1 /* $NetBSD: kern_lock.c,v 1.173 2021/10/31 16:26:26 skrll Exp $ */ 2 3 /*- 4 * Copyright (c) 2002, 2006, 2007, 2008, 2009, 2020 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility, 9 * NASA Ames Research Center, and by Andrew Doran. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 20 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 21 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 22 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 23 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 24 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 25 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 26 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 27 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 28 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 29 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 30 * POSSIBILITY OF SUCH DAMAGE. 31 */ 32 33 #include <sys/cdefs.h> 34 __KERNEL_RCSID(0, "$NetBSD: kern_lock.c,v 1.173 2021/10/31 16:26:26 skrll Exp $"); 35 36 #ifdef _KERNEL_OPT 37 #include "opt_lockdebug.h" 38 #endif 39 40 #include <sys/param.h> 41 #include <sys/proc.h> 42 #include <sys/lock.h> 43 #include <sys/systm.h> 44 #include <sys/kernel.h> 45 #include <sys/lockdebug.h> 46 #include <sys/cpu.h> 47 #include <sys/syslog.h> 48 #include <sys/atomic.h> 49 #include <sys/lwp.h> 50 #include <sys/pserialize.h> 51 52 #if defined(DIAGNOSTIC) && !defined(LOCKDEBUG) 53 #include <sys/ksyms.h> 54 #endif 55 56 #include <machine/lock.h> 57 58 #include <dev/lockstat.h> 59 60 #define RETURN_ADDRESS (uintptr_t)__builtin_return_address(0) 61 62 bool kernel_lock_dodebug; 63 64 __cpu_simple_lock_t kernel_lock[CACHE_LINE_SIZE / sizeof(__cpu_simple_lock_t)] 65 __cacheline_aligned; 66 67 void 68 assert_sleepable(void) 69 { 70 const char *reason; 71 uint64_t pctr; 72 bool idle; 73 74 if (panicstr != NULL) { 75 return; 76 } 77 78 LOCKDEBUG_BARRIER(kernel_lock, 1); 79 80 /* 81 * Avoid disabling/re-enabling preemption here since this 82 * routine may be called in delicate situations. 83 */ 84 do { 85 pctr = lwp_pctr(); 86 __insn_barrier(); 87 idle = CURCPU_IDLE_P(); 88 __insn_barrier(); 89 } while (pctr != lwp_pctr()); 90 91 reason = NULL; 92 if (idle && !cold) { 93 reason = "idle"; 94 } 95 if (cpu_intr_p()) { 96 reason = "interrupt"; 97 } 98 if (cpu_softintr_p()) { 99 reason = "softint"; 100 } 101 if (!pserialize_not_in_read_section()) { 102 reason = "pserialize"; 103 } 104 105 if (reason) { 106 panic("%s: %s caller=%p", __func__, reason, 107 (void *)RETURN_ADDRESS); 108 } 109 } 110 111 /* 112 * Functions for manipulating the kernel_lock. We put them here 113 * so that they show up in profiles. 114 */ 115 116 #define _KERNEL_LOCK_ABORT(msg) \ 117 LOCKDEBUG_ABORT(__func__, __LINE__, kernel_lock, &_kernel_lock_ops, msg) 118 119 #ifdef LOCKDEBUG 120 #define _KERNEL_LOCK_ASSERT(cond) \ 121 do { \ 122 if (!(cond)) \ 123 _KERNEL_LOCK_ABORT("assertion failed: " #cond); \ 124 } while (/* CONSTCOND */ 0) 125 #else 126 #define _KERNEL_LOCK_ASSERT(cond) /* nothing */ 127 #endif 128 129 static void _kernel_lock_dump(const volatile void *, lockop_printer_t); 130 131 lockops_t _kernel_lock_ops = { 132 .lo_name = "Kernel lock", 133 .lo_type = LOCKOPS_SPIN, 134 .lo_dump = _kernel_lock_dump, 135 }; 136 137 /* 138 * Initialize the kernel lock. 139 */ 140 void 141 kernel_lock_init(void) 142 { 143 144 __cpu_simple_lock_init(kernel_lock); 145 kernel_lock_dodebug = LOCKDEBUG_ALLOC(kernel_lock, &_kernel_lock_ops, 146 RETURN_ADDRESS); 147 } 148 CTASSERT(CACHE_LINE_SIZE >= sizeof(__cpu_simple_lock_t)); 149 150 /* 151 * Print debugging information about the kernel lock. 152 */ 153 static void 154 _kernel_lock_dump(const volatile void *junk, lockop_printer_t pr) 155 { 156 struct cpu_info *ci = curcpu(); 157 158 (void)junk; 159 160 pr("curcpu holds : %18d wanted by: %#018lx\n", 161 ci->ci_biglock_count, (long)ci->ci_biglock_wanted); 162 } 163 164 /* 165 * Acquire 'nlocks' holds on the kernel lock. 166 * 167 * Although it may not look it, this is one of the most central, intricate 168 * routines in the kernel, and tons of code elsewhere depends on its exact 169 * behaviour. If you change something in here, expect it to bite you in the 170 * rear. 171 */ 172 void 173 _kernel_lock(int nlocks) 174 { 175 struct cpu_info *ci; 176 LOCKSTAT_TIMER(spintime); 177 LOCKSTAT_FLAG(lsflag); 178 