/*
* Copyright (c) 1982, 1986, 1989, 1993
* The Regents of the University of California. All rights reserved.
*
* This code is derived from software contributed to Berkeley by
* Scooter Morris at Genentech Inc.
*
* 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.
*
* @(#)ufs_lockf.c 8.4 (Berkeley) 10/26/94
*/
/*
* The lockf structure is a kernel structure which contains the information
* associated with a byte range lock. The lockf structures are linked into
* the vnode structure. Locks are sorted by the starting byte of the lock for
* efficiency.
*
* lf_next is used for two purposes, depending on whether the lock is
* being held, or is in conflict with an existing lock. If this lock
* is held, it indicates the next lock on the same vnode.
* For pending locks, if lock->lf_next is non-NULL, then lock->lf_block
* must be queued on the lf_blkhd TAILQ of lock->lf_next.
*/
TAILQ_HEAD(locklist, lockf);
struct lockf {
kcondvar_t lf_cv; /* Signalling */
short lf_flags; /* Lock semantics: F_POSIX, F_FLOCK, F_WAIT */
short lf_type; /* Lock type: F_RDLCK, F_WRLCK */
off_t lf_start; /* The byte # of the start of the lock */
off_t lf_end; /* The byte # of the end of the lock (-1=EOF)*/
void *lf_id; /* process or file description holding lock */
struct lockf **lf_head; /* Back pointer to the head of lockf list */
struct lockf *lf_next; /* Next lock on this vnode, or blocking lock */
struct locklist lf_blkhd; /* List of requests blocked on this lock */
TAILQ_ENTRY(lockf) lf_block;/* A request waiting for a lock */
struct uidinfo *lf_uip; /* Cached pointer to uidinfo */
};
/* Maximum length of sleep chains to traverse to try and detect deadlock. */
#define MAXDEPTH 50
/*
* This variable controls the maximum number of processes that will
* be checked in doing deadlock detection.
*/
int maxlockdepth = MAXDEPTH;
#ifdef LOCKF_DEBUG
int lockf_debug = 0;
#endif
#define SELF 0x1
#define OTHERS 0x2
/*
* XXX TODO
* Misc cleanups: "void *id" should be visible in the API as a
* "struct proc *".
* (This requires rototilling all VFS's which support advisory locking).
*/
/*
* If there's a lot of lock contention on a single vnode, locking
* schemes which allow for more paralleism would be needed. Given how
* infrequently byte-range locks are actually used in typical BSD
* code, a more complex approach probably isn't worth it.
*/
/*
* We enforce a limit on locks by uid, so that a single user cannot
* run the kernel out of memory. For now, the limit is pretty coarse.
* There is no limit on root.
*
* Splitting a lock will always succeed, regardless of current allocations.
* If you're slightly above the limit, we still have to permit an allocation
* so that the unlock can succeed. If the unlocking causes too many splits,
* however, you're totally cutoff.
*/
#define MAXLOCKSPERUID (2 * maxfiles)
#ifdef LOCKF_DEBUG
/*
* Print out a lock.
*/
static void
lf_print(const char *tag, struct lockf *lock)
{
/*
* Walk the list of locks for an inode to
* find an overlapping lock (if any).
*
* NOTE: this returns only the FIRST overlapping lock. There
* may be more than one.
*/
static int
lf_findoverlap(struct lockf *lf, struct lockf *lock, int type,
struct lockf ***prev, struct lockf **overlap)
{
off_t start, end;
/*
* Split a lock and a contained region into
* two or three locks as necessary.
*/
static void
lf_split(struct lockf *lock1, struct lockf *lock2, struct lockf **sparelock)
{
struct lockf *splitlock;
#ifdef LOCKF_DEBUG
if (lockf_debug & 2) {
lf_print("lf_split", lock1);
lf_print("splitting from", lock2);
}
#endif /* LOCKF_DEBUG */
/*
* Check to see if splitting into only two pieces.
