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/10.0/sys/sys/sx.h 247787 2013-03-04 12:48:41Z davide $
   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_try_slock_(struct sx *sx, const char *file, int line);
   98 int     sx_try_xlock_(struct sx *sx, const char *file, int line);
   99 int     sx_try_upgrade_(struct sx *sx, const char *file, int line);
  100 void    sx_downgrade_(struct sx *sx, const char *file, int line);
  101 int     _sx_slock(struct sx *sx, int opts, const char *file, int line);
  102 int     _sx_xlock(struct sx *sx, int opts, const char *file, int line);
  103 void    _sx_sunlock(struct sx *sx, const char *file, int line);
  104 void    _sx_xunlock(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(const 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 struct sx_args {
  119         struct sx       *sa_sx;
  120         const char      *sa_desc;
  121         int             sa_flags;
  122 };
  123 
  124 #define SX_SYSINIT_FLAGS(name, sxa, desc, flags)                        \
  125         static struct sx_args name##_args = {                           \
  126                 (sxa),                                                  \
  127                 (desc),                                                 \
  128                 (flags)                                                 \
  129         };                                                              \
  130         SYSINIT(name##_sx_sysinit, SI_SUB_LOCK, SI_ORDER_MIDDLE,        \
  131             sx_sysinit, &name##_args);                                  \
  132         SYSUNINIT(name##_sx_sysuninit, SI_SUB_LOCK, SI_ORDER_MIDDLE,    \
  133             sx_destroy, (sxa))
  134 
  135 #define SX_SYSINIT(name, sxa, desc)     SX_SYSINIT_FLAGS(name, sxa, desc, 0)
  136 
  137 /*
  138  * Full lock operations that are suitable to be inlined in non-debug kernels.
  139  * If the lock can't be acquired or released trivially then the work is
  140  * deferred to 'tougher' functions.
  141  */
  142 
  143 /* Acquire an exclusive lock. */
  144 static __inline int
  145 __sx_xlock(struct sx *sx, struct thread *td, int opts, const char *file,
  146     int line)
  147 {
  148         uintptr_t tid = (uintptr_t)td;
  149         int error = 0;
  150 
  151         if (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid))
  152                 error = _sx_xlock_hard(sx, tid, opts, file, line);
  153         else 
  154                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE,
  155                     sx, 0, 0, file, line);
  156 
  157         return (error);
  158 }
  159 
  160 /* Release an exclusive lock. */
  161 static __inline void
  162 __sx_xunlock(struct sx *sx, struct thread *td, const char *file, int line)
  163 {
  164         uintptr_t tid = (uintptr_t)td;
  165 
  166         if (!atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
  167                 _sx_xunlock_hard(sx, tid, file, line);
  168 }
  169 
  170 /* Acquire a shared lock. */
  171 static __inline int
  172 __sx_slock(struct sx *sx, int opts, const char *file, int line)
  173 {
  174         uintptr_t x = sx->sx_lock;
  175         int error = 0;
  176 
  177         if (!(x & SX_LOCK_SHARED) ||
  178             !atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER))
  179                 error = _sx_slock_hard(sx, opts, file, line);
  180         else
  181                 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx, 0,
  182                     0, file, line);
  183 
  184         return (error);
  185 }
  186 
  187 /*
  188  * Release a shared lock.  We can just drop a single shared lock so
  189  * long as we aren't trying to drop the last shared lock when other
  190  * threads are waiting for an exclusive lock.  This takes advantage of
  191  * the fact that an unlocked lock is encoded as a shared lock with a
  192  * count of 0.
  193  */
  194 static __inline void
  195 __sx_sunlock(struct sx *sx, const char *file, int line)
  196 {
  197         uintptr_t x = sx->sx_lock;
  198 
  199         if (x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS) ||
  200             !atomic_cmpset_rel_ptr(&sx->sx_lock, x, x - SX_ONE_SHARER))
  201                 _sx_sunlock_hard(sx, file, line);
  202 }
  203 
  204 /*
  205  * Public interface for lock operations.
