kern_lock.c revision 1.178
1 /* $NetBSD: kern_lock.c,v 1.178 2022/08/20 23:37:12 riastradh 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 1.178 2022/08/20 23:37:12 riastradh 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 #ifdef LOCKDEBUG 138 139 #include <ddb/ddb.h> 140 141 static void 142 kernel_lock_trace_ipi(void *cookie) 143 { 144 145 printf("%s[%d %s]: hogging kernel lock\n", cpu_name(curcpu()), 146 curlwp->l_lid, 147 curlwp->l_name ? curlwp->l_name : curproc->p_comm); 148 db_stacktrace(); 149 } 150 151 #endif 152 153 /* 154 * Initialize the kernel lock. 155 */ 156 void 157 kernel_lock_init(void) 158 { 159 160 __cpu_simple_lock_init(kernel_lock); 161 kernel_lock_dodebug = LOCKDEBUG_ALLOC(kernel_lock, &_kernel_lock_ops, 162 RETURN_ADDRESS); 163 } 164 CTASSERT(CACHE_LINE_SIZE >= sizeof(__cpu_simple_lock_t)); 165 166 /* 167 * Print debugging information about the kernel lock. 168 */ 169 static void 170 _kernel_lock_dump(const volatile void *junk, lockop_printer_t pr) 171 { 172 struct cpu_info *ci = curcpu(); 173 174 (void)junk; 175 176 pr("curcpu holds : %18d wanted by: %#018lx\n", 177 ci->ci_biglock_count, (long)ci->ci_biglock_wanted); 178 } 179 180 /* 181 * Acquire 'nlocks' holds on the kernel lock. 182 * 183 * Although it may not look it, this is one of the most central, intricate 184 * routines in the kernel, and tons of code elsewhere depends on its exact 185 * behaviour. If you change something in here, expect it to bite you in the 186 * rear. 187 */ 188 void 189 _kernel_lock(int nlocks) 190 { 191 struct cpu_info *ci; 192 LOCKSTAT_TIMER(spintime); 193 LOCKSTAT_FLAG(lsflag); 194 struct lwp *owant; 195 #ifdef LOCKDEBUG 196 static struct cpu_info *kernel_lock_holder; 197 u_int spins = 0; 198 #endif 199 int s; 200 struct lwp *l = curlwp; 201 202 _KERNEL_LOCK_ASSERT(nlocks > 0); 203 204 s = splvm(); 205 ci = curcpu(); 206 if (ci->ci_biglock_count != 0) { 207 _KERNEL_LOCK_ASSERT(__SIMPLELOCK_LOCKED_P(kernel_lock)); 208 ci->ci_biglock_count += nlocks; 209 l->l_blcnt += nlocks; 210 splx(s); 211 return; 212 } 213 214 _KERNEL_LOCK_ASSERT(l->l_blcnt == 0); 215 LOCKDEBUG_WANTLOCK(kernel_lock_dodebug, kernel_lock, RETURN_ADDRESS, 216 0); 217 218 if (__predict_true(__cpu_simple_lock_try(kernel_lock))) { 219 #ifdef LOCKDEBUG 220 kernel_lock_holder = curcpu(); 221 #endif 222 ci->ci_biglock_count = nlocks; 223 l->l_blcnt = nlocks; 224 LOCKDEBUG_LOCKED(kernel_lock_dodebug, kernel_lock, NULL, 225 RETURN_ADDRESS, 0); 226 splx(s); 227 return; 228 } 229 230 /* 231 * To remove the ordering constraint between adaptive mutexes 232 * and kernel_lock we must make it appear as if this thread is 233 * blocking. For non-interlocked mutex release, a store fence 234 * is required to ensure that the result of any mutex_exit() 235 * by the current LWP becomes visible on the bus before the set 236 * of ci->ci_biglock_wanted becomes visible. 237 */ 238 membar_producer(); 239 owant = ci->ci_biglock_wanted; 240 ci->ci_biglock_wanted = l; 241 #if defined(DIAGNOSTIC) && !defined(LOCKDEBUG) 242 l->l_ld_wanted = __builtin_return_address(0); 243 #endif 244 245 /* 246 * Spin until we acquire the lock. Once we have it, record the 247 * time spent with lockstat. 