1 /* 2 * Copyright (c) 2003,2004,2010,2017 The DragonFly Project. 3 * All rights reserved. 4 * 5 * This code is derived from software contributed to The DragonFly Project 6 * by Matthew Dillon <dillon@backplane.com> and David Xu <davidxu@freebsd.org> 7 * 8 * Redistribution and use in source and binary forms, with or without 9 * modification, are permitted provided that the following conditions 10 * are met: 11 * 12 * 1. Redistributions of source code must retain the above copyright 13 * notice, this list of conditions and the following disclaimer. 14 * 2. Redistributions in binary form must reproduce the above copyright 15 * notice, this list of conditions and the following disclaimer in 16 * the documentation and/or other materials provided with the 17 * distribution. 18 * 3. Neither the name of The DragonFly Project nor the names of its 19 * contributors may be used to endorse or promote products derived 20 * from this software without specific, prior written permission. 21 * 22 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 23 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 24 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 25 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 26 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 27 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING, 28 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 29 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 30 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 31 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 32 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33 * SUCH DAMAGE. 34 */ 35 36 /* 37 * This module implements userland mutex helper functions. umtx_sleep() 38 * handling blocking and umtx_wakeup() handles wakeups. The sleep/wakeup 39 * functions operate on user addresses. 40 */ 41 42 #include <sys/param.h> 43 #include <sys/systm.h> 44 #include <sys/cdefs.h> 45 #include <sys/kernel.h> 46 #include <sys/sysmsg.h> 47 #include <sys/sysent.h> 48 #include <sys/syscall.h> 49 #include <sys/sysctl.h> 50 #include <sys/module.h> 51 #include <sys/thread.h> 52 #include <sys/proc.h> 53 54 #include <cpu/lwbuf.h> 55 56 #include <vm/vm.h> 57 #include <vm/vm_param.h> 58 #include <sys/lock.h> 59 #include <vm/pmap.h> 60 #include <vm/vm_map.h> 61 #include <vm/vm_object.h> 62 #include <vm/vm_page.h> 63 #include <vm/vm_pager.h> 64 #include <vm/vm_pageout.h> 65 #include <vm/vm_extern.h> 66 #include <vm/vm_kern.h> 67 68 #include <vm/vm_page2.h> 69 70 /* 71 * Improve umtx performance by polling for 4000nS before going to sleep. 72 * This can avoid many IPIs in typical pthreads mutex situations. 73 */ 74 #ifdef _RDTSC_SUPPORTED_ 75 static int umtx_delay = 4000; /* nS */ 76 SYSCTL_INT(_kern, OID_AUTO, umtx_delay, CTLFLAG_RW, 77 &umtx_delay, 0, ""); 78 #endif 79 static int umtx_timeout_max = 2000000; /* microseconds */ 80 SYSCTL_INT(_kern, OID_AUTO, umtx_timeout_max, CTLFLAG_RW, 81 &umtx_timeout_max, 0, ""); 82 83 /* 84 * If the contents of the userland-supplied pointer matches the specified 85 * value enter an interruptable sleep for up to <timeout> microseconds. 86 * If the contents does not match then return immediately. 87 * 88 * Returns 0 if we slept and were woken up, -1 and EWOULDBLOCK if we slept 89 * and timed out, and EBUSY if the contents of the pointer already does 90 * not match the specified value. A timeout of 0 indicates an unlimited sleep. 91 * EINTR is returned if the call was interrupted by a signal (even if 92 * the signal specifies that the system call should restart). 93 * 94 * This function interlocks against call to umtx_wakeup. It does NOT interlock 95 * against changes in *ptr. However, it does not have to. The standard use 96 * of *ptr is to differentiate between an uncontested and a contested mutex 97 * and call umtx_wakeup when releasing a contested mutex. Therefore we can 98 * safely race against changes in *ptr as long as we are properly interlocked 99 * against the umtx_wakeup() call. 100 * 101 * For performance reasons, we do not try to track the underlying page for 102 * mapping changes. Instead, the timeout is capped at kern.umtx_timeout_max 103 * (default 1 second) and the caller is expected to retry. The kernel 104 * will wake all umtx_sleep()s if the process fork()s, but not if it vfork()s. 105 * Other mapping changes must be caught by the timeout. 106 * 107 * umtx_sleep { const int *ptr, int value, int timeout } 108 */ 109 int 110 sys_umtx_sleep(struct sysmsg *sysmsg, const struct umtx_sleep_args *uap) 111 { 112 void *waddr; 113 void *uptr; 114 int offset; 115 int timeout; 116 int error; 117 int value; 118 int fail_counter; 119 thread_t td; 120 volatile const int *ptr = uap->ptr; 121 122 if (uap->timeout < 0) 123 return (EINVAL); 124 td = curthread; 125 126 uptr = __DEQUALIFY(void *, ptr); 127 if ((vm_offset_t)uptr & (sizeof(int) - 1)) 128 return EFAULT; 129 130 offset = (vm_offset_t)uptr & PAGE_MASK; 131 132 /* 133 * Resolve the physical address. We allow the case where there are 134 * sometimes discontinuities (causing a 2 second retry timeout). 