struct lwp *owant; 179 #ifdef LOCKDEBUG 180 u_int spins = 0; 181 #endif 182 int s; 183 struct lwp *l = curlwp; 184 185 _KERNEL_LOCK_ASSERT(nlocks > 0); 186 187 s = splvm(); 188 ci = curcpu(); 189 if (ci->ci_biglock_count != 0) { 190 _KERNEL_LOCK_ASSERT(__SIMPLELOCK_LOCKED_P(kernel_lock)); 191 ci->ci_biglock_count += nlocks; 192 l->l_blcnt += nlocks; 193 splx(s); 194 return; 195 } 196 197 _KERNEL_LOCK_ASSERT(l->l_blcnt == 0); 198 LOCKDEBUG_WANTLOCK(kernel_lock_dodebug, kernel_lock, RETURN_ADDRESS, 199 0); 200 201 if (__predict_true(__cpu_simple_lock_try(kernel_lock))) { 202 ci->ci_biglock_count = nlocks; 203 l->l_blcnt = nlocks; 204 LOCKDEBUG_LOCKED(kernel_lock_dodebug, kernel_lock, NULL, 205 RETURN_ADDRESS, 0); 206 splx(s); 207 return; 208 } 209 210 /* 211 * To remove the ordering constraint between adaptive mutexes 212 * and kernel_lock we must make it appear as if this thread is 213 * blocking. For non-interlocked mutex release, a store fence 214 * is required to ensure that the result of any mutex_exit() 215 * by the current LWP becomes visible on the bus before the set 216 * of ci->ci_biglock_wanted becomes visible. 217 */ 218 membar_producer(); 219 owant = ci->ci_biglock_wanted; 220 ci->ci_biglock_wanted = l; 221 #if defined(DIAGNOSTIC) && !defined(LOCKDEBUG) 222 l->l_ld_wanted = __builtin_return_address(0); 223 #endif 224 225 /* 226 * Spin until we acquire the lock. Once we have it, record the 227 * time spent with lockstat. 228 */ 229 LOCKSTAT_ENTER(lsflag); 230 LOCKSTAT_START_TIMER(lsflag, spintime); 231 232 do { 233 splx(s); 234 while (__SIMPLELOCK_LOCKED_P(kernel_lock)) { 235 #ifdef LOCKDEBUG 236 if (SPINLOCK_SPINOUT(spins)) { 237 extern int start_init_exec; 238 if (start_init_exec) 239 _KERNEL_LOCK_ABORT("spinout"); 240 } 241 SPINLOCK_BACKOFF_HOOK; 242 SPINLOCK_SPIN_HOOK; 243 #endif 244 } 245 s = splvm(); 246 } while (!__cpu_simple_lock_try(kernel_lock)); 247 248 ci->ci_biglock_count = nlocks; 249 l->l_blcnt = nlocks; 250 LOCKSTAT_STOP_TIMER(lsflag, spintime); 251 LOCKDEBUG_LOCKED(kernel_lock_dodebug, kernel_lock, NULL, 252 RETURN_ADDRESS, 0); 253 if (owant == NULL) { 254 LOCKSTAT_EVENT_RA(lsflag, kernel_lock, 255 LB_KERNEL_LOCK | LB_SPIN, 1, spintime, RETURN_ADDRESS); 256 } 257 LOCKSTAT_EXIT(lsflag); 258 splx(s); 259 260 /* 261 * Now that we have kernel_lock, reset ci_biglock_wanted. This 262 * store must be unbuffered (immediately visible on the bus) in 263 * order for non-interlocked mutex release to work correctly. 264 * It must be visible before a mutex_exit() can execute on this 265 * processor. 266 * 267 * Note: only where CAS is available in hardware will this be 268 * an unbuffered write, but non-interlocked release cannot be 269 * done on CPUs without CAS in hardware. 270 */ 271 (void)atomic_swap_ptr(&ci->ci_biglock_wanted, owant); 272 273 /* 274 * Issue a memory barrier as we have acquired a lock. This also 275 * prevents stores from a following mutex_exit() being reordered 276 * to occur before our store to ci_biglock_wanted above. 277 */ 278 #ifndef __HAVE_ATOMIC_AS_MEMBAR 279 membar_enter(); 280 #endif 281 } 282 283 /* 284 * Release 'nlocks' holds on the kernel lock. If 'nlocks' is zero, release 285 * all holds. 286 */ 287 void 288 _kernel_unlock(int nlocks, int *countp) 289 { 290 struct cpu_info *ci; 291 u_int olocks; 292 int s; 293 struct lwp *l = curlwp; 294 295 _KERNEL_LOCK_ASSERT(nlocks < 2); 296 297 olocks = l->l_blcnt; 298 299 if (olocks == 0) { 300 _KERNEL_LOCK_ASSERT(nlocks <= 0); 301 if (countp != NULL) 302 *countp = 0; 303 return; 304 } 305 306 _KERNEL_LOCK_ASSERT(__SIMPLELOCK_LOCKED_P(kernel_lock)); 307 308 if (nlocks == 0) 309 nlocks = olocks; 310 else if (nlocks == -1) { 311 nlocks = 1; 312 _KERNEL_LOCK_ASSERT(olocks == 1); 313 } 314 s = splvm(); 315 ci = curcpu(); 316 _KERNEL_LOCK_ASSERT(ci->ci_biglock_count >= l->l_blcnt); 317 if (ci->ci_biglock_count == nlocks) { 318 LOCKDEBUG_UNLOCKED(kernel_lock_dodebug, kernel_lock, 319 RETURN_ADDRESS, 0); 320 ci->ci_biglock_count = 0; 321 __cpu_simple_unlock(kernel_lock); 322 l->l_blcnt -= nlocks; 323 splx(s); 324 if (l->l_dopreempt) 325 kpreempt(0); 326 } else { 327 ci->ci_biglock_count -= nlocks; 328 l->l_blcnt -= nlocks; 329 splx(s); 330 } 331 332 if (countp != NULL) 333 *countp = olocks; 334 } 335 336 bool 337 _kernel_locked_p(void) 338 { 339 return __SIMPLELOCK_LOCKED_P(kernel_lock); 340 } 341