1.\" 2.\" Copyright (C) 2002 Chad David <davidc@acns.ab.ca>. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice(s), this list of conditions and the following disclaimer as 9.\" the first lines of this file unmodified other than the possible 10.\" addition of one or more copyright notices. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice(s), this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY 16.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED 17.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE 18.\" DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY 19.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 20.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 21.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 22.\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH 25.\" DAMAGE. 26.\" 27.\" $FreeBSD$ 28.\" 29.Dd April 12, 2008 30.Dt LOCK 9 31.Os 32.Sh NAME 33.Nm lockinit , 34.Nm lockdestroy , 35.Nm lockmgr , 36.Nm lockmgr_args , 37.Nm lockmgr_args_rw , 38.Nm lockmgr_disown , 39.Nm lockmgr_printinfo , 40.Nm lockmgr_recursed , 41.Nm lockmgr_rw , 42.Nm lockmgr_waiters , 43.Nm lockstatus , 44.Nm lockmgr_assert 45.Nd "lockmgr family of functions" 46.Sh SYNOPSIS 47.In sys/types.h 48.In sys/lock.h 49.In sys/lockmgr.h 50.Ft void 51.Fn lockinit "struct lock *lkp" "int prio" "const char *wmesg" "int timo" "int flags" 52.Ft void 53.Fn lockdestroy "struct lock *lkp" 54.Ft int 55.Fn lockmgr "struct lock *lkp" "u_int flags" "struct mtx *ilk" 56.Ft int 57.Fn lockmgr_args "struct lock *lkp" "u_int flags" "struct mtx *ilk" "const char *wmesg" "int prio" "int timo" 58.Ft int 59.Fn lockmgr_args_rw "struct lock *lkp" "u_int flags" "struct rwlock *ilk" "const char *wmesg" "int prio" "int timo" 60.Ft void 61.Fn lockmgr_disown "struct lock *lkp" 62.Ft void 63.Fn lockmgr_printinfo "struct lock *lkp" 64.Ft int 65.Fn lockmgr_recursed "struct lock *lkp" 66.Ft int 67.Fn lockmgr_rw "struct lock *lkp" "u_int flags" "struct rwlock *ilk" 68.Ft int 69.Fn lockmgr_waiters "struct lock *lkp" 70.Ft int 71.Fn lockstatus "struct lock *lkp" 72.Pp 73.Cd "options INVARIANTS" 74.Cd "options INVARIANT_SUPPORT" 75.Ft void 76.Fn lockmgr_assert "struct lock *lkp" "int what" 77.Sh DESCRIPTION 78The 79.Fn lockinit 80function is used to initialize a lock. 81It must be called before any operation can be performed on a lock. 82Its arguments are: 83.Bl -tag -width ".Fa wmesg" 84.It Fa lkp 85A pointer to the lock to initialize. 86.It Fa prio 87The priority passed to 88.Xr sleep 9 . 89.It Fa wmesg 90The lock message. 91This is used for both debugging output and 92.Xr sleep 9 . 93.It Fa timo 94The timeout value passed to 95.Xr sleep 9 . 96.It Fa flags 97The flags the lock is to be initialized with: 98.Bl -tag -width ".Dv LK_CANRECURSE" 99.It Dv LK_CANRECURSE 100Allow recursive exclusive locks. 101.It Dv LK_NOPROFILE 102Disable lock profiling for this lock. 103.It Dv LK_NOSHARE 104Allow exclusive locks only. 105.It Dv LK_NOWITNESS 106Instruct 107.Xr witness 4 108to ignore this lock. 109.It Dv LK_NODUP 110.Xr witness 4 111should log messages about duplicate locks being acquired. 112.It Dv LK_QUIET 113Disable 114.Xr ktr 4 115logging for this lock. 116.It Dv LK_TIMELOCK 117Use 118.Fa timo 119during a sleep; otherwise, 0 is used. 120.El 121.El 122.Pp 123The 124.Fn lockdestroy 125function is used to destroy a lock, and while it is called in a number of 126places in the kernel, it currently does nothing. 