sys/sys/lock.h

   1 /*
   2  * Copyright (c) 1995
   3  *      The Regents of the University of California.  All rights reserved.
   4  * Copyright (c) 2013-2017
   5  *      The DragonFly Project.  All rights reserved.
   6  *
   7  * This code contains ideas from software contributed to Berkeley by
   8  * Avadis Tevanian, Jr., Michael Wayne Young, and the Mach Operating
   9  * System project at Carnegie-Mellon University.
  10  *
  11  * This code is derived from software contributed to The DragonFly Project
  12  * by Matthew Dillon <dillon@backplane.com>
  13  *
  14  * Redistribution and use in source and binary forms, with or without
  15  * modification, are permitted provided that the following conditions
  16  * are met:
  17  * 1. Redistributions of source code must retain the above copyright
  18  *    notice, this list of conditions and the following disclaimer.
  19  * 2. Redistributions in binary form must reproduce the above copyright
  20  *    notice, this list of conditions and the following disclaimer in the
  21  *    documentation and/or other materials provided with the distribution.
  22  * 3. Neither the name of the University nor the names of its contributors
  23  *    may be used to endorse or promote products derived from this software
  24  *    without specific prior written permission.
  25  *
  26  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  27  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  28  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  29  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  30  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  31  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  32  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  33  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  34  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  35  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  36  * SUCH DAMAGE.
  37  */
  38
  39 #ifndef _SYS_LOCK_H_
  40 #define _SYS_LOCK_H_
  41
  42 /*
  43  * A number of third party programs #include <sys/lock.h> for no good
  44  * reason.  Don't actually include anything unless we are the kernel.
  45  */
  46 #if defined(_KERNEL) || defined(_KERNEL_STRUCTURES)
  47
  48 #include <machine/lock.h>
  49 #ifndef _SYS_THREAD_H_
  50 #include <sys/thread.h>         /* lwkt_token */
  51 #endif
  52 #ifndef _SYS_SPINLOCK_H_
  53 #include <sys/spinlock.h>
  54 #endif
  55
  56 /*
  57  * The general lock structure.  Provides for multiple shared locks,
  58  * upgrading from shared to exclusive, and sleeping until the lock
  59  * can be gained.
  60  *
  61  * NOTE: We don't __cachealign struct lock, its too much bloat.  Users
  62  *       of struct lock may be able to arrange it within greater structures
  63  *       in more SMP-friendly ways.
  64  */
  65 struct thread;
  66
  67 struct lock {
  68         u_int   lk_flags;               /* see below */
  69         int     lk_timo;                /* maximum sleep time (for tsleep) */
  70         uint64_t lk_count;              /* see LKC_* bits */
  71         const char *lk_wmesg;           /* resource sleeping (for tsleep) */
  72         struct thread *lk_lockholder;   /* thread of excl lock holder */
  73 };
  74
  75 /*
  76  * Lock request types:
  77  *
  78  *   LK_SHARED
  79  *      Get one of many possible shared locks. If a process holding an
  80  *      exclusive lock requests a shared lock, the exclusive lock(s) will
  81  *      be downgraded to shared locks.
  82  *
  83  *   LK_EXCLUSIVE
  84  *      Stop further shared locks, when they are cleared, grant a pending
  85  *      upgrade if it exists, then grant an exclusive lock. Only one exclusive
  86  *      lock may exist at a time, except that a process holding an exclusive
  87  *      lock may get additional exclusive locks if it explicitly sets the
  88  *      LK_CANRECURSE flag in the lock request, or if the LK_CANRECURSE flag
  89  *      was set when the lock was initialized.
  90  *
  91  *   LK_UPGRADE
  92  *      The process must hold a shared lock that it wants to have upgraded
  93  *      to an exclusive lock. Other processes may get exclusive access to
  94  *      the resource between the time that the upgrade is requested and the
  95  *      time that it is granted.
  96  *
  97  *   LK_EXCLUPGRADE
  98  *      the process must hold a shared lock that it wants to have upgraded
  99  *      to an exclusive lock. If the request succeeds, no other processes
 100  *      will have gotten exclusive access to the resource between the time
 101  *      that the upgrade is requested and the time that it is granted.
 102  *      However, if another process has already requested an upgrade, the
 103  *      request will fail (see error returns below).
 104  *
 105  *   LK_DOWNGRADE
 106  *      The process must hold an exclusive lock that it wants to have
 107  *      downgraded to a shared lock. If the process holds multiple (recursive)
 108  *      exclusive locks, they will all be downgraded to shared locks.
 109  *
 110  *   LK_RELEASE
 111  *      Release one instance of a lock.
 112  *
 113  *   LK_CANCEL_BEG
 114  *      The current exclusive lock holder can cancel any blocked lock requests,
 115  *      or any new requests, whos callers specified LK_CANCELABLE.  They will
 116  *      receive a ENOLCK error code.  Cancel beg/end does not stack.
