The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/sys/sx.h

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    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: releng/9.1/sys/sys/sx.h 230799 2012-01-31 01:45:20Z attilio $
   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 
   68 #define SX_LOCK_SHARED                  0x01
   69 #define SX_LOCK_SHARED_WAITERS          0x02
   70 #define SX_LOCK_EXCLUSIVE_WAITERS       0x04
   71 #define SX_LOCK_RECURSED                0x08
   72 #define SX_LOCK_FLAGMASK                                                \
   73         (SX_LOCK_SHARED | SX_LOCK_SHARED_WAITERS |                      \
   74         SX_LOCK_EXCLUSIVE_WAITERS | SX_LOCK_RECURSED)
   75 
   76 #define SX_OWNER(x)                     ((x) & ~SX_LOCK_FLAGMASK)
   77 #define SX_SHARERS_SHIFT                4
   78 #define SX_SHARERS(x)                   (SX_OWNER(x) >> SX_SHARERS_SHIFT)
   79 #define SX_SHARERS_LOCK(x)                                              \
   80         ((x) << SX_SHARERS_SHIFT | SX_LOCK_SHARED)
   81 #define SX_ONE_SHARER                   (1 << SX_SHARERS_SHIFT)
   82 
   83 #define SX_LOCK_UNLOCKED                SX_SHARERS_LOCK(0)
   84 #define SX_LOCK_DESTROYED                                               \
   85         (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)
   86 
   87 #ifdef _KERNEL
   88 
   89 /*
   90  * Function prototipes.  Routines that start with an underscore are not part
   91  * of the public interface and are wrappered with a macro.
   92  */
   93 void    sx_sysinit(void *arg);
   94 #define sx_init(sx, desc)       sx_init_flags((sx), (desc), 0)
   95 void    sx_init_flags(struct sx *sx, const char *description, int opts);
   96 void    sx_destroy(struct sx *sx);
   97 int     _sx_slock(struct sx *sx, int opts, const char *file, int line);
   98 int     _sx_xlock(struct sx *sx, int opts, const char *file, int line);
   99 int     _sx_try_slock(struct sx *sx, const char *file, int line);
  100 int     _sx_try_xlock(struct sx *sx, const char *file, int line);
  101 void    _sx_sunlock(struct sx *sx, const char *file, int line);
  102 void    _sx_xunlock(struct sx *sx, const char *file, int line);
  103 int     _sx_try_upgrade(struct sx *sx, const char *file, int line);
  104 void    _sx_downgrade(struct sx *sx, const char *file, int line);
  105 int     _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts,
  106             const char *file, int line);
  107 int     _sx_slock_hard(struct sx *sx, int opts, const char *file, int line);
  108 void    _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int
  109             line);
  110 void    _sx_sunlock_hard(struct sx *sx, const char *file, int line);
  111 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
  112 void    _sx_assert(struct sx *sx, int what, const char *file, int line);
  113 #endif
  114 #ifdef DDB
  115 int     sx_chain(struct thread *td, struct thread **ownerp);
  116 #endif
  117 
  118 #define sx_downgrade_(sx, file, line)                                   \
  119         _sx_downgrade((sx), (file), (line))
  120 #define sx_try_slock_(sx, file, line)                                   \
  121         _sx_try_slock((sx), (file), (line))
  122 #define sx_try_xlock_(sx, file, line)                                   \
  123         _sx_try_xlock((sx), (file), (line))
  124 #define sx_try_upgrade_(sx, file, line)                                 \
  125         _sx_try_upgrade((sx), (file), (line))
  126 
  127 struct sx_args {
  128         struct sx       *sa_sx;
  129         const char      *sa_desc;
  130         int             sa_flags;
  131 };
  132 
  133 #define SX_SYSINIT_FLAGS(name, sxa, desc, flags)                        \
  134         static struct sx_args name##_args = {                           \
  135                 (sxa),                                                  \
  136                 (desc),                                                 \
  137                 (flags)                                                 \
  138         };                                                              \
  139         SYSINIT(name##_sx_sysinit, SI_SUB_LOCK, SI_ORDER_MIDDLE,        \
  140             sx_sysinit, &name##_args);                                  \
  141         SYSUNINIT(name##_sx_sysuninit, SI_SUB_LOCK, SI_ORDER_MIDDLE,    \
  142             sx_destroy, (sxa))
  143 
  144 #define SX_SYSINIT(name, sxa, desc)     SX_SYSINIT_FLAGS(name, sxa, desc, 0)
  145 
  146 /*
  147  * Full lock operations that are suitable to be inlined in non-debug kernels.