127.Pp 128The 129.Fn lockmgr 130and 131.Fn lockmgr_rw 132functions handle general locking functionality within the kernel, including 133support for shared and exclusive locks, and recursion. 134.Fn lockmgr 135and 136.Fn lockmgr_rw 137are also able to upgrade and downgrade locks. 138.Pp 139Their arguments are: 140.Bl -tag -width ".Fa flags" 141.It Fa lkp 142A pointer to the lock to manipulate. 143.It Fa flags 144Flags indicating what action is to be taken. 145.Bl -tag -width ".Dv LK_CANRECURSE" 146.It Dv LK_SHARED 147Acquire a shared lock. 148If an exclusive lock is currently held, it will be downgraded. 149.It Dv LK_EXCLUSIVE 150Acquire an exclusive lock. 151If an exclusive lock is already held, and 152.Dv LK_CANRECURSE 153is not set, the system will 154.Xr panic 9 . 155.It Dv LK_DOWNGRADE 156Downgrade exclusive lock to a shared lock. 157Downgrading a shared lock is not permitted. 158If an exclusive lock has been recursed, all references will be downgraded. 159.It Dv LK_UPGRADE 160Upgrade a shared lock to an exclusive lock. 161If this call fails, the shared lock is lost. 162During the upgrade, the shared lock could 163be temporarily dropped. 164Attempts to upgrade an exclusive lock will cause a 165.Xr panic 9 . 166.It Dv LK_RELEASE 167Release the lock. 168Releasing a lock that is not held can cause a 169.Xr panic 9 . 170.It Dv LK_DRAIN 171Wait for all activity on the lock to end, then mark it decommissioned. 172This is used before freeing a lock that is part of a piece of memory that is 173about to be freed. 174(As documented in 175.In sys/lockmgr.h . ) 176.It Dv LK_SLEEPFAIL 177Fail if operation has slept. 178.It Dv LK_NOWAIT 179Do not allow the call to sleep. 180This can be used to test the lock. 181.It Dv LK_NOWITNESS 182Skip the 183.Xr witness 4 184checks for this instance. 185.It Dv LK_CANRECURSE 186Allow recursion on an exclusive lock. 187For every lock there must be a release. 188.It Dv LK_INTERLOCK 189Unlock the interlock (which should be locked already). 190.El 191.It Fa ilk 192An interlock mutex for controlling group access to the lock. 193If 194.Dv LK_INTERLOCK 195is specified, 196.Fn lockmgr 197and 198.Fn lockmgr_rw 199assume 200.Fa ilk 201is currently owned and not recursed, and will return it unlocked. 202See 203.Xr mtx_assert 9 . 204.El 205.Pp 206The 207.Fn lockmgr_args 208and 209.Fn lockmgr_args_rw 210function work like 211.Fn lockmgr 212and 213.Fn lockmgr_rw 214but accepting a 215.Fa wmesg , 216.Fa timo 217and 218.Fa prio 219on a per-instance basis. 220The specified values will override the default 221ones, but this can still be used passing, respectively, 222.Dv LK_WMESG_DEFAULT , 223.Dv LK_PRIO_DEFAULT 224and 225.Dv LK_TIMO_DEFAULT . 226.Pp 227The 228.Fn lockmgr_disown 229function switches the owner from the current thread to be 230.Dv LK_KERNPROC, 231if the lock is already held. 232.Pp 233The 234.Fn lockmgr_printinfo 235function prints debugging information about the lock. 236It is used primarily by 237.Xr VOP_PRINT 9 238functions. 239.Pp 240The 241.Fn lockmgr_recursed 242function returns true if the lock is recursed, 0 243otherwise. 244.Pp 245The 246.Fn lockmgr_waiters 247function returns true if the lock has waiters, 0 otherwise. 248.Pp 249The 250.Fn lockstatus 251function returns the status of the lock in relation to the current thread. 252.Pp 253When compiled with 254.Cd "options INVARIANTS" 255and 256.Cd "options INVARIANT_SUPPORT" , 257the 258.Fn lockmgr_assert 259function tests 260.Fa lkp 261for the assertions specified in 262.Fa what , 263and panics if they are not met. 264One of the following assertions must be specified: 265.Bl -tag -width ".Dv KA_UNLOCKED" 266.It Dv KA_LOCKED 267Assert that the current thread has either a shared or an exclusive lock on the 268.Vt lkp 269lock pointed to by the first argument. 