135 */ 136 retry_on_discontinuity: 137 fail_counter = 10000; 138 do { 139 if (--fail_counter == 0) { 140 kprintf("umtx_sleep() (X): ERROR Discontinuity %p (%s %d/%d)\n", 141 uptr, td->td_comm, 142 (int)td->td_proc->p_pid, 143 (int)td->td_lwp->lwp_tid); 144 return EINVAL; 145 } 146 value = fuwordadd32(uptr, 0); 147 waddr = (void *)(intptr_t)uservtophys((intptr_t)uptr); 148 } while (waddr == (void *)(intptr_t)-1 && value != -1); 149 150 if (value == -1 && waddr == (void *)(intptr_t)-1) { 151 kprintf("umtx_sleep() (A): WARNING can't translate %p (%s %d/%d)\n", 152 uptr, td->td_comm, 153 (int)td->td_proc->p_pid, 154 (int)td->td_lwp->lwp_tid); 155 return EINVAL; 156 } 157 158 error = EBUSY; 159 if (value == uap->value) { 160 #ifdef _RDTSC_SUPPORTED_ 161 /* 162 * Poll a little while before sleeping, most mutexes are 163 * short-lived. 164 */ 165 if (umtx_delay) { 166 int64_t tsc_target; 167 int good = 0; 168 169 tsc_target = tsc_get_target(umtx_delay); 170 while (tsc_test_target(tsc_target) == 0) { 171 cpu_lfence(); 172 if (fuwordadd32(uptr, 0) != uap->value) { 173 good = 1; 174 break; 175 } 176 cpu_pause(); 177 } 178 if (good) { 179 error = EBUSY; 180 goto done; 181 } 182 } 183 #endif 184 /* 185 * Calculate the timeout. This will be acccurate to within ~2 ticks. 186 * uap->timeout is in microseconds. 187 */ 188 timeout = umtx_timeout_max; 189 if (uap->timeout && uap->timeout < timeout) 190 timeout = uap->timeout; 191 timeout = (timeout / 1000000) * hz + 192 ((timeout % 1000000) * hz + 999999) / 1000000; 193 194 /* 195 * Wake us up if the memory location COWs while we are sleeping. 196 * Use a critical section to tighten up the interlock. Also, 197 * tsleep_remove() requires the caller be in a critical section. 198 */ 199 crit_enter(); 200 201 /* 202 * We must interlock just before sleeping. If we interlock before 203 * registration the lock operations done by the registration can 204 * interfere with it. 205 * 206 * We cannot leave our interlock hanging on return because this 207 * will interfere with umtx_wakeup() calls with limited wakeup 208 * counts. 209 */ 210 tsleep_interlock(waddr, PCATCH | PDOMAIN_UMTX); 211 212 /* 213 * Check physical address changed 214 */ 215 cpu_lfence(); 216 if ((void *)(intptr_t)uservtophys((intptr_t)uptr) != waddr) { 217 crit_exit(); 218 goto retry_on_discontinuity; 219 } 220 221 /* 222 * Re-read value 223 */ 224 value = fuwordadd32(uptr, 0); 225 226 if (value == uap->value) { 227 error = tsleep(waddr, PCATCH | PINTERLOCKED | PDOMAIN_UMTX, 228 "umtxsl", timeout); 229 } else { 230 error = EBUSY; 231 } 232 crit_exit(); 233 /* Always break out in case of signal, even if restartable */ 234 if (error == ERESTART) 235 error = EINTR; 236 } else { 237 error = EBUSY; 238 } 239 done: 240 return(error); 241 } 242 243 /* 244 * umtx_wakeup { const int *ptr, int count } 245 * 246 * Wakeup the specified number of processes held in umtx_sleep() on the 247 * specified user address. A count of 0 wakes up all waiting processes. 248 */ 249 int 250 sys_umtx_wakeup(struct sysmsg *sysmsg, const struct umtx_wakeup_args *uap) 251 { 252 int offset; 253 int error; 254 int fail_counter; 255 int32_t value; 256 void *waddr; 257 void *uptr; 258 volatile const int *ptr = uap->ptr; 259 thread_t td; 260 261 td = curthread; 262 263 /* 264 * WARNING! We can only use vm_fault_page*() for reading data. We 265 * cannot use it for writing data because there is no pmap 266 * interlock to protect against flushes/pageouts. 267 */ 268 cpu_mfence(); 269 if ((vm_offset_t)ptr & (sizeof(int) - 1)) 270 return EFAULT; 271 272 offset = (vm_offset_t)ptr & PAGE_MASK; 273 uptr = __DEQUALIFY(void *, ptr); 274 275 fail_counter = 10000; 276 do { 277 if (--fail_counter == 0) { 278 kprintf("umtx_wakeup() (X): ERROR Discontinuity " 279 "%p (%s %d/%d)\n", 280 uptr, td->td_comm, 281 (int)td->td_proc->p_pid, 282 (int)td->td_lwp->lwp_tid); 283 return EINVAL; 284 } 285 value = fuwordadd32(uptr, 0); 286 waddr = (void *)(intptr_t)uservtophys((intptr_t)uptr); 287 } while (waddr == (void *)(intptr_t)-1 && value != -1); 288 289 if (value == -1 && waddr == (void *)(intptr_t)-1) { 290 kprintf("umtx_wakeup() (A): WARNING can't translate %p (%s %d/%d)\n", 291 uptr, td->td_comm, 292 (int)td->td_proc->p_pid, 293 (int)td->td_lwp->lwp_tid); 294 return EINVAL; 295 } 296 297 if (uap->count == 1) { 298 wakeup_domain_one(waddr, PDOMAIN_UMTX); 299 } else { 300 /* XXX wakes them all up for now */ 301 wakeup_domain(waddr, PDOMAIN_UMTX); 302 } 303 error = 0; 304 305 return(error); 306 } 307