  148  * If the lock can't be acquired or released trivially then the work is
  149  * deferred to 'tougher' functions.
  150  */
  151 
  152 /* Acquire an exclusive lock. */
  153 static __inline int
  154 __sx_xlock(struct sx *sx, struct thread *td, int opts, const char *file,
  155     int line)
  156 {
  157         uintptr_t tid = (uintptr_t)td;
  158         int error = 0;
  159 
  160         if (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid))
  161                 error = _sx_xlock_hard(sx, tid, opts, file, line);
  162         else 
  163                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE,
  164                     sx, 0, 0, file, line);
  165 
  166         return (error);
  167 }
  168 
  169 /* Release an exclusive lock. */
  170 static __inline void
  171 __sx_xunlock(struct sx *sx, struct thread *td, const char *file, int line)
  172 {
  173         uintptr_t tid = (uintptr_t)td;
  174 
  175         if (!atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
  176                 _sx_xunlock_hard(sx, tid, file, line);
  177 }
  178 
  179 /* Acquire a shared lock. */
  180 static __inline int
  181 __sx_slock(struct sx *sx, int opts, const char *file, int line)
  182 {
  183         uintptr_t x = sx->sx_lock;
  184         int error = 0;
  185 
  186         if (!(x & SX_LOCK_SHARED) ||
  187             !atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER))
  188                 error = _sx_slock_hard(sx, opts, file, line);
  189         else
  190                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx, 0,
  191                     0, file, line);
  192 
  193         return (error);
  194 }
  195 
  196 /*
  197  * Release a shared lock.  We can just drop a single shared lock so
  198  * long as we aren't trying to drop the last shared lock when other
  199  * threads are waiting for an exclusive lock.  This takes advantage of
  200  * the fact that an unlocked lock is encoded as a shared lock with a
  201  * count of 0.
  202  */
  203 static __inline void
  204 __sx_sunlock(struct sx *sx, const char *file, int line)
  205 {
  206         uintptr_t x = sx->sx_lock;
  207 
  208         if (x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS) ||
  209             !atomic_cmpset_rel_ptr(&sx->sx_lock, x, x - SX_ONE_SHARER))
  210                 _sx_sunlock_hard(sx, file, line);
  211 }
  212 
  213 /*
  214  * Public interface for lock operations.
  215  */
  216 #ifndef LOCK_DEBUG
  217 #error  "LOCK_DEBUG not defined, include <sys/lock.h> before <sys/sx.h>"
  218 #endif
  219 #if     (LOCK_DEBUG > 0) || defined(SX_NOINLINE)
  220 #define sx_xlock_(sx, file, line)                                       \
  221         (void)_sx_xlock((sx), 0, (file), (line))
  222 #define sx_xlock_sig_(sx, file, line)                                   \
  223         _sx_xlock((sx), SX_INTERRUPTIBLE, (file), (line))
  224 #define sx_xunlock_(sx, file, line)                                     \
  225         _sx_xunlock((sx), (file), (line))
  226 #define sx_slock_(sx, file, line)                                       \
  227         (void)_sx_slock((sx), 0, (file), (line))
  228 #define sx_slock_sig_(sx, file, line)                                   \
  229         _sx_slock((sx), SX_INTERRUPTIBLE, (file) , (line))
  230 #define sx_sunlock_(sx, file, line)                                     \
  231         _sx_sunlock((sx), (file), (line))
  232 #else
  233 #define sx_xlock_(sx, file, line)                                       \
  234         (void)__sx_xlock((sx), curthread, 0, (file), (line))
  235 #define sx_xlock_sig_(sx, file, line)                                   \
  236         __sx_xlock((sx), curthread, SX_INTERRUPTIBLE, (file), (line))
  237 #define sx_xunlock_(sx, file, line)                                     \
  238         __sx_xunlock((sx), curthread, (file), (line))
  239 #define sx_slock_(sx, file, line)                                       \
