1 /* 2 * Copyright (c) 2003,2004 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> and David Xu <davidxu@freebsd.org> 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 * $DragonFly: src/sys/kern/kern_umtx.c,v 1.9 2008/05/09 07:24:45 dillon Exp $ 35 */ 36 37 /* 38 * This module implements userland mutex helper functions. umtx_sleep() 39 * handling blocking and umtx_wakeup() handles wakeups. The sleep/wakeup 40 * functions operate on user addresses. 41 */ 42 43 #include <sys/param.h> 44 #include <sys/systm.h> 45 #include <sys/kernel.h> 46 #include <sys/sysproto.h> 47 #include <sys/sysunion.h> 48 #include <sys/sysent.h> 49 #include <sys/syscall.h> 50 #include <sys/module.h> 51 52 #include <cpu/lwbuf.h> 53 54 #include <vm/vm.h> 55 #include <vm/vm_param.h> 56 #include <sys/lock.h> 57 #include <vm/pmap.h> 58 #include <vm/vm_map.h> 59 #include <vm/vm_object.h> 60 #include <vm/vm_page.h> 61 #include <vm/vm_pager.h> 62 #include <vm/vm_pageout.h> 63 #include <vm/vm_extern.h> 64 #include <vm/vm_page.h> 65 #include <vm/vm_kern.h> 66 67 #include <vm/vm_page2.h> 68 #include <sys/mplock2.h> 69 70 static void umtx_sleep_page_action_cow(vm_page_t m, vm_page_action_t action); 71 72 /* 73 * If the contents of the userland-supplied pointer matches the specified 74 * value enter an interruptable sleep for up to <timeout> microseconds. 75 * If the contents does not match then return immediately. 76 * 77 * Returns 0 if we slept and were woken up, -1 and EWOULDBLOCK if we slept 78 * and timed out, and EBUSY if the contents of the pointer already does 79 * not match the specified value. A timeout of 0 indicates an unlimited sleep. 80 * EINTR is returned if the call was interrupted by a signal (even if 81 * the signal specifies that the system call should restart). 82 * 83 * This function interlocks against call to umtx_wakeup. It does NOT interlock 84 * against changes in *ptr. However, it does not have to. The standard use 85 * of *ptr is to differentiate between an uncontested and a contested mutex 86 * and call umtx_wakeup when releasing a contested mutex. Therefore we can 87 * safely race against changes in *ptr as long as we are properly interlocked 88 * against the umtx_wakeup() call. 89 * 90 * The VM page associated with the mutex is held in an attempt to keep 91 * the mutex's physical address consistent, allowing umtx_sleep() and 92 * umtx_wakeup() to use the physical address as their rendezvous. BUT 93 * situations can arise where the physical address may change, particularly 94 * if a threaded program fork()'s and the mutex's memory becomes 95 * copy-on-write. We register an event on the VM page to catch COWs. 96 * 97 * umtx_sleep { const int *ptr, int value, int timeout } 98 * 99 * MPALMOSTSAFE 100 */ 101 int 102 sys_umtx_sleep(struct umtx_sleep_args *uap) 103 { 104 int error = EBUSY; 105 struct lwbuf *lwb; 106 struct vm_page_action action; 107 vm_page_t m; 108 void *waddr; 109 int offset; 110 int timeout; 111 112 if (uap->timeout < 0) 113 return (EINVAL); 114 if ((vm_offset_t)uap->ptr & (sizeof(int) - 1)) 115 return (EFAULT); 116 117 /* 118 * When faulting in the page, force any COW pages to be resolved. 119 * Otherwise the physical page we sleep on my not match the page 120 * being woken up. 121 */ 122 get_mplock(); 123 m = vm_fault_page_quick((vm_offset_t)uap->ptr, VM_PROT_READ|VM_PROT_WRITE, &error); 124 if (m == NULL) { 125 error = EFAULT; 126 goto done; 127 } 128 lwb = lwbuf_alloc(m); 129 offset = (vm_offset_t)uap->ptr & PAGE_MASK; 130 131 /* 132 * The critical section is required to interlock the tsleep against 133 * a wakeup from another cpu. The lfence forces synchronization. 134 */ 135 if (*(int *)(lwbuf_kva(lwb) + offset) == uap->value) { 136 if ((timeout = uap->timeout) != 0) { 137 timeout = (timeout / 1000000) * hz + 138 ((timeout % 1000000) * hz + 999999) / 1000000; 139 } 140 waddr = (void *)((intptr_t)VM_PAGE_TO_PHYS(m) + offset); 141 crit_enter(); 142 tsleep_interlock(waddr, PCATCH | PDOMAIN_UMTX); 143 if (*(int *)(lwbuf_kva(lwb) + offset) == uap->value) { 144 vm_page_init_action(&action, umtx_sleep_page_action_cow, waddr); 145 vm_page_register_action(m, &action, VMEVENT_COW); 146 error = tsleep(waddr, PCATCH | PINTERLOCKED | PDOMAIN_UMTX, 147 "umtxsl", timeout); 148 vm_page_unregister_action(m, &action); 149 } else { 150 error = EBUSY; 151 } 152 crit_exit(); 153 /* Always break out in case of signal, even if restartable */ 154 if (error == ERESTART) 155 error = EINTR; 156 } else { 157 error = EBUSY; 158 } 159 160 lwbuf_free(lwb); 161 /*vm_page_dirty(m); we don't actually dirty the page */ 162 vm_page_unhold(m); 163 done: 164 rel_mplock(); 165 return(error); 166 } 167 168 /* 169 * If this page is being copied it may no longer represent the page 170 * underlying our virtual address. Wake up any umtx_sleep()'s 171 * that were waiting on its physical address to force them to retry. 172 */ 173 static void 174 umtx_sleep_page_action_cow(vm_page_t m, vm_page_action_t action) 175 { 176 wakeup_domain(action->data, PDOMAIN_UMTX); 177 } 178 179 /* 180 * umtx_wakeup { const int *ptr, int count } 181 * 182 * Wakeup the specified number of processes held in umtx_sleep() on the 183 * specified user address. A count of 0 wakes up all waiting processes. 184 * 185 * XXX assumes that the physical address space does not exceed the virtual 186 * address space. 187 * 188 * MPALMOSTSAFE 189 */ 190 int 191 sys_umtx_wakeup(struct umtx_wakeup_args *uap) 192 { 193 vm_page_t m; 194 int offset; 195 int error; 196 void *waddr; 197 198 cpu_mfence(); 199 if ((vm_offset_t)uap->ptr & (sizeof(int) - 1)) 200 return (EFAULT); 201 get_mplock(); 202 m = vm_fault_page_quick((vm_offset_t)uap->ptr, VM_PROT_READ, &error); 203 if (m == NULL) { 204 error = EFAULT; 205 goto done; 206 } 207 offset = (vm_offset_t)uap->ptr & PAGE_MASK; 208 waddr = (void *)((intptr_t)VM_PAGE_TO_PHYS(m) + offset); 209 210 if (uap->count == 1) { 211 wakeup_domain_one(waddr, PDOMAIN_UMTX); 212 } else { 213 /* XXX wakes them all up for now */ 214 wakeup_domain(waddr, PDOMAIN_UMTX); 215 } 216 vm_page_unhold(m); 217 error = 0; 218 done: 219 rel_mplock(); 220 return(error); 221 } 222 223