static int
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acquire(struct lock *lkp, int extflags, int wanted) {
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int s, error;
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CTR3(KTR_LOCKMGR,
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"acquire(): lkp == %p, extflags == 0x%x, wanted == 0x%x\n",
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lkp, extflags, wanted);
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if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) {
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return EBUSY;
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}
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if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) {
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error = apause(lkp, wanted);
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if (error == 0)
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return 0;
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}
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s = splhigh();
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while ((lkp->lk_flags & wanted) != 0) {
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lkp->lk_flags |= LK_WAIT_NONZERO;
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lkp->lk_waitcount++;
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error = msleep(lkp, lkp->lk_interlock, lkp->lk_prio,
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lkp->lk_wmesg,
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((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
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if (lkp->lk_waitcount == 1) {
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lkp->lk_flags &= ~LK_WAIT_NONZERO;
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lkp->lk_waitcount = 0;
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} else {
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lkp->lk_waitcount--;
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}
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if (error) {
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splx(s);
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return error;
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}
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if (extflags & LK_SLEEPFAIL) {
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splx(s);
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return ENOLCK;
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}
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}
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splx(s);
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return 0;
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}
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/*
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* Set, change, or release a lock.
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*
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* Shared requests increment the shared count. Exclusive requests set the
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* LK_WANT_EXCL flag (preventing further shared locks), and wait for already
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* accepted shared locks and shared-to-exclusive upgrades to go away.
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*/
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int
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#ifndef DEBUG_LOCKS
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lockmgr(lkp, flags, interlkp, td)
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#else
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debuglockmgr(lkp, flags, interlkp, td, name, file, line)
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#endif
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struct lock *lkp;
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u_int flags;
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struct mtx *interlkp;
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struct thread *td;
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#ifdef DEBUG_LOCKS
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const char *name; /* Name of lock function */
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const char *file; /* Name of file call is from */
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int line; /* Line number in file */
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#endif
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{
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int error;
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pid_t pid;
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int extflags, lockflags;
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CTR5(KTR_LOCKMGR,
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"lockmgr(): lkp == %p (lk_wmesg == \"%s\"), flags == 0x%x, "
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"interlkp == %p, td == %p", lkp, lkp->lk_wmesg, flags, interlkp, td);
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error = 0;
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if (td == NULL)
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pid = LK_KERNPROC;
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else
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pid = td->td_proc->p_pid;
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mtx_lock(lkp->lk_interlock);
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if (flags & LK_INTERLOCK) {
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mtx_assert(interlkp, MA_OWNED | MA_NOTRECURSED);
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mtx_unlock(interlkp);
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}
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if (panicstr != NULL) {
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mtx_unlock(lkp->lk_interlock);
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return (0);
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}
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extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
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switch (flags & LK_TYPE_MASK) {
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case LK_SHARED:
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/*
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* If we are not the exclusive lock holder, we have to block
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* while there is an exclusive lock holder or while an
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* exclusive lock request or upgrade request is in progress.
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*
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* However, if TDF_DEADLKTREAT is set, we override exclusive
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* lock requests or upgrade requests ( but not the exclusive
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* lock itself ).
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*/
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if (lkp->lk_lockholder != pid) {
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lockflags = LK_HAVE_EXCL;
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mtx_lock_spin(&sched_lock);
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if (td != NULL && !(td->td_flags & TDF_DEADLKTREAT))
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lockflags |= LK_WANT_EXCL | LK_WANT_UPGRADE;
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mtx_unlock_spin(&sched_lock);
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error = acquire(lkp, extflags, lockflags);
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if (error)
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break;
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sharelock(lkp, 1);
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#if defined(DEBUG_LOCKS)
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lkp->lk_slockholder = pid;
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lkp->lk_sfilename = file;
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lkp->lk_slineno = line;
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lkp->lk_slockername = name;
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#endif
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break;
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}
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/*
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* We hold an exclusive lock, so downgrade it to shared.
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* An alternative would be to fail with EDEADLK.