270.It Dv KA_SLOCKED 271Assert that the current thread has a shared lock on the 272.Vt lkp 273lock pointed to by the first argument. 274.It Dv KA_XLOCKED 275Assert that the current thread has an exclusive lock on the 276.Vt lkp 277lock pointed to by the first argument. 278.It Dv KA_UNLOCKED 279Assert that the current thread has no lock on the 280.Vt lkp 281lock pointed to by the first argument. 282.It Dv KA_HELD 283Assert that an unspecified thread has a lock on the 284.Vt lkp 285lock pointed to by the first argument. 286.It Dv KA_UNHELD 287Assert that no thread has a lock on the 288.Vt lkp 289lock pointed to by the first argument. 290.El 291.Pp 292In addition, one of the following optional assertions can be used with 293either an 294.Dv KA_LOCKED , 295.Dv KA_SLOCKED , 296or 297.Dv KA_XLOCKED 298assertion: 299.Bl -tag -width ".Dv KA_NOTRECURSED" 300.It Dv KA_RECURSED 301Assert that the current thread has a recursed lock on 302.Fa lkp . 303.It Dv KA_NOTRECURSED 304Assert that the current thread does not have a recursed lock on 305.Fa lkp . 306.El 307.Pp 308Note that 309.Dv KA_HELD 310and 311.Dv KA_UNHELD 312usage is highly discouraged. 313They are intended to cater a bad behaviour 314introduced by buffer cache lock handling. 315They will hopefully be 316made useless by revisiting such locks. 317.Sh RETURN VALUES 318The 319.Fn lockmgr 320and 321.Fn lockmgr_rw 322functions return 0 on success and non-zero on failure. 323.Pp 324The 325.Fn lockstatus 326function returns: 327.Bl -tag -width ".Dv LK_EXCLUSIVE" 328.It Dv LK_EXCLUSIVE 329An exclusive lock is held by the current thread. 330.It Dv LK_EXCLOTHER 331An exclusive lock is held by someone other than the current thread. 332.It Dv LK_SHARED 333A shared lock is held. 334.It Li 0 335The lock is not held by anyone. 336.El 337.Sh ERRORS 338.Fn lockmgr 339and 340.Fn lockmgr_rw 341fail if: 342.Bl -tag -width Er 343.It Bq Er EBUSY 344.Dv LK_FORCEUPGRADE 345was requested and another thread had already requested a lock upgrade. 346.It Bq Er EBUSY 347.Dv LK_NOWAIT 348was set, and a sleep would have been required. 349.It Bq Er ENOLCK 350.Dv LK_SLEEPFAIL 351was set and 352.Fn lockmgr 353or 354.Fn lockmgr_rw 355did sleep. 356.It Bq Er EINTR 357.Dv PCATCH 358was set in the lock priority, and a signal was delivered during a sleep. 359Note the 360.Er ERESTART 361error below. 362.It Bq Er ERESTART 363.Dv PCATCH 364was set in the lock priority, a signal was delivered during a sleep, 365and the system call is to be restarted. 366.It Bq Er EWOULDBLOCK 367a non-zero timeout was given, and the timeout expired. 368.El 369.Sh LOCKS 370If 371.Dv LK_INTERLOCK 372is passed in the 373.Fa flags 374argument to 375.Fn lockmgr 376or 377.Fn lockmgr_rw , 378the 379.Fa ilk 380must be held prior to calling 381.Fn lockmgr 382or 383.Fn lockmgr_rw , 384and will be returned unlocked. 385.Pp 386Upgrade attempts that fail result in the loss of the lock that 387is currently held. 388Also, it is invalid to upgrade an 389exclusive lock, and a 390.Xr panic 9 391will be the result of trying. 392.Sh SEE ALSO 393.Xr condvar 9 , 394.Xr locking 9 , 395.Xr mutex 9 , 396.Xr rwlock 9 , 397.Xr sleep 9 , 398.Xr sx 9 , 399.Xr mtx_assert 9 , 400.Xr panic 9 , 401.Xr VOP_PRINT 9 402.Sh AUTHORS 403This manual page was written by 404.An Chad David Aq davidc@acns.ab.ca . 405