 117  *
 118  *      The cancel command stays in effect until the exclusive lock holder
 119  *      releases the last count on the lock or issues a LK_CANCEL_END command.
 120  *
 121  *   LK_CANCEL_END
 122  *      The current exclusive lock holder can stop canceling new requests
 123  *      whos callers specify LK_CANCELABLE.  The exclusive lock is maintained.
 124  *
 125  *      Note that the last release of the exclusive lock will also
 126  *      automatically end cancel mode.
 127  *
 128  *
 129  * ---
 130  *
 131  *   LK_EXCLOTHER - return for lockstatus().  Used when another process
 132  *      holds the lock exclusively.
 133  *
 134  * These are flags that are passed to the lockmgr routine.
 135  */
 136 #define LK_TYPE_MASK    0x0000000f      /* type of lock sought */
 137 #define LK_SHARED       0x00000001      /* shared lock */
 138 #define LK_EXCLUSIVE    0x00000002      /* exclusive lock */
 139 #define LK_UPGRADE      0x00000003      /* shared-to-exclusive upgrade */
 140 #define LK_EXCLUPGRADE  0x00000004      /* first shared-to-exclusive upgrade */
 141 #define LK_DOWNGRADE    0x00000005      /* exclusive-to-shared downgrade */
 142 #define LK_RELEASE      0x00000006      /* release any type of lock */
 143 #define LK_WAITUPGRADE  0x00000007
 144 #define LK_EXCLOTHER    0x00000008      /* other process holds lock */
 145 #define LK_CANCEL_BEG   0x00000009      /* cancel other requests */
 146 #define LK_CANCEL_END   0x0000000a      /* stop canceling other requests */
 147
 148 /*
 149  * lk_count bit fields.
 150  *
 151  * Positive count is exclusive, negative count is shared.  The count field
 152  * must be large enough to accomodate all possible threads.
 153  */
 154 #define LKC_RESERVED8   0x0000000080000000LU    /* (DNU, insn optimization) */
 155 #define LKC_EXREQ       0x0000000040000000LU    /* waiting for excl lock */
 156 #define LKC_SHARED      0x0000000020000000LU    /* shared lock(s) granted */
 157 #define LKC_UPREQ       0x0000000010000000LU    /* waiting for upgrade */
 158 #define LKC_EXREQ2      0x0000000008000000LU    /* multi-wait for EXREQ */
 159 #define LKC_CANCEL      0x0000000004000000LU    /* cancel in effect */
 160 #define LKC_XMASK       0x0000000003FFFFFFLU
 161 #define LKC_SMASK       0xFFFFFFFF00000000LU
 162 #define LKC_SCOUNT      0x0000000100000000LU
 163 #define LKC_SSHIFT      32
 164
 165 /*
 166  * External lock flags.
 167  *
 168  * The first three flags may be set in lock_init to set their mode permanently,
 169  * or passed in as arguments to the lock manager.
 170  */
 171 #define LK_EXTFLG_MASK  0x070000F0      /* mask of external flags */
 172 #define LK_NOWAIT       0x00000010      /* do not sleep to await lock */
 173 #define LK_SLEEPFAIL    0x00000020      /* sleep, then return failure */
 174 #define LK_CANRECURSE   0x00000040      /* allow recursive exclusive lock */
 175 #define LK_NOCOLLSTATS  0x00000080      /* v_lock_coll not applicable */
 176 #define LK_CANCELABLE   0x01000000      /* blocked caller can be canceled */
 177 #define LK_TIMELOCK     0x02000000
 178 #define LK_PCATCH       0x04000000      /* timelocked with signal catching */
 179
 180 /*
 181  * Control flags
 182  *
 183  * Non-persistent external flags.
 184  */
 185 #define LK_FAILRECLAIM  0x00010000 /* vn_lock: allowed to fail on reclaim */
 186 #define LK_RETRY        0x00020000 /* vn_lock: retry until locked */
 187 #define LK_UNUSED40000  0x00040000
 188 #define LK_UNUSED80000  0x00080000
 189
 190 /*
 191  * Lock return status.
 192  *
 193  * Successfully obtained locks return 0. Locks will always succeed
 194  * unless one of the following is true:
 195  *      LK_FORCEUPGRADE is requested and some other process has already
 196  *          requested a lock upgrade (returns EBUSY).
 197  *      LK_WAIT is set and a sleep would be required (returns EBUSY).
 198  *      LK_SLEEPFAIL is set and a sleep was done (returns ENOLCK).
 199  *      PCATCH is set in lock priority and a signal arrives (returns
 200  *          either EINTR or ERESTART if system calls is to be restarted).
 201  *      Non-null lock timeout and timeout expires (returns EWOULDBLOCK).
