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 /*
  52  * Interlocked wait against a decrement-to-0 (sans the REFCNTF_WAITING flag).
  53  *
  54  * Users of this waiting API must use refcount_release_wakeup() to release
  55  * refs instead of refcount_release().  refcount_release() will not wake
  56  * up waiters.
  57  */
  58 void
  59 _refcount_wait(volatile u_int *countp, const char *wstr)
  60 {
  61         u_int n;
  62         int base_ticks = ticks;
  63
  64         n = *countp;
  65         for (;;) {
  66                 cpu_ccfence();
  67                 if ((n & ~REFCNTF_WAITING) == 0)
  68                         break;
  69                 if ((int)(ticks - base_ticks) >= hz*60 - 1) {
  70                         kprintf("warning: refcount_wait %s: long wait\n", wstr);
  71                         base_ticks = ticks;
  72                 }
  73                 tsleep_interlock(countp, 0);
  74                 if (atomic_fcmpset_int(countp, &n, n | REFCNTF_WAITING))
  75                         tsleep(countp, PINTERLOCKED, wstr, hz*10);
  76         }
  77 }