  206  */
  207 #ifndef LOCK_DEBUG
  208 #error  "LOCK_DEBUG not defined, include <sys/lock.h> before <sys/sx.h>"
  209 #endif
  210 #if     (LOCK_DEBUG > 0) || defined(SX_NOINLINE)
  211 #define sx_xlock_(sx, file, line)                                       \
  212         (void)_sx_xlock((sx), 0, (file), (line))
  213 #define sx_xlock_sig_(sx, file, line)                                   \
  214         _sx_xlock((sx), SX_INTERRUPTIBLE, (file), (line))
  215 #define sx_xunlock_(sx, file, line)                                     \
  216         _sx_xunlock((sx), (file), (line))
  217 #define sx_slock_(sx, file, line)                                       \
  218         (void)_sx_slock((sx), 0, (file), (line))
  219 #define sx_slock_sig_(sx, file, line)                                   \
  220         _sx_slock((sx), SX_INTERRUPTIBLE, (file) , (line))
  221 #define sx_sunlock_(sx, file, line)                                     \
  222         _sx_sunlock((sx), (file), (line))
  223 #else
  224 #define sx_xlock_(sx, file, line)                                       \
  225         (void)__sx_xlock((sx), curthread, 0, (file), (line))
  226 #define sx_xlock_sig_(sx, file, line)                                   \
  227         __sx_xlock((sx), curthread, SX_INTERRUPTIBLE, (file), (line))
  228 #define sx_xunlock_(sx, file, line)                                     \
  229         __sx_xunlock((sx), curthread, (file), (line))
  230 #define sx_slock_(sx, file, line)                                       \
  231         (void)__sx_slock((sx), 0, (file), (line))
  232 #define sx_slock_sig_(sx, file, line)                                   \
  233         __sx_slock((sx), SX_INTERRUPTIBLE, (file), (line))
  234 #define sx_sunlock_(sx, file, line)                                     \
  235         __sx_sunlock((sx), (file), (line))
  236 #endif  /* LOCK_DEBUG > 0 || SX_NOINLINE */
  237 #define sx_try_slock(sx)        sx_try_slock_((sx), LOCK_FILE, LOCK_LINE)
  238 #define sx_try_xlock(sx)        sx_try_xlock_((sx), LOCK_FILE, LOCK_LINE)
  239 #define sx_try_upgrade(sx)      sx_try_upgrade_((sx), LOCK_FILE, LOCK_LINE)
  240 #define sx_downgrade(sx)        sx_downgrade_((sx), LOCK_FILE, LOCK_LINE)
  241 #ifdef INVARIANTS
  242 #define sx_assert_(sx, what, file, line)                                \
  243         _sx_assert((sx), (what), (file), (line))
  244 #else
  245 #define sx_assert_(sx, what, file, line)        (void)0
  246 #endif
  247 
  248 #define sx_xlock(sx)            sx_xlock_((sx), LOCK_FILE, LOCK_LINE)
  249 #define sx_xlock_sig(sx)        sx_xlock_sig_((sx), LOCK_FILE, LOCK_LINE)
  250 #define sx_xunlock(sx)          sx_xunlock_((sx), LOCK_FILE, LOCK_LINE)
  251 #define sx_slock(sx)            sx_slock_((sx), LOCK_FILE, LOCK_LINE)
  252 #define sx_slock_sig(sx)        sx_slock_sig_((sx), LOCK_FILE, LOCK_LINE)
  253 #define sx_sunlock(sx)          sx_sunlock_((sx), LOCK_FILE, LOCK_LINE)
  254 #define sx_assert(sx, what)     sx_assert_((sx), (what), __FILE__, __LINE__)
  255 
  256 /*
  257  * Return a pointer to the owning thread if the lock is exclusively
  258  * locked.
  259  */
  260 #define sx_xholder(sx)                                                  \
  261         ((sx)->sx_lock & SX_LOCK_SHARED ? NULL :                        \
  262         (struct thread *)SX_OWNER((sx)->sx_lock))
  263 
  264 #define sx_xlocked(sx)                                                  \
  265         (((sx)->sx_lock & ~(SX_LOCK_FLAGMASK & ~SX_LOCK_SHARED)) ==     \
  266             (uintptr_t)curthread)
  267 
  268 #define sx_unlock_(sx, file, line) do {                                 \
  269         if (sx_xlocked(sx))                                             \
  270                 sx_xunlock_(sx, file, line);                            \
  271         else                                                            \
  272                 sx_sunlock_(sx, file, line);                            \
  273 } while (0)
  274 
  275 #define sx_unlock(sx)   sx_unlock_((sx), LOCK_FILE, LOCK_LINE)
  276 
  277 #define sx_sleep(chan, sx, pri, wmesg, timo)                            \
  278         _sleep((chan), &(sx)->lock_object, (pri), (wmesg),              \
  279             tick_sbt * (timo), 0,  C_HARDCLOCK)
  280 
  281 /*
  282  * Options passed to sx_init_flags().
  283  */
  284 #define SX_DUPOK                0x01
  285 #define SX_NOPROFILE            0x02
  286 #define SX_NOWITNESS            0x04
  287 #define SX_QUIET                0x08
  288 #define SX_NOADAPTIVE           0x10
  289 #define SX_RECURSE              0x20
  290 
  291 /*
  292  * Options passed to sx_*lock_hard().
  293  */
  294 #define SX_INTERRUPTIBLE        0x40
  295 
  296 #if defined(INVARIANTS) || defined(INVARIANT_SUPPORT)
  297 #define SA_LOCKED               LA_LOCKED
  298 #define SA_SLOCKED              LA_SLOCKED
  299 #define SA_XLOCKED              LA_XLOCKED
  300 #define SA_UNLOCKED             LA_UNLOCKED
  301 #define SA_RECURSED             LA_RECURSED
  302 #define SA_NOTRECURSED          LA_NOTRECURSED
  303 
  304 /* Backwards compatability. */
  305 #define SX_LOCKED               LA_LOCKED
  306 #define SX_SLOCKED              LA_SLOCKED
  307 #define SX_XLOCKED              LA_XLOCKED
  308 #define SX_UNLOCKED             LA_UNLOCKED
  309 #define SX_RECURSED             LA_RECURSED
  310 #define SX_NOTRECURSED          LA_NOTRECURSED
  311 #endif
  312 
  313 #endif /* _KERNEL */
  314 
  315 #endif /* !_SYS_SX_H_ */

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