The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_rangelock.c

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    1 /*-
    2  * Copyright (c) 2009 Konstantin Belousov <kib@FreeBSD.org>
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice unmodified, this list of conditions, and the following
   10  *    disclaimer.
   11  * 2. Redistributions in binary form must reproduce the above copyright
   12  *    notice, this list of conditions and the following disclaimer in the
   13  *    documentation and/or other materials provided with the distribution.
   14  *
   15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
   16  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   17  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
   18  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
   19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   20  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
   21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
   22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
   23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
   24  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   25  */
   26 
   27 #include <sys/cdefs.h>
   28 __FBSDID("$FreeBSD: stable/10/sys/kern/kern_rangelock.c 254380 2013-08-15 20:19:17Z cperciva $");
   29 
   30 #include <sys/param.h>
   31 #include <sys/kernel.h>
   32 #include <sys/lock.h>
   33 #include <sys/mutex.h>
   34 #include <sys/proc.h>
   35 #include <sys/rangelock.h>
   36 #include <sys/systm.h>
   37 
   38 #include <vm/uma.h>
   39 
   40 struct rl_q_entry {
   41         TAILQ_ENTRY(rl_q_entry) rl_q_link;
   42         off_t           rl_q_start, rl_q_end;
   43         int             rl_q_flags;
   44 };
   45 
   46 static uma_zone_t rl_entry_zone;
   47 
   48 static void
   49 rangelock_sys_init(void)
   50 {
   51 
   52         rl_entry_zone = uma_zcreate("rl_entry", sizeof(struct rl_q_entry),
   53             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
   54 }
   55 SYSINIT(vfs, SI_SUB_LOCK, SI_ORDER_ANY, rangelock_sys_init, NULL);
   56 
   57 static struct rl_q_entry *
   58 rlqentry_alloc(void)
   59 {
   60 
   61         return (uma_zalloc(rl_entry_zone, M_WAITOK));
   62 }
   63 
   64 void
   65 rlqentry_free(struct rl_q_entry *rleq)
   66 {
   67 
   68         uma_zfree(rl_entry_zone, rleq);
   69 }
   70 
   71 void
   72 rangelock_init(struct rangelock *lock)
   73 {
   74 
   75         TAILQ_INIT(&lock->rl_waiters);
   76         lock->rl_currdep = NULL;
   77 }
   78 
   79 void
   80 rangelock_destroy(struct rangelock *lock)
   81 {
   82 
   83         KASSERT(TAILQ_EMPTY(&lock->rl_waiters), ("Dangling waiters"));
   84 }
   85 
   86 /*
   87  * Two entries are compatible if their ranges do not overlap, or both
   88  * entries are for read.
   89  */
   90 static int
   91 ranges_overlap(const struct rl_q_entry *e1,
   92     const struct rl_q_entry *e2)
   93 {
   94 
   95         if (e1->rl_q_start < e2->rl_q_end && e1->rl_q_end > e2->rl_q_start)
   96                 return (1);
   97         return (0);
   98 }
   99 
  100 /*
  101  * Recalculate the lock->rl_currdep after an unlock.
  102  */
  103 static void
  104 rangelock_calc_block(struct rangelock *lock)
  105 {
  106         struct rl_q_entry *entry, *nextentry, *entry1;
  107 
  108         for (entry = lock->rl_currdep; entry != NULL; entry = nextentry) {
  109                 nextentry = TAILQ_NEXT(entry, rl_q_link);
  110                 if (entry->rl_q_flags & RL_LOCK_READ) {
  111                         /* Reads must not overlap with granted writes. */
  112                         for (entry1 = TAILQ_FIRST(&lock->rl_waiters);
  113                             !(entry1->rl_q_flags & RL_LOCK_READ);
  114                             entry1 = TAILQ_NEXT(entry1, rl_q_link)) {
  115                                 if (ranges_overlap(entry, entry1))
  116                                         goto out;
  117                         }
  118                 } else {
  119                         /* Write must not overlap with any granted locks. */
  120                         for (entry1 = TAILQ_FIRST(&lock->rl_waiters);
  121                             entry1 != entry;
  122                             entry1 = TAILQ_NEXT(entry1, rl_q_link)) {
  123                                 if (ranges_overlap(entry, entry1))
