sx.h revision 192853
1/*- 2 * Copyright (c) 2007 Attilio Rao <attilio@freebsd.org> 3 * Copyright (c) 2001 Jason Evans <jasone@freebsd.org> 4 * All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice(s), this list of conditions and the following disclaimer as 11 * the first lines of this file unmodified other than the possible 12 * addition of one or more copyright notices. 13 * 2. Redistributions in binary form must reproduce the above copyright 14 * notice(s), this list of conditions and the following disclaimer in the 15 * documentation and/or other materials provided with the distribution. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY 18 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 19 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 20 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY 21 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 22 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 23 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 24 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH 27 * DAMAGE. 28 * 29 * $FreeBSD: head/sys/sys/sx.h 192853 2009-05-26 20:28:22Z sson $ 30 */ 31 32#ifndef _SYS_SX_H_ 33#define _SYS_SX_H_ 34 35#include <sys/_lock.h> 36#include <sys/_sx.h> 37 38#ifdef _KERNEL 39#include <sys/pcpu.h> 40#include <sys/lock_profile.h> 41#include <sys/lockstat.h> 42#include <machine/atomic.h> 43#endif 44 45/* 46 * In general, the sx locks and rwlocks use very similar algorithms. 47 * The main difference in the implementations is how threads are 48 * blocked when a lock is unavailable. For this, sx locks use sleep 49 * queues which do not support priority propagation, and rwlocks use 50 * turnstiles which do. 51 * 52 * The sx_lock field consists of several fields. The low bit 53 * indicates if the lock is locked with a shared or exclusive lock. A 54 * value of 0 indicates an exclusive lock, and a value of 1 indicates 55 * a shared lock. Bit 1 is a boolean indicating if there are any 56 * threads waiting for a shared lock. Bit 2 is a boolean indicating 57 * if there are any threads waiting for an exclusive lock. Bit 3 is a 58 * boolean indicating if an exclusive lock is recursively held. The 59 * rest of the variable's definition is dependent on the value of the 60 * first bit. For an exclusive lock, it is a pointer to the thread 61 * holding the lock, similar to the mtx_lock field of mutexes. For 62 * shared locks, it is a count of read locks that are held. 63 * 64 * When the lock is not locked by any thread, it is encoded as a 65 * shared lock with zero waiters. 66 * 67 * A note about memory barriers. Exclusive locks need to use the same 68 * memory barriers as mutexes: _acq when acquiring an exclusive lock 69 * and _rel when releasing an exclusive lock. On the other side, 70 * shared lock needs to use an _acq barrier when acquiring the lock 71 * but, since they don't update any locked data, no memory barrier is 72 * needed when releasing a shared lock. 73 */ 74 75#define SX_LOCK_SHARED 0x01 76#define SX_LOCK_SHARED_WAITERS 0x02 77#define SX_LOCK_EXCLUSIVE_WAITERS 0x04 78#define SX_LOCK_RECURSED 0x08 79#define SX_LOCK_FLAGMASK \ 80 (SX_LOCK_SHARED | SX_LOCK_SHARED_WAITERS | \ 81 SX_LOCK_EXCLUSIVE_WAITERS | SX_LOCK_RECURSED) 82 83#define SX_OWNER(x) ((x) & ~SX_LOCK_FLAGMASK) 84#define SX_SHARERS_SHIFT 4 85#define SX_SHARERS(x) (SX_OWNER(x) >> SX_SHARERS_SHIFT) 86#define SX_SHARERS_LOCK(x) \ 87 ((x) << SX_SHARERS_SHIFT | SX_LOCK_SHARED) 88#define SX_ONE_SHARER (1 << SX_SHARERS_SHIFT) 89 90#define SX_LOCK_UNLOCKED SX_SHARERS_LOCK(0) 91#define SX_LOCK_DESTROYED \ 92 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS) 93 94#ifdef _KERNEL 95 96/* 97 * Function prototipes. Routines that start with an underscore are not part 98 * of the public interface and are wrappered with a macro. 