  240         (void)__sx_slock((sx), 0, (file), (line))
  241 #define sx_slock_sig_(sx, file, line)                                   \
  242         __sx_slock((sx), SX_INTERRUPTIBLE, (file), (line))
  243 #define sx_sunlock_(sx, file, line)                                     \
  244         __sx_sunlock((sx), (file), (line))
  245 #endif  /* LOCK_DEBUG > 0 || SX_NOINLINE */
  246 #define sx_try_slock(sx)        sx_try_slock_((sx), LOCK_FILE, LOCK_LINE)
  247 #define sx_try_xlock(sx)        sx_try_xlock_((sx), LOCK_FILE, LOCK_LINE)
  248 #define sx_try_upgrade(sx)      sx_try_upgrade_((sx), LOCK_FILE, LOCK_LINE)
  249 #define sx_downgrade(sx)        sx_downgrade_((sx), LOCK_FILE, LOCK_LINE)
  250 #ifdef INVARIANTS
  251 #define sx_assert_(sx, what, file, line)                                \
  252         _sx_assert((sx), (what), (file), (line))
  253 #else
  254 #define sx_assert_(sx, what, file, line)        (void)0
  255 #endif
  256 
  257 #define sx_xlock(sx)            sx_xlock_((sx), LOCK_FILE, LOCK_LINE)
  258 #define sx_xlock_sig(sx)        sx_xlock_sig_((sx), LOCK_FILE, LOCK_LINE)
  259 #define sx_xunlock(sx)          sx_xunlock_((sx), LOCK_FILE, LOCK_LINE)
  260 #define sx_slock(sx)            sx_slock_((sx), LOCK_FILE, LOCK_LINE)
  261 #define sx_slock_sig(sx)        sx_slock_sig_((sx), LOCK_FILE, LOCK_LINE)
  262 #define sx_sunlock(sx)          sx_sunlock_((sx), LOCK_FILE, LOCK_LINE)
  263 #define sx_assert(sx, what)     sx_assert_((sx), (what), __FILE__, __LINE__)
  264 
  265 /*
  266  * Return a pointer to the owning thread if the lock is exclusively
  267  * locked.
  268  */
  269 #define sx_xholder(sx)                                                  \
  270         ((sx)->sx_lock & SX_LOCK_SHARED ? NULL :                        \
  271         (struct thread *)SX_OWNER((sx)->sx_lock))
  272 
  273 #define sx_xlocked(sx)                                                  \
  274         (((sx)->sx_lock & ~(SX_LOCK_FLAGMASK & ~SX_LOCK_SHARED)) ==     \
  275             (uintptr_t)curthread)
  276 
  277 #define sx_unlock_(sx, file, line) do {                                 \
  278         if (sx_xlocked(sx))                                             \
  279                 sx_xunlock_(sx, file, line);                            \
  280         else                                                            \
  281                 sx_sunlock_(sx, file, line);                            \
  282 } while (0)
  283 
  284 #define sx_unlock(sx)   sx_unlock_((sx), LOCK_FILE, LOCK_LINE)
  285 
  286 #define sx_sleep(chan, sx, pri, wmesg, timo)                            \
  287         _sleep((chan), &(sx)->lock_object, (pri), (wmesg), (timo))
  288 
  289 /*
  290  * Options passed to sx_init_flags().
  291  */
  292 #define SX_DUPOK                0x01
  293 #define SX_NOPROFILE            0x02
  294 #define SX_NOWITNESS            0x04
  295 #define SX_QUIET                0x08
  296 #define SX_NOADAPTIVE           0x10
  297 #define SX_RECURSE              0x20
  298 
  299 /*
  300  * Options passed to sx_*lock_hard().
  301  */
  302 #define SX_INTERRUPTIBLE        0x40
  303 
  304 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
  305 #define SA_LOCKED               LA_LOCKED
  306 #define SA_SLOCKED              LA_SLOCKED
  307 #define SA_XLOCKED              LA_XLOCKED
  308 #define SA_UNLOCKED             LA_UNLOCKED
  309 #define SA_RECURSED             LA_RECURSED
  310 #define SA_NOTRECURSED          LA_NOTRECURSED
  311 
  312 /* Backwards compatability. */
  313 #define SX_LOCKED               LA_LOCKED
  314 #define SX_SLOCKED              LA_SLOCKED
  315 #define SX_XLOCKED              LA_XLOCKED
  316 #define SX_UNLOCKED             LA_UNLOCKED
  317 #define SX_RECURSED             LA_RECURSED
  318 #define SX_NOTRECURSED          LA_NOTRECURSED
  319 #endif
  320 
  321 #endif /* _KERNEL */
  322 
  323 #endif /* !_SYS_SX_H_ */

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