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  * $FreeBSD$
   30  */
   31 
   32 #ifndef _SYS_SX_H_
   33 #define _SYS_SX_H_
   34 
   35 #include <sys/_lock.h>
   36 #include <sys/_sx.h>
   37 #include <sys/lock_profile.h>
   38 
   39 #ifdef  _KERNEL
   40 #include <machine/atomic.h>
   41 #endif
   42 
   43 /*
   44  * In general, the sx locks and rwlocks use very similar algorithms.
   45  * The main difference in the implementations is how threads are
   46  * blocked when a lock is unavailable.  For this, sx locks use sleep
   47  * queues which do not support priority propagation, and rwlocks use
   48  * turnstiles which do.
   49  *
   50  * The sx_lock field consists of several fields.  The low bit
   51  * indicates if the lock is locked with a shared or exclusive lock.  A
   52  * value of 0 indicates an exclusive lock, and a value of 1 indicates
   53  * a shared lock.  Bit 1 is a boolean indicating if there are any
   54  * threads waiting for a shared lock.  Bit 2 is a boolean indicating
   55  * if there are any threads waiting for an exclusive lock.  Bit 3 is a
   56  * boolean indicating if an exclusive lock is recursively held.  The
   57  * rest of the variable's definition is dependent on the value of the
   58  * first bit.  For an exclusive lock, it is a pointer to the thread
   59  * holding the lock, similar to the mtx_lock field of mutexes.  For
   60  * shared locks, it is a count of read locks that are held.
   61  *
   62  * When the lock is not locked by any thread, it is encoded as a
   63  * shared lock with zero waiters.
   64  *
   65  * A note about memory barriers.  Exclusive locks need to use the same
   66  * memory barriers as mutexes: _acq when acquiring an exclusive lock
   67  * and _rel when releasing an exclusive lock.  On the other side,
   68  * shared lock needs to use an _acq barrier when acquiring the lock
   69  * but, since they don't update any locked data, no memory barrier is
   70  * needed when releasing a shared lock.
   71  */
   72 
   73 #define SX_LOCK_SHARED                  0x01
   74 #define SX_LOCK_SHARED_WAITERS          0x02
   75 #define SX_LOCK_EXCLUSIVE_WAITERS       0x04
   76 #define SX_LOCK_RECURSED                0x08
   77 #define SX_LOCK_FLAGMASK                                                \
   78         (SX_LOCK_SHARED | SX_LOCK_SHARED_WAITERS |                      \
   79         SX_LOCK_EXCLUSIVE_WAITERS | SX_LOCK_RECURSED)
   80 
   81 #define SX_OWNER(x)                     ((x) & ~SX_LOCK_FLAGMASK)
   82 #define SX_SHARERS_SHIFT                4
   83 #define SX_SHARERS(x)                   (SX_OWNER(x) >> SX_SHARERS_SHIFT)
   84 #define SX_SHARERS_LOCK(x)                                              \
   85         ((x) << SX_SHARERS_SHIFT | SX_LOCK_SHARED)
   86 #define SX_ONE_SHARER                   (1 << SX_SHARERS_SHIFT)
   87 
   88 #define SX_LOCK_UNLOCKED                SX_SHARERS_LOCK(0)
   89 #define SX_LOCK_DESTROYED                                               \
   90         (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)
   91 
   92 #ifdef _KERNEL
   93 
   94 /*
   95  * Function prototipes.  Routines that start with an underscore are not part
   96  * of the public interface and are wrappered with a macro.
   97  */
   98 void    sx_sysinit(void *arg);
   99 #define sx_init(sx, desc)       sx_init_flags((sx), (desc), 0)
  100 void    sx_init_flags(struct sx *sx, const char *description, int opts);
  101 void    sx_destroy(struct sx *sx);
  102 int     _sx_slock(struct sx *sx, int opts, const char *file, int line);
  103 int     _sx_xlock(struct sx *sx, int opts, const char *file, int line);
  104 int     _sx_try_slock(struct sx *sx, const char *file, int line);
  105 int     _sx_try_xlock(struct sx *sx, const char *file, int line);
  106 void    _sx_sunlock(struct sx *sx, const char *file, int line);
  107 void    _sx_xunlock(struct sx *sx, const char *file, int line);
  108 int     _sx_try_upgrade(struct sx *sx, const char *file, int line);
  109 void    _sx_downgrade(struct sx *sx, const char *file, int line);
  110 int     _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts,
  111             const char *file, int line);
  112 int     _sx_slock_hard(struct sx *sx, int opts, const char *file, int line);
  113 void    _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int
  114             line);
  115 void    _sx_sunlock_hard(struct sx *sx, const char *file, int line);
  116 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
  117 void    _sx_assert(struct sx *sx, int what, const char *file, int line);
  118 #endif
  119 #ifdef DDB
  120 int     sx_chain(struct thread *td, struct thread **ownerp);
  121 #endif
  122 
  123 struct sx_args {
  124         struct sx       *sa_sx;
  125         const char      *sa_desc;
  126 };
  127 
  128 #define SX_SYSINIT(name, sxa, desc)                                     \
  129         static struct sx_args name##_args = {                           \
  130                 (sxa),                                                  \
  131                 (desc)                                                  \
  132         };                                                              \
  133         SYSINIT(name##_sx_sysinit, SI_SUB_LOCK, SI_ORDER_MIDDLE,        \
  134             sx_sysinit, &name##_args);                                  \
  135         SYSUNINIT(name##_sx_sysuninit, SI_SUB_LOCK, SI_ORDER_MIDDLE,    \
  136             sx_destroy, (sxa))
  137 
  138 /*
  139  * Full lock operations that are suitable to be inlined in non-debug kernels.
  140  * If the lock can't be acquired or released trivially then the work is
  141  * deferred to 'tougher' functions.
  142  */
  143 
  144 /* Acquire an exclusive lock. */
  145 static __inline int
  146 __sx_xlock(struct sx *sx, struct thread *td, int opts, const char *file,
  147     int line)
  148 {
  149         uintptr_t tid = (uintptr_t)td;
  150         int error = 0;
  151 
  152         if (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid))
  153                 error = _sx_xlock_hard(sx, tid, opts, file, line);
  154         else
  155                 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0, file,
  156                     line);
  157 
  158         return (error);
  159 }
  160 
  161 /* Release an exclusive lock. */
  162 static __inline void
  163 __sx_xunlock(struct sx *sx, struct thread *td, const char *file, int line)
  164 {
  165         uintptr_t tid = (uintptr_t)td;
  166 
  167         if (!atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
  168                 _sx_xunlock_hard(sx, tid, file, line);
  169 }
  170 
  171 /* Acquire a shared lock. */
  172 static __inline int
  173 __sx_slock(struct sx *sx, int opts, const char *file, int line)
  174 {
  175         uintptr_t x = sx->sx_lock;
  176         int error = 0;
  177 
  178         if (!(x & SX_LOCK_SHARED) ||
  179             !atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER))
  180                 error = _sx_slock_hard(sx, opts, file, line);
  181 #ifdef LOCK_PROFILING_SHARED
  182         else if (SX_SHARERS(x) == 0)
  183                 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0, file,
  184                     line);
  185 #endif
  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  */
  197 static __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_ */

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