*/
if (lock1->lf_start == lock2->lf_start) {
lock1->lf_start = lock2->lf_end + 1;
lock2->lf_next = lock1;
return;
}
if (lock1->lf_end == lock2->lf_end) {
lock1->lf_end = lock2->lf_start - 1;
lock2->lf_next = lock1->lf_next;
lock1->lf_next = lock2;
return;
}
/*
* Make a new lock consisting of the last part of
* the encompassing lock
*/
splitlock = *sparelock;
*sparelock = NULL;
cv_destroy(&splitlock->lf_cv);
memcpy(splitlock, lock1, sizeof(*splitlock));
cv_init(&splitlock->lf_cv, lockstr);
splitlock->lf_start = lock2->lf_end + 1;
TAILQ_INIT(&splitlock->lf_blkhd);
lock1->lf_end = lock2->lf_start - 1;
/*
* OK, now link it in
*/
splitlock->lf_next = lock1->lf_next;
lock2->lf_next = splitlock;
lock1->lf_next = lock2;
}
/*
* Remove a byte-range lock on an inode.
*
* Generally, find the lock (or an overlap to that lock)
* and remove it (or shrink it), then wakeup anyone we can.
*/
static int
lf_clearlock(struct lockf *unlock, struct lockf **sparelock)
{
struct lockf **head = unlock->lf_head;
struct lockf *lf = *head;
struct lockf *overlap, **prev;
int ovcase;
if (lf == NULL)
return 0;
#ifdef LOCKF_DEBUG
if (unlock->lf_type != F_UNLCK)
panic("lf_clearlock: bad type");
if (lockf_debug & 1)
lf_print("lf_clearlock", unlock);
#endif /* LOCKF_DEBUG */
prev = head;
while ((ovcase = lf_findoverlap(lf, unlock, SELF,
&prev, &overlap)) != 0) {
/*
* Wakeup the list of locks to be retried.
*/
lf_wakelock(overlap);
/*
* Walk the list of locks for an inode and
* return the first blocking lock.
*/
static struct lockf *
lf_getblock(struct lockf *lock)
{
struct lockf **prev, *overlap, *lf = *(lock->lf_head);
prev = lock->lf_head;
while (lf_findoverlap(lf, lock, OTHERS, &prev, &overlap) != 0) {
/*
* We've found an overlap, see if it blocks us
*/
if ((lock->lf_type == F_WRLCK || overlap->lf_type == F_WRLCK))
return overlap;
/*
* Nope, point to the next one on the list and
* see if it blocks us
*/
lf = overlap->lf_next;
}
return NULL;
}
/*
* Set a byte-range lock.
*/
static int
lf_setlock(struct lockf *lock, struct lockf **sparelock,
kmutex_t *interlock)
{
struct lockf *block;
struct lockf **head = lock->lf_head;
struct lockf **prev, *overlap, *ltmp;
int ovcase, needtolink, error;
/*
* Scan lock list for this file looking for locks that would block us.
*/
while ((block = lf_getblock(lock)) != NULL) {
/*
* Free the structure and return if nonblocking.
*/
if ((lock->lf_flags & F_WAIT) == 0) {
lf_free(lock);
return SET_ERROR(EAGAIN);
}
/*
* We are blocked. Since flock style locks cover
* the whole file, there is no chance for deadlock.
* For byte-range locks we must check for deadlock.
*
* Deadlock detection is done by looking through the
* wait channels to see if there are any cycles that
* involve us. MAXDEPTH is set just to make sure we
* do not go off into neverneverland.
*/
if ((lock->lf_flags & F_POSIX) &&
(block->lf_flags & F_POSIX)) {
struct lwp *wlwp;
volatile const struct lockf *waitblock;
int i = 0;
struct proc *p;
p = (struct proc *)block->lf_id;
KASSERT(p != NULL);
while (i++ < maxlockdepth) {
mutex_enter(p->p_lock);
if (p->p_nlwps > 1) {
mutex_exit(p->p_lock);
break;
}
wlwp = LIST_FIRST(&p->p_lwps);
lwp_lock(wlwp);
if (wlwp->l_wchan == NULL ||
wlwp->l_wmesg != lockstr) {
lwp_unlock(wlwp);
mutex_exit(p->p_lock);
break;
}
waitblock = wlwp->l_wchan;
lwp_unlock(wlwp);
mutex_exit(p->p_lock);
/* Get the owner of the blocking lock */
waitblock = waitblock->lf_next;
if ((waitblock->lf_flags & F_POSIX) == 0)
break;
p = (struct proc *)waitblock->lf_id;
if (p == curproc) {
lf_free(lock);
return SET_ERROR(EDEADLK);
}
}
/*
* If we're still following a dependency chain
* after maxlockdepth iterations, assume we're in
* a cycle to be safe.