99 */ 100void sx_sysinit(void *arg); 101#define sx_init(sx, desc) sx_init_flags((sx), (desc), 0) 102void sx_init_flags(struct sx *sx, const char *description, int opts); 103void sx_destroy(struct sx *sx); 104int _sx_slock(struct sx *sx, int opts, const char *file, int line); 105int _sx_xlock(struct sx *sx, int opts, const char *file, int line); 106int _sx_try_slock(struct sx *sx, const char *file, int line); 107int _sx_try_xlock(struct sx *sx, const char *file, int line); 108void _sx_sunlock(struct sx *sx, const char *file, int line); 109void _sx_xunlock(struct sx *sx, const char *file, int line); 110int _sx_try_upgrade(struct sx *sx, const char *file, int line); 111void _sx_downgrade(struct sx *sx, const char *file, int line); 112int _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, 113 const char *file, int line); 114int _sx_slock_hard(struct sx *sx, int opts, const char *file, int line); 115void _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int 116 line); 117void _sx_sunlock_hard(struct sx *sx, const char *file, int line); 118#if defined(INVARIANTS) || defined(INVARIANT_SUPPORT) 119void _sx_assert(struct sx *sx, int what, const char *file, int line); 120#endif 121#ifdef DDB 122int sx_chain(struct thread *td, struct thread **ownerp); 123#endif 124 125struct sx_args { 126 struct sx *sa_sx; 127 const char *sa_desc; 128}; 129 130#define SX_SYSINIT(name, sxa, desc) \ 131 static struct sx_args name##_args = { \ 132 (sxa), \ 133 (desc) \ 134 }; \ 135 SYSINIT(name##_sx_sysinit, SI_SUB_LOCK, SI_ORDER_MIDDLE, \ 136 sx_sysinit, &name##_args); \ 137 SYSUNINIT(name##_sx_sysuninit, SI_SUB_LOCK, SI_ORDER_MIDDLE, \ 138 sx_destroy, (sxa)) 139 140/* 141 * Full lock operations that are suitable to be inlined in non-debug kernels. 142 * If the lock can't be acquired or released trivially then the work is 143 * deferred to 'tougher' functions. 144 */ 145 146/* Acquire an exclusive lock. */ 147static __inline int 148__sx_xlock(struct sx *sx, struct thread *td, int opts, const char *file, 149 int line) 150{ 151 uintptr_t tid = (uintptr_t)td; 152 int error = 0; 153 154 if (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) 155 error = _sx_xlock_hard(sx, tid, opts, file, line); 156 else 157 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, 158 sx, 0, 0, file, line); 159 160 return (error); 161} 162 163/* Release an exclusive lock. */ 164static __inline void 165__sx_xunlock(struct sx *sx, struct thread *td, const char *file, int line) 166{ 167 uintptr_t tid = (uintptr_t)td; 168 169 if (!atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED)) 170 _sx_xunlock_hard(sx, tid, file, line); 171} 172 173/* Acquire a shared lock. */ 174static __inline int 175__sx_slock(struct sx *sx, int opts, const char *file, int line) 176{ 177 uintptr_t x = sx->sx_lock; 178 int error = 0; 179 180 if (!(x & SX_LOCK_SHARED) || 181 !atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) 182 error = _sx_slock_hard(sx, opts, file, line); 183 else 184 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx, 0, 185 0, file, line); 186 187 return (error); 188} 189 190/* 191 * Release a shared lock. We can just drop a single shared lock so 192 * long as we aren't trying to drop the last shared lock when other 193 * threads are waiting for an exclusive lock. This takes advantage of 194 * the fact that an unlocked lock is encoded as a shared lock with a 195 * count of 0. 