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*/
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sharelock(lkp, 1);
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/* fall into downgrade */
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case LK_DOWNGRADE:
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KASSERT(lkp->lk_lockholder == pid && lkp->lk_exclusivecount != 0,
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("lockmgr: not holding exclusive lock "
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"(owner pid (%d) != pid (%d), exlcnt (%d) != 0",
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lkp->lk_lockholder, pid, lkp->lk_exclusivecount));
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sharelock(lkp, lkp->lk_exclusivecount);
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lkp->lk_exclusivecount = 0;
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lkp->lk_flags &= ~LK_HAVE_EXCL;
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lkp->lk_lockholder = LK_NOPROC;
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if (lkp->lk_waitcount)
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wakeup((void *)lkp);
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break;
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case LK_EXCLUPGRADE:
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/*
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* If another process is ahead of us to get an upgrade,
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* then we want to fail rather than have an intervening
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* exclusive access.
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*/
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if (lkp->lk_flags & LK_WANT_UPGRADE) {
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shareunlock(lkp, 1);
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error = EBUSY;
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break;
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}
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/* fall into normal upgrade */
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case LK_UPGRADE:
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/*
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* Upgrade a shared lock to an exclusive one. If another
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* shared lock has already requested an upgrade to an
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* exclusive lock, our shared lock is released and an
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* exclusive lock is requested (which will be granted
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* after the upgrade). If we return an error, the file
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* will always be unlocked.
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*/
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if ((lkp->lk_lockholder == pid) || (lkp->lk_sharecount <= 0))
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panic("lockmgr: upgrade exclusive lock");
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shareunlock(lkp, 1);
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/*
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* If we are just polling, check to see if we will block.
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*/
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if ((extflags & LK_NOWAIT) &&
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((lkp->lk_flags & LK_WANT_UPGRADE) ||
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lkp->lk_sharecount > 1)) {
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error = EBUSY;
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break;
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}
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if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
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/*
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* We are first shared lock to request an upgrade, so
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* request upgrade and wait for the shared count to
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* drop to zero, then take exclusive lock.
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*/
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lkp->lk_flags |= LK_WANT_UPGRADE;
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error = acquire(lkp, extflags, LK_SHARE_NONZERO);
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lkp->lk_flags &= ~LK_WANT_UPGRADE;
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if (error)
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break;
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lkp->lk_flags |= LK_HAVE_EXCL;
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lkp->lk_lockholder = pid;
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if (lkp->lk_exclusivecount != 0)
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panic("lockmgr: non-zero exclusive count");
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lkp->lk_exclusivecount = 1;
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#if defined(DEBUG_LOCKS)
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lkp->lk_filename = file;
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lkp->lk_lineno = line;
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lkp->lk_lockername = name;
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#endif
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break;
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}
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/*
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* Someone else has requested upgrade. Release our shared
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* lock, awaken upgrade requestor if we are the last shared
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* lock, then request an exclusive lock.
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*/
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if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
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LK_WAIT_NONZERO)
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wakeup((void *)lkp);
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/* fall into exclusive request */
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case LK_EXCLUSIVE:
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if (lkp->lk_lockholder == pid && pid != LK_KERNPROC) {
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/*
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* Recursive lock.
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*/
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if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0)
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panic("lockmgr: locking against myself");
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if ((extflags & LK_CANRECURSE) != 0) {
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lkp->lk_exclusivecount++;
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break;
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}
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}
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/*
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* If we are just polling, check to see if we will sleep.
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*/
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if ((extflags & LK_NOWAIT) &&
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(lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
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error = EBUSY;
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break;
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}
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/*
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* Try to acquire the want_exclusive flag.
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*/
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error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL));
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if (error)
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break;
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lkp->lk_flags |= LK_WANT_EXCL;
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/*
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* Wait for shared locks and upgrades to finish.
