kern_lock.c revision 1.174
1 /* $NetBSD: kern_lock.c,v 1.174 2022/08/16 00:26:39 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 1.174 2022/08/16 00:26:39 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 ci->ci_biglock_count = nlocks; 220 l->l_blcnt = nlocks; 221 LOCKDEBUG_LOCKED(kernel_lock_dodebug, kernel_lock, NULL, 222 RETURN_ADDRESS, 0); 223 splx(s); 224 return; 225 } 226 227 /* 228 * To remove the ordering constraint between adaptive mutexes 229 * and kernel_lock we must make it appear as if this thread is 230 * blocking. For non-interlocked mutex release, a store fence 231 * is required to ensure that the result of any mutex_exit() 232 * by the current LWP becomes visible on the bus before the set 233 * of ci->ci_biglock_wanted becomes visible. 234 */ 235 membar_producer(); 236 owant = ci->ci_biglock_wanted; 237 ci->ci_biglock_wanted = l; 238 #if defined(DIAGNOSTIC) && !defined(LOCKDEBUG) 239 l->l_ld_wanted = __builtin_return_address(0); 240 #endif 241 242 /* 243 * Spin until we acquire the lock. Once we have it, record the 244 * time spent with lockstat. 245 */ 246 LOCKSTAT_ENTER(lsflag); 247 LOCKSTAT_START_TIMER(lsflag, spintime); 248 249 do { 250 splx(s); 251 while (__SIMPLELOCK_LOCKED_P(kernel_lock)) { 252 #ifdef LOCKDEBUG 253 if (SPINLOCK_SPINOUT(spins)) { 254 extern int start_init_exec; 255 ipi_msg_t msg = { 256 .func = kernel_lock_trace_ipi, 257 }; 258 ipi_unicast(&msg, kernel_lock_holder); 259 ipi_wait(&msg); 260 if (start_init_exec) 261 _KERNEL_LOCK_ABORT("spinout"); 262 } 263 SPINLOCK_BACKOFF_HOOK; 264 SPINLOCK_SPIN_HOOK; 265 #endif 266 } 267 s = splvm(); 268 } while (!__cpu_simple_lock_try(kernel_lock)); 269 270 ci->ci_biglock_count = nlocks; 271 l->l_blcnt = nlocks; 272 LOCKSTAT_STOP_TIMER(lsflag, spintime); 273 LOCKDEBUG_LOCKED(kernel_lock_dodebug, kernel_lock, NULL, 274 RETURN_ADDRESS, 0); 275 if (owant == NULL) { 276 LOCKSTAT_EVENT_RA(lsflag, kernel_lock, 277 LB_KERNEL_LOCK | LB_SPIN, 1, spintime, RETURN_ADDRESS); 278 } 279 LOCKSTAT_EXIT(lsflag); 280 splx(s); 281 282 /* 283 * Now that we have kernel_lock, reset ci_biglock_wanted. This 284 * store must be unbuffered (immediately visible on the bus) in 285 * order for non-interlocked mutex release to work correctly. 286 * It must be visible before a mutex_exit() can execute on this 287 * processor. 288 * 289 * Note: only where CAS is available in hardware will this be 290 * an unbuffered write, but non-interlocked release cannot be 291 * done on CPUs without CAS in hardware. 292 */ 293 (void)atomic_swap_ptr(&ci->ci_biglock_wanted, owant); 294 295 /* 296 * Issue a memory barrier as we have acquired a lock. This also 297 * prevents stores from a following mutex_exit() being reordered 298 * to occur before our store to ci_biglock_wanted above. 299 */ 300 #ifndef __HAVE_ATOMIC_AS_MEMBAR 301 membar_enter(); 302 #endif 303 304 #ifdef LOCKDEBUG 305 kernel_lock_holder = curcpu(); 306 #endif 307 } 308 309 /* 310 * Release 'nlocks' holds on the kernel lock. If 'nlocks' is zero, release 311 * all holds. 312 */ 313 void 314 _kernel_unlock(int nlocks, int *countp) 315 { 316 struct cpu_info *ci; 317 u_int olocks; 318 int s; 319 struct lwp *l = curlwp; 320 321 _KERNEL_LOCK_ASSERT(nlocks < 2); 322 323 olocks = l->l_blcnt; 324 325 if (olocks == 0) { 326 _KERNEL_LOCK_ASSERT(nlocks <= 0); 327 if (countp != NULL) 328 *countp = 0; 329 return; 330 } 331 332 _KERNEL_LOCK_ASSERT(__SIMPLELOCK_LOCKED_P(kernel_lock)); 333 334 if (nlocks == 0) 335 nlocks = olocks; 336 else if (nlocks == -1) { 337 nlocks = 1; 338 _KERNEL_LOCK_ASSERT(olocks == 1); 339 } 340 s = splvm(); 341 ci = curcpu(); 342 _KERNEL_LOCK_ASSERT(ci->ci_biglock_count >= l->l_blcnt); 343 if (ci->ci_biglock_count == nlocks) { 344 LOCKDEBUG_UNLOCKED(kernel_lock_dodebug, kernel_lock, 345 RETURN_ADDRESS, 0); 346 ci->ci_biglock_count = 0; 347 __cpu_simple_unlock(kernel_lock); 348 l->l_blcnt -= nlocks; 349 splx(s); 350 if (l->l_dopreempt) 351 kpreempt(0); 352 } else { 353 ci->ci_biglock_count -= nlocks; 354 l->l_blcnt -= nlocks; 355 splx(s); 356 } 357 358 if (countp != NULL) 359 *countp = olocks; 360 } 361 362 bool 363 _kernel_locked_p(void) 364 { 365 return __SIMPLELOCK_LOCKED_P(kernel_lock); 366 } 367
Indexes created Mon Sep 22 13:09:51 GMT 2025