sys/kern/kern_refcount.c

   1 /*
   2  * Copyright (c) 2011 The DragonFly Project.  All rights reserved.
   3  *
   4  * This code is derived from software contributed to The DragonFly Project
   5  * by Matthew Dillon <dillon@backplane.com>
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  *
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice, this list of conditions and the following disclaimer.
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in
  15  *    the documentation and/or other materials provided with the
  16  *    distribution.
  17  * 3. Neither the name of The DragonFly Project nor the names of its
  18  *    contributors may be used to endorse or promote products derived
  19  *    from this software without specific, prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  22  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  23  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  24  * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
  25  * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  26  * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
  27  * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  28  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
  29  * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  30  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
  31  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  */
  34 /*
  35  * Implement helper routines for the refcount inlines in sys/refcount.h.
  36  *
  37  * These helpers implement the refcount_release_wakeup() and refcount_wait()
  38  * APIs for the non-trivial or race case.  The trivial non-race case is
  39  * handled by the inline in sys/refcount.h
  40  */
  41
  42 #include <sys/param.h>
  43 #include <sys/systm.h>
  44 #include <sys/kernel.h>
  45 #include <sys/sysctl.h>
  46 #include <sys/thread.h>
  47 #include <sys/refcount.h>
  48
  49 #include <machine/cpufunc.h>
  50
  51 #include <sys/thread2.h>
  52
  53 /*
  54  * Helper function to wait for a reference count to become zero.
  55  * We set REFCNTF_WAITING and sleep if the reference count is not zero.
  56  *
  57  * In the case where REFCNTF_WAITING is already set the atomic op validates
  58  * that it is still set after the tsleep_interlock() call.
  59  *
  60  * Users of this waiting API must use refcount_release_wakeup() to release
  61  * refs instead of refcount_release().  refcount_release() will not wake
  62  * up waiters.
  63  */
  64 void
  65 _refcount_wait(volatile u_int *countp, const char *wstr)
  66 {
  67         u_int n;
  68         int base_ticks = ticks;
  69
  70         for (;;) {
  71                 n = *countp;
  72                 cpu_ccfence();
  73                 if (n == 0)
  74                         break;
  75                 if ((int)(ticks - base_ticks) >= hz*60 - 1) {
  76                         kprintf("warning: refcount_wait %s: long wait\n",
  77                                 wstr);
  78                         base_ticks = ticks;
  79                 }
  80                 KKASSERT(n != REFCNTF_WAITING); /* impossible state */
  81                 tsleep_interlock(countp, 0);
  82                 if (atomic_cmpset_int(countp, n, n | REFCNTF_WAITING))
  83                         tsleep(countp, PINTERLOCKED, wstr, hz*10);
  84         }
  85 }
  86
  87 /*
  88  * This helper function implements the release-with-wakeup API.  It is
  89  * executed for the non-trivial case or if the atomic op races.
  90  *
  91  * On the i->0 transition is REFCNTF_WAITING is set it will be cleared
  92  * and a wakeup() will be issued.
  93  *
  94  * On any other transition we simply subtract (i) and leave the
  95  * REFCNTF_WAITING flag intact.
  96  *
  97  * This function returns TRUE(1) on the last release, whether a wakeup
  98  * occured or not, and FALSE(0) otherwise.
  99  *
 100  * NOTE!  (i) cannot be 0
 101  */
 102 int
 103 _refcount_release_wakeup_n(volatile u_int *countp, u_int i)
 104 {
 105         u_int n;
 106
 107         for (;;) {
 108                 n = *countp;
 109                 cpu_ccfence();
 110                 if (n == (REFCNTF_WAITING | i)) {
 111                         if (atomic_cmpset_int(countp, n, 0)) {
 112                                 wakeup(countp);
 113                                 n = i;
 114                                 break;
 115                         }
 116                 } else {
 117                         KKASSERT(n != REFCNTF_WAITING); /* illegal state */
 118                         if (atomic_cmpset_int(countp, n, n - i))
 119                                 break;
 120                 }
 121         }
 122         return (n == i);
 123 }