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 loops = 0; 69 int threshold = 5; 70 71 for (;;) { 72 n = *countp; 73 if (n == 0) 74 break; 75 if (loops > threshold) { 76 kprintf("refcount_wait %s long wait\n", wstr); 77 loops = 0; 78 } 79 KKASSERT(n != REFCNTF_WAITING); /* impossible state */ 80 tsleep_interlock(countp, 0); 81 if (atomic_cmpset_int(countp, n, n | REFCNTF_WAITING)) 82 tsleep(countp, PINTERLOCKED, wstr, hz*10); 83 loops++; 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 1->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 1 and leave the REFCNTF_WAITING 95 * 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 int 101 _refcount_release_wakeup(volatile u_int *countp) 102 { 103 u_int n; 104 105 for (;;) { 106 n = *countp; 107 if (n == (REFCNTF_WAITING | 1)) { 108 if (atomic_cmpset_int(countp, n, 0)) { 109 wakeup(countp); 110 n = 1; 111 break; 112 } 113 } else { 114 KKASSERT(n != REFCNTF_WAITING); /* illegal state */ 115 if (atomic_cmpset_int(countp, n, n - 1)) 116 break; 117 } 118 } 119 return (n == 1); 120 } 121