196 */ 197static __inline void 198__sx_sunlock(struct sx *sx, const char *file, int line) 199{ 200 uintptr_t x = sx->sx_lock; 201 202 if (x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS) || 203 !atomic_cmpset_ptr(&sx->sx_lock, x, x - SX_ONE_SHARER)) 204 _sx_sunlock_hard(sx, file, line); 205} 206 207/* 208 * Public interface for lock operations. 209 */ 210#ifndef LOCK_DEBUG 211#error "LOCK_DEBUG not defined, include <sys/lock.h> before <sys/sx.h>" 212#endif 213#if (LOCK_DEBUG > 0) || defined(SX_NOINLINE) 214#define sx_xlock(sx) (void)_sx_xlock((sx), 0, LOCK_FILE, LOCK_LINE) 215#define sx_xlock_sig(sx) \ 216 _sx_xlock((sx), SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE) 217#define sx_xunlock(sx) _sx_xunlock((sx), LOCK_FILE, LOCK_LINE) 218#define sx_slock(sx) (void)_sx_slock((sx), 0, LOCK_FILE, LOCK_LINE) 219#define sx_slock_sig(sx) \ 220 _sx_slock((sx), SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE) 221#define sx_sunlock(sx) _sx_sunlock((sx), LOCK_FILE, LOCK_LINE) 222#else 223#define sx_xlock(sx) \ 224 (void)__sx_xlock((sx), curthread, 0, LOCK_FILE, LOCK_LINE) 225#define sx_xlock_sig(sx) \ 226 __sx_xlock((sx), curthread, SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE) 227#define sx_xunlock(sx) \ 228 __sx_xunlock((sx), curthread, LOCK_FILE, LOCK_LINE) 229#define sx_slock(sx) (void)__sx_slock((sx), 0, LOCK_FILE, LOCK_LINE) 230#define sx_slock_sig(sx) \ 231 __sx_slock((sx), SX_INTERRUPTIBLE, LOCK_FILE, LOCK_LINE) 232#define sx_sunlock(sx) __sx_sunlock((sx), LOCK_FILE, LOCK_LINE) 233#endif /* LOCK_DEBUG > 0 || SX_NOINLINE */ 234#define sx_try_slock(sx) _sx_try_slock((sx), LOCK_FILE, LOCK_LINE) 235#define sx_try_xlock(sx) _sx_try_xlock((sx), LOCK_FILE, LOCK_LINE) 236#define sx_try_upgrade(sx) _sx_try_upgrade((sx), LOCK_FILE, LOCK_LINE) 237#define sx_downgrade(sx) _sx_downgrade((sx), LOCK_FILE, LOCK_LINE) 238 239/* 240 * Return a pointer to the owning thread if the lock is exclusively 241 * locked. 242 */ 243#define sx_xholder(sx) \ 244 ((sx)->sx_lock & SX_LOCK_SHARED ? NULL : \ 245 (struct thread *)SX_OWNER((sx)->sx_lock)) 246 247#define sx_xlocked(sx) \ 248 (((sx)->sx_lock & ~(SX_LOCK_FLAGMASK & ~SX_LOCK_SHARED)) == \ 249 (uintptr_t)curthread) 250 251#define sx_unlock(sx) do { \ 252 if (sx_xlocked(sx)) \ 253 sx_xunlock(sx); \ 254 else \ 255 sx_sunlock(sx); \ 256} while (0) 257 258#define sx_sleep(chan, sx, pri, wmesg, timo) \ 259 _sleep((chan), &(sx)->lock_object, (pri), (wmesg), (timo)) 260 261/* 262 * Options passed to sx_init_flags(). 263 */ 264#define SX_DUPOK 0x01 265#define SX_NOPROFILE 0x02 266#define SX_NOWITNESS 0x04 267#define SX_QUIET 0x08 268#define SX_ADAPTIVESPIN 0x10 269#define SX_RECURSE 0x20 270 271/* 272 * Options passed to sx_*lock_hard(). 273 */ 274#define SX_INTERRUPTIBLE 0x40 275 276#if defined(INVARIANTS) || defined(INVARIANT_SUPPORT) 277#define SA_LOCKED LA_LOCKED 278#define SA_SLOCKED LA_SLOCKED 279#define SA_XLOCKED LA_XLOCKED 280#define SA_UNLOCKED LA_UNLOCKED 281#define SA_RECURSED LA_RECURSED 282#define SA_NOTRECURSED LA_NOTRECURSED 283 284/* Backwards compatability. */ 285#define SX_LOCKED LA_LOCKED 286#define SX_SLOCKED LA_SLOCKED 287#define SX_XLOCKED LA_XLOCKED 288#define SX_UNLOCKED LA_UNLOCKED 289#define SX_RECURSED LA_RECURSED 290#define SX_NOTRECURSED LA_NOTRECURSED 291#endif 292 293#ifdef INVARIANTS 294#define sx_assert(sx, what) _sx_assert((sx), (what), LOCK_FILE, LOCK_LINE) 295#else 296#define sx_assert(sx, what) 297#endif 298 299#endif /* _KERNEL */ 300 301#endif /* !_SYS_SX_H_ */ 302