248 */ 249 LOCKSTAT_ENTER(lsflag); 250 LOCKSTAT_START_TIMER(lsflag, spintime); 251 252 do { 253 splx(s); 254 while (__SIMPLELOCK_LOCKED_P(kernel_lock)) { 255 #ifdef LOCKDEBUG 256 extern int start_init_exec; 257 if (SPINLOCK_SPINOUT(spins) && start_init_exec) { 258 ipi_msg_t msg = { 259 .func = kernel_lock_trace_ipi, 260 }; 261 kpreempt_disable(); 262 ipi_unicast(&msg, kernel_lock_holder); 263 ipi_wait(&msg); 264 kpreempt_enable(); 265 _KERNEL_LOCK_ABORT("spinout"); 266 } 267 SPINLOCK_BACKOFF_HOOK; 268 SPINLOCK_SPIN_HOOK; 269 #endif 270 } 271 s = splvm(); 272 } while (!__cpu_simple_lock_try(kernel_lock)); 273 274 ci->ci_biglock_count = nlocks; 275 l->l_blcnt = nlocks; 276 LOCKSTAT_STOP_TIMER(lsflag, spintime); 277 LOCKDEBUG_LOCKED(kernel_lock_dodebug, kernel_lock, NULL, 278 RETURN_ADDRESS, 0); 279 if (owant == NULL) { 280 LOCKSTAT_EVENT_RA(lsflag, kernel_lock, 281 LB_KERNEL_LOCK | LB_SPIN, 1, spintime, RETURN_ADDRESS); 282 } 283 LOCKSTAT_EXIT(lsflag); 284 splx(s); 285 286 /* 287 * Now that we have kernel_lock, reset ci_biglock_wanted. This 288 * store must be unbuffered (immediately visible on the bus) in 289 * order for non-interlocked mutex release to work correctly. 290 * It must be visible before a mutex_exit() can execute on this 291 * processor. 292 * 293 * Note: only where CAS is available in hardware will this be 294 * an unbuffered write, but non-interlocked release cannot be 295 * done on CPUs without CAS in hardware. 296 */ 297 (void)atomic_swap_ptr(&ci->ci_biglock_wanted, owant); 298 299 /* 300 * Issue a memory barrier as we have acquired a lock. This also 301 * prevents stores from a following mutex_exit() being reordered 302 * to occur before our store to ci_biglock_wanted above. 303 */ 304 #ifndef __HAVE_ATOMIC_AS_MEMBAR 305 membar_enter(); 306 #endif 307 308 #ifdef LOCKDEBUG 309 kernel_lock_holder = curcpu(); 310 #endif 311 } 312 313 /* 314 * Release 'nlocks' holds on the kernel lock. If 'nlocks' is zero, release 315 * all holds. 316 */ 317 void 318 _kernel_unlock(int nlocks, int *countp) 319 { 320 struct cpu_info *ci; 321 u_int olocks; 322 int s; 323 struct lwp *l = curlwp; 324 325 _KERNEL_LOCK_ASSERT(nlocks < 2); 326 327 olocks = l->l_blcnt; 328 329 if (olocks == 0) { 330 _KERNEL_LOCK_ASSERT(nlocks <= 0); 331 if (countp != NULL) 332 *countp = 0; 333 return; 334 } 335 336 _KERNEL_LOCK_ASSERT(__SIMPLELOCK_LOCKED_P(kernel_lock)); 337 338 if (nlocks == 0) 339 nlocks = olocks; 340 else if (nlocks == -1) { 341 nlocks = 1; 342 _KERNEL_LOCK_ASSERT(olocks == 1); 343 } 344 s = splvm(); 345 ci = curcpu(); 346 _KERNEL_LOCK_ASSERT(ci->ci_biglock_count >= l->l_blcnt); 347 if (ci->ci_biglock_count == nlocks) { 348 LOCKDEBUG_UNLOCKED(kernel_lock_dodebug, kernel_lock, 349 RETURN_ADDRESS, 0); 350 ci->ci_biglock_count = 0; 351 __cpu_simple_unlock(kernel_lock); 352 l->l_blcnt -= nlocks; 353 splx(s); 354 if (l->l_dopreempt) 355 kpreempt(0); 356 } else { 357 ci->ci_biglock_count -= nlocks; 358 l->l_blcnt -= nlocks; 359 splx(s); 360 } 361 362 if (countp != NULL) 363 *countp = olocks; 364 } 365 366 bool 367 _kernel_locked_p(void) 368 { 369 return __SIMPLELOCK_LOCKED_P(kernel_lock); 370 } 371
Indexes created Mon Sep 22 10:09:38 GMT 2025