*/
if (i >= maxlockdepth) {
lf_free(lock);
return SET_ERROR(EDEADLK);
}
}
/*
* For flock type locks, we must first remove
* any shared locks that we hold before we sleep
* waiting for an exclusive lock.
*/
if ((lock->lf_flags & F_FLOCK) &&
lock->lf_type == F_WRLCK) {
lock->lf_type = F_UNLCK;
(void) lf_clearlock(lock, NULL);
lock->lf_type = F_WRLCK;
}
/*
* Add our lock to the blocked list and sleep until we're free.
* Remember who blocked us (for deadlock detection).
*/
lock->lf_next = block;
TAILQ_INSERT_TAIL(&block->lf_blkhd, lock, lf_block);
#ifdef LOCKF_DEBUG
if (lockf_debug & 1) {
lf_print("lf_setlock: blocking on", block);
lf_printlist("lf_setlock", block);
}
#endif /* LOCKF_DEBUG */
error = cv_wait_sig(&lock->lf_cv, interlock);
/*
* We may have been awoken by a signal (in
* which case we must remove ourselves from the
* blocked list) and/or by another process
* releasing a lock (in which case we have already
* been removed from the blocked list and our
* lf_next field set to NULL).
*/
if (lock->lf_next != NULL) {
TAILQ_REMOVE(&lock->lf_next->lf_blkhd, lock, lf_block);
lock->lf_next = NULL;
}
if (error) {
lf_free(lock);
return error;
}
}
/*
* No blocks!! Add the lock. Note that we will
* downgrade or upgrade any overlapping locks this
* process already owns.
*
* Skip over locks owned by other processes.
* Handle any locks that overlap and are owned by ourselves.
*/
prev = head;
block = *head;
needtolink = 1;
for (;;) {
ovcase = lf_findoverlap(block, lock, SELF, &prev, &overlap);
if (ovcase)
block = overlap->lf_next;
/*
* Six cases:
* 0) no overlap
* 1) overlap == lock
* 2) overlap contains lock
* 3) lock contains overlap
* 4) overlap starts before lock
* 5) overlap ends after lock
*/
switch (ovcase) {
case 0: /* no overlap */
if (needtolink) {
*prev = lock;
lock->lf_next = overlap;
}
break;
case 1: /* overlap == lock */
/*
* If downgrading lock, others may be
* able to acquire it.
*/
if (lock->lf_type == F_RDLCK &&
overlap->lf_type == F_WRLCK)
lf_wakelock(overlap);
overlap->lf_type = lock->lf_type;
lf_free(lock);
lock = overlap; /* for debug output below */
break;
case 2: /* overlap contains lock */
/*
* Check for common starting point and different types.
*/
if (overlap->lf_type == lock->lf_type) {
lf_free(lock);
lock = overlap; /* for debug output below */
break;
}
if (overlap->lf_start == lock->lf_start) {
*prev = lock;
lock->lf_next = overlap;
overlap->lf_start = lock->lf_end + 1;
} else
lf_split(overlap, lock, sparelock);
lf_wakelock(overlap);
break;
case 3: /* lock contains overlap */
/*
* If downgrading lock, others may be able to
* acquire it, otherwise take the list.
*/
if (lock->lf_type == F_RDLCK &&
overlap->lf_type == F_WRLCK) {
lf_wakelock(overlap);
} else {
while ((ltmp =
TAILQ_FIRST(&overlap->lf_blkhd))
!= NULL) {
KASSERT(ltmp->lf_next == overlap);
TAILQ_REMOVE(&overlap->lf_blkhd, ltmp,
lf_block);
ltmp->lf_next = lock;
TAILQ_INSERT_TAIL(&lock->lf_blkhd,
ltmp, lf_block);
}
}
/*
* Add the new lock if necessary and delete the
* overlap.