 202  * A failed lock attempt always returns a non-zero error value. No lock
 203  * is held after an error return (in particular, a failed LK_UPGRADE
 204  * or LK_FORCEUPGRADE will have released its shared access lock).
 205  */
 206
 207 /*
 208  * Indicator that no process holds exclusive lock
 209  */
 210 #define LK_KERNTHREAD ((struct thread *)-2)
 211
 212 #ifdef _KERNEL
 213
 214 void dumplockinfo(struct lock *lkp);
 215 struct proc;
 216
 217 struct lock_args {
 218         struct lock     *la_lock;
 219         const char      *la_desc;
 220         int             la_flags;
 221 };
 222
 223 #define LOCK_INITIALIZER(wmesg, timo, flags)    \
 224 {                                               \
 225         .lk_flags = ((flags) & LK_EXTFLG_MASK), \
 226         .lk_timo = (timo),                      \
 227         .lk_count = 0,                          \
 228         .lk_wmesg = wmesg,                      \
 229         .lk_lockholder = NULL                   \
 230 }
 231
 232 void    lockinit (struct lock *, const char *wmesg, int timo, int flags);
 233 void    lockreinit (struct lock *, const char *wmesg, int timo, int flags);
 234 void    lockuninit(struct lock *);
 235 void    lock_sysinit(struct lock_args *);
 236 int     lockmgr_shared (struct lock *, u_int flags);
 237 int     lockmgr_exclusive (struct lock *, u_int flags);
 238 int     lockmgr_downgrade (struct lock *, u_int flags);
 239 int     lockmgr_upgrade (struct lock *, u_int flags);
 240 int     lockmgr_release (struct lock *, u_int flags);
 241 int     lockmgr_cancel_beg (struct lock *, u_int flags);
 242 int     lockmgr_cancel_end (struct lock *, u_int flags);
 243 void    lockmgr_kernproc (struct lock *);
 244 void    lockmgr_printinfo (struct lock *);
 245 int     lockstatus (struct lock *, struct thread *);
 246 int     lockowned (struct lock *);
 247
 248 #define LOCK_SYSINIT(name, lock, desc, flags)                           \
 249         static struct lock_args name##_args = {                         \
 250                 (lock),                                                 \
 251                 (desc),                                                 \
 252                 (flags)                                                 \
 253         };                                                              \
 254         SYSINIT(name##_lock_sysinit, SI_SUB_DRIVERS, SI_ORDER_MIDDLE,   \
 255             lock_sysinit, &name##_args);                                \
 256         SYSUNINIT(name##_lock_sysuninit, SI_SUB_DRIVERS, SI_ORDER_MIDDLE, \
 257             lockuninit, (lock))
 258
 259 /*
 260  * Most lockmgr() calls pass a constant flags parameter which
 261  * we can optimize-out with an inline.
 262  */
 263 static __inline
 264 int
 265 lockmgr(struct lock *lkp, u_int flags)
 266 {
 267         switch(flags & LK_TYPE_MASK) {
 268         case LK_SHARED:
 269                 return lockmgr_shared(lkp, flags);
 270         case LK_EXCLUSIVE:
 271                 return lockmgr_exclusive(lkp, flags);
 272         case LK_DOWNGRADE:
 273                 return lockmgr_downgrade(lkp, flags);
 274         case LK_EXCLUPGRADE:
 275         case LK_UPGRADE:
 276                 return lockmgr_upgrade(lkp, flags);
 277         case LK_RELEASE:
 278                 return lockmgr_release(lkp, flags);
 279         case LK_CANCEL_BEG:
 280                 return lockmgr_cancel_beg(lkp, flags);
 281         case LK_CANCEL_END:
 282                 return lockmgr_cancel_end(lkp, flags);
 283         default:
 284                 panic("lockmgr: unknown locktype request %d",
 285                       flags & LK_TYPE_MASK);
 286                 return EINVAL;  /* NOT REACHED */
 287         }
 288 }
 289
 290 /*
 291  * Returns non-zero if the lock is in-use.  Cannot be used to count
 292  * refs on a lock (refs cannot be safely counted due to the use of
 293  * atomic_fetchadd_int() for shared locks.
 294  */
 295 static __inline
 296 int
 297 lockinuse(struct lock *lkp)
 298 {
 299         return ((lkp->lk_count & (LKC_SMASK | LKC_XMASK)) != 0);
 300 }
 301
 302 /*
 303  * Returns true if the lock was acquired. Can be used to port
 304  * FreeBSD's mtx_trylock() and similar functions.
 305  */
 306 static __inline
 307 boolean_t
 308 lockmgr_try(struct lock *lkp, u_int flags)
 309 {
 310         return (lockmgr(lkp, flags | LK_NOWAIT) == 0);
 311 }
 312
 313 #endif /* _KERNEL */
 314 #endif /* _KERNEL || _KERNEL_STRUCTURES */
 315 #endif /* _SYS_LOCK_H_ */