  124                                         goto out;
  125                         }
  126 
  127                         /* Move grantable write locks to the front. */
  128                         TAILQ_REMOVE(&lock->rl_waiters, entry, rl_q_link);
  129                         TAILQ_INSERT_HEAD(&lock->rl_waiters, entry, rl_q_link);
  130                 }
  131 
  132                 /* Grant this lock. */
  133                 entry->rl_q_flags |= RL_LOCK_GRANTED;
  134                 wakeup(entry);
  135         }
  136 out:
  137         lock->rl_currdep = entry;
  138 }
  139 
  140 static void
  141 rangelock_unlock_locked(struct rangelock *lock, struct rl_q_entry *entry,
  142     struct mtx *ilk)
  143 {
  144 
  145         MPASS(lock != NULL && entry != NULL && ilk != NULL);
  146         mtx_assert(ilk, MA_OWNED);
  147         KASSERT(entry != lock->rl_currdep, ("stuck currdep"));
  148 
  149         TAILQ_REMOVE(&lock->rl_waiters, entry, rl_q_link);
  150         rangelock_calc_block(lock);
  151         mtx_unlock(ilk);
  152         if (curthread->td_rlqe == NULL)
  153                 curthread->td_rlqe = entry;
  154         else
  155                 rlqentry_free(entry);
  156 }
  157 
  158 void
  159 rangelock_unlock(struct rangelock *lock, void *cookie, struct mtx *ilk)
  160 {
  161 
  162         MPASS(lock != NULL && cookie != NULL && ilk != NULL);
  163 
  164         mtx_lock(ilk);
  165         rangelock_unlock_locked(lock, cookie, ilk);
  166 }
  167 
  168 /*
  169  * Unlock the sub-range of granted lock.
  170  */
  171 void *
  172 rangelock_unlock_range(struct rangelock *lock, void *cookie, off_t start,
  173     off_t end, struct mtx *ilk)
  174 {
  175         struct rl_q_entry *entry;
  176 
  177         MPASS(lock != NULL && cookie != NULL && ilk != NULL);
  178         entry = cookie;
  179         KASSERT(entry->rl_q_flags & RL_LOCK_GRANTED,
  180             ("Unlocking non-granted lock"));
  181         KASSERT(entry->rl_q_start == start, ("wrong start"));
  182         KASSERT(entry->rl_q_end >= end, ("wrong end"));
  183 
  184         mtx_lock(ilk);
  185         if (entry->rl_q_end == end) {
  186                 rangelock_unlock_locked(lock, cookie, ilk);
  187                 return (NULL);
  188         }
  189         entry->rl_q_end = end;
  190         rangelock_calc_block(lock);
  191         mtx_unlock(ilk);
  192         return (cookie);
  193 }
  194 
  195 /*
  196  * Add the lock request to the queue of the pending requests for
  197  * rangelock.  Sleep until the request can be granted.
  198  */
  199 static void *
  200 rangelock_enqueue(struct rangelock *lock, off_t start, off_t end, int mode,
  201     struct mtx *ilk)
  202 {
  203         struct rl_q_entry *entry;
  204         struct thread *td;
  205 
  206         MPASS(lock != NULL && ilk != NULL);
  207 
  208         td = curthread;
  209         if (td->td_rlqe != NULL) {
  210                 entry = td->td_rlqe;
  211                 td->td_rlqe = NULL;
  212         } else
  213                 entry = rlqentry_alloc();
  214         MPASS(entry != NULL);
  215         entry->rl_q_flags = mode;
  216         entry->rl_q_start = start;
  217         entry->rl_q_end = end;
  218 
  219         mtx_lock(ilk);
  220         /*
  221          * XXXKIB TODO. Check that a thread does not try to enqueue a
  222          * lock that is incompatible with another request from the same
  223          * thread.
  224          */
  225 
  226         TAILQ_INSERT_TAIL(&lock->rl_waiters, entry, rl_q_link);
  227         if (lock->rl_currdep == NULL)
  228                 lock->rl_currdep = entry;
  229         rangelock_calc_block(lock);
  230         while (!(entry->rl_q_flags & RL_LOCK_GRANTED))
  231                 msleep(entry, ilk, 0, "range", 0);
  232         mtx_unlock(ilk);
  233         return (entry);
  234 }
  235 
  236 void *
  237 rangelock_rlock(struct rangelock *lock, off_t start, off_t end, struct mtx *ilk)
  238 {
  239 
  240         return (rangelock_enqueue(lock, start, end, RL_LOCK_READ, ilk));
  241 }
  242 
  243 void *
  244 rangelock_wlock(struct rangelock *lock, off_t start, off_t end, struct mtx *ilk)
  245 {
  246 
  247         return (rangelock_enqueue(lock, start, end, RL_LOCK_WRITE, ilk));
  248 }

Cache object: 9969220b085c80b813670efd42c36f17


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