*/
if (needtolink) {
*prev = lock;
lock->lf_next = overlap->lf_next;
prev = &lock->lf_next;
needtolink = 0;
} else
*prev = overlap->lf_next;
lf_free(overlap);
continue;
case 4: /* overlap starts before lock */
/*
* Add lock after overlap on the list.
*/
lock->lf_next = overlap->lf_next;
overlap->lf_next = lock;
overlap->lf_end = lock->lf_start - 1;
prev = &lock->lf_next;
lf_wakelock(overlap);
needtolink = 0;
continue;
case 5: /* overlap ends after lock */
/*
* Add the new lock before overlap.
*/
if (needtolink) {
*prev = lock;
lock->lf_next = overlap;
}
overlap->lf_start = lock->lf_end + 1;
lf_wakelock(overlap);
break;
}
break;
}
#ifdef LOCKF_DEBUG
if (lockf_debug & 1) {
lf_print("lf_setlock: got the lock", lock);
lf_printlist("lf_setlock", lock);
}
#endif /* LOCKF_DEBUG */
return 0;
}
/*
* Check whether there is a blocking lock,
* and if so return its process identifier.
*/
static int
lf_getlock(struct lockf *lock, struct flock *fl)
{
struct lockf *block;
/*
* Convert the flock structure into a start and end.
*/
switch (fl->l_whence) {
case SEEK_SET:
case SEEK_CUR:
/*
* Caller is responsible for adding any necessary offset
* when SEEK_CUR is used.
*/
start = fl->l_start;
break;
case SEEK_END:
if (fl->l_start > __type_max(off_t) - size)
return SET_ERROR(EINVAL);
start = size + fl->l_start;
break;
default:
return SET_ERROR(EINVAL);
}
if (fl->l_len == 0)
end = -1;
else {
if (fl->l_len >= 0) {
if (start >= 0 &&
fl->l_len - 1 > __type_max(off_t) - start)
return SET_ERROR(EINVAL);
end = start + (fl->l_len - 1);
} else {
/* lockf() allows -ve lengths */
if (start < 0)
return SET_ERROR(EINVAL);
end = start - 1;
start += fl->l_len;
}
}
if (start < 0)
return SET_ERROR(EINVAL);
/*
* Allocate locks before acquiring the interlock. We need two
* locks in the worst case.
*/
switch (ap->a_op) {
case F_SETLK:
case F_UNLCK:
/*
* XXX For F_UNLCK case, we can re-use the lock.
*/
if ((ap->a_flags & F_FLOCK) == 0) {
/*
* Byte-range lock might need one more lock.
*/
sparelock = lf_alloc(0);
if (sparelock == NULL) {
error = SET_ERROR(ENOMEM);
goto quit;
}
break;
}
/* FALLTHROUGH */
case F_GETLK:
sparelock = NULL;
break;
default:
return SET_ERROR(EINVAL);
}
switch (ap->a_op) {
case F_SETLK:
lock = lf_alloc(1);
break;
case F_UNLCK:
if (start == 0 || end == -1) {
/* never split */
lock = lf_alloc(0);
} else {
/* might split */
lock = lf_alloc(2);
}
break;
case F_GETLK:
lock = lf_alloc(0);
break;
}
if (lock == NULL) {
error = SET_ERROR(ENOMEM);
goto quit;
}
mutex_enter(interlock);
/*
* Avoid the common case of unlocking when inode has no locks.
*/
if (*head == (struct lockf *)0) {
if (ap->a_op != F_SETLK) {
fl->l_type = F_UNLCK;
error = 0;
goto quit_unlock;
}
}
/*
* Do the requested operation.
*/
switch (ap->a_op) {
case F_SETLK:
error = lf_setlock(lock, &sparelock, interlock);
lock = NULL; /* lf_setlock freed it */
break;
case F_UNLCK:
error = lf_clearlock(lock, &sparelock);
break;
case F_GETLK:
error = lf_getlock(lock, fl);
break;
default:
break;
/* NOTREACHED */
}
quit_unlock:
mutex_exit(interlock);
quit:
if (lock)
lf_free(lock);
if (sparelock)
lf_free(sparelock);
return error;
}
/*
* Initialize subsystem.
*
* XXX We use a global lock. This could be the vnode interlock, but
* the deadlock detection code may need to inspect locks belonging to
* other files.
*/
void
lf_init(void)
{