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*/
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error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO);
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lkp->lk_flags &= ~LK_WANT_EXCL;
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if (error)
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break;
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lkp->lk_flags |= LK_HAVE_EXCL;
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lkp->lk_lockholder = pid;
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if (lkp->lk_exclusivecount != 0)
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panic("lockmgr: non-zero exclusive count");
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lkp->lk_exclusivecount = 1;
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#if defined(DEBUG_LOCKS)
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lkp->lk_filename = file;
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lkp->lk_lineno = line;
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lkp->lk_lockername = name;
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#endif
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break;
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case LK_RELEASE:
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if (lkp->lk_exclusivecount != 0) {
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if (lkp->lk_lockholder != pid &&
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lkp->lk_lockholder != LK_KERNPROC) {
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panic("lockmgr: pid %d, not %s %d unlocking",
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pid, "exclusive lock holder",
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lkp->lk_lockholder);
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}
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if (lkp->lk_exclusivecount == 1) {
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lkp->lk_flags &= ~LK_HAVE_EXCL;
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lkp->lk_lockholder = LK_NOPROC;
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lkp->lk_exclusivecount = 0;
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} else {
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lkp->lk_exclusivecount--;
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}
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} else if (lkp->lk_flags & LK_SHARE_NONZERO)
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shareunlock(lkp, 1);
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if (lkp->lk_flags & LK_WAIT_NONZERO)
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wakeup((void *)lkp);
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break;
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case LK_DRAIN:
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/*
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* Check that we do not already hold the lock, as it can
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* never drain if we do. Unfortunately, we have no way to
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* check for holding a shared lock, but at least we can
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* check for an exclusive one.
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*/
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if (lkp->lk_lockholder == pid)
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panic("lockmgr: draining against myself");
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error = acquiredrain(lkp, extflags);
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if (error)
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break;
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lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
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lkp->lk_lockholder = pid;
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lkp->lk_exclusivecount = 1;
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#if defined(DEBUG_LOCKS)
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lkp->lk_filename = file;
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lkp->lk_lineno = line;
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lkp->lk_lockername = name;
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#endif
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break;
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default:
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mtx_unlock(lkp->lk_interlock);
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panic("lockmgr: unknown locktype request %d",
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flags & LK_TYPE_MASK);
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/* NOTREACHED */
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}
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if ((lkp->lk_flags & LK_WAITDRAIN) &&
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(lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE |
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LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) {
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lkp->lk_flags &= ~LK_WAITDRAIN;
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wakeup((void *)&lkp->lk_flags);
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}
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mtx_unlock(lkp->lk_interlock);
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return (error);
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}
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static int
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acquiredrain(struct lock *lkp, int extflags) {
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int error;
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if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) {
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return EBUSY;
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}
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error = apause(lkp, LK_ALL);
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if (error == 0)
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return 0;
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while (lkp->lk_flags & LK_ALL) {
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lkp->lk_flags |= LK_WAITDRAIN;
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error = msleep(&lkp->lk_flags, lkp->lk_interlock, lkp->lk_prio,
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lkp->lk_wmesg,
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((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
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if (error)
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return error;
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if (extflags & LK_SLEEPFAIL) {
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return ENOLCK;
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}
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}
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return 0;
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}
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/*
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* Initialize a lock; required before use.
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*/
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void
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lockinit(lkp, prio, wmesg, timo, flags)
|
|
struct lock *lkp;
|
|
int prio;
|
|
const 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_valid == 0) {
|
|
mtx_init(&lock_mtx, "lockmgr", NULL, MTX_DEF);
|
|
lock_mtx_valid = 1;
|
|
}
|
|
/*
|
|
* XXX cleanup - make sure mtxpool is always initialized before
|
|
* this is ever called.
|
|
*/
|
|
if (mtx_pool_valid) {
|
|
mtx_lock(&lock_mtx);
|
|
lkp->lk_interlock = mtx_pool_alloc();
|
|
mtx_unlock(&lock_mtx);
|
|
} else {
|
|
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, td)
|
|
struct lock *lkp;
|
|
struct thread *td;
|
|
{
|
|
int lock_type = 0;
|
|
|
|
mtx_lock(lkp->lk_interlock);
|
|
if (lkp->lk_exclusivecount != 0) {
|
|
if (td == NULL || lkp->lk_lockholder == td->td_proc->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);
|
|
}
|