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: head/share/man/man9/lock.9 177697 2008-03-28 21:30:37Z brueffer $
28.\"
29.Dd March 28, 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_disown ,
38.Nm lockmgr_printinfo ,
39.Nm lockmgr_recursed ,
40.Nm lockmgr_waiters ,
41.Nm lockstatus ,
42.Nm lockmgr_assert
43.Nd "lockmgr family of functions"
44.Sh SYNOPSIS
45.In sys/types.h
46.In sys/lock.h
47.In sys/lockmgr.h
48.Ft void
49.Fn lockinit "struct lock *lkp" "int prio" "const char *wmesg" "int timo" "int flags"
50.Ft void
51.Fn lockdestroy "struct lock *lkp"
52.Ft int
53.Fn lockmgr "struct lock *lkp" "u_int flags" "struct mtx *interlkp"
54.Ft int
55.Fn lockmgr_args "struct lock *lkp" "u_int flags" "struct mtx *interlkp" "const char *wmesg" "int prio" "int timo"
56.Ft void
57.Fn lockmgr_disown "struct lock *lkp"
58.Ft void
59.Fn lockmgr_printinfo "struct lock *lkp"
60.Ft int
61.Fn lockmgr_recursed "struct lock *lkp"
62.Ft int
63.Fn lockmgr_waiters "struct lock *lkp"
64.Ft int
65.Fn lockstatus "struct lock *lkp"
66.Pp
67.Cd "options INVARIANTS"
68.Cd "options INVARIANT_SUPPORT"
69.Ft void
70.Fn lockmgr_assert "struct lock *lkp" "int what"
71.Sh DESCRIPTION
72The
73.Fn lockinit
74function is used to initialize a lock.
75It must be called before any operation can be performed on a lock.
76Its arguments are:
77.Bl -tag -width ".Fa wmesg"
78.It Fa lkp
79A pointer to the lock to initialize.
80.It Fa prio
81The priority passed to
82.Xr sleep 9 .
83.It Fa wmesg
84The lock message.
85This is used for both debugging output and
86.Xr sleep 9 .
87.It Fa timo
88The timeout value passed to
89.Xr sleep 9 .
90.It Fa flags
91The flags the lock is to be initialized with:
92.Bl -tag -width ".Dv LK_CANRECURSE"
93.It Dv LK_CANRECURSE
94Allow recursive exclusive locks.
95.It Dv LK_NOPROFILE
96Disable lock profiling for this lock.
97.It Dv LK_NOSHARE
98Allow exclusive locks only.
99.It Dv LK_NOWITNESS
100Instruct
101.Xr witness 4
102to ignore this lock.
103.It Dv LK_NODUP
104.Xr witness 4
105should log messages about duplicate locks being acquired.
106.It Dv LK_QUIET
107Disable
108.Xr ktr 4
109logging for this lock.
110.It Dv LK_TIMELOCK
111Use
112.Fa timo
113during a sleep; otherwise, 0 is used.
114.El
115.El
116.Pp
117The
118.Fn lockdestroy
119function is used to destroy a lock, and while it is called in a number of
120places in the kernel, it currently does nothing.
121.Pp
122The
123.Fn lockmgr
124function handles general locking functionality within the kernel, including
125support for shared and exclusive locks, and recursion.
126.Fn lockmgr
127is also able to upgrade and downgrade locks.
128.Pp
129Its arguments are:
130.Bl -tag -width ".Fa interlkp"
131.It Fa lkp
132A pointer to the lock to manipulate.
133.It Fa flags
134Flags indicating what action is to be taken.
135.Bl -tag -width ".Dv LK_CANRECURSE"
136.It Dv LK_SHARED
137Acquire a shared lock.
138If an exclusive lock is currently held, it will be downgraded.
139.It Dv LK_EXCLUSIVE
140Acquire an exclusive lock.
141If an exclusive lock is already held, and
142.Dv LK_CANRECURSE
143is not set, the system will
144.Xr panic 9 .
145.It Dv LK_DOWNGRADE
146Downgrade exclusive lock to a shared lock.
147Downgrading a shared lock is not permitted.
148If an exclusive lock has been recursed, all references will be downgraded.
149.It Dv LK_UPGRADE
150Upgrade a shared lock to an exclusive lock.
151If this call fails, the shared lock is lost.
152During the upgrade, the shared lock could
153be temporarily dropped.
154Attempts to upgrade an exclusive lock will cause a
155.Xr panic 9 .
156.It Dv LK_RELEASE
157Release the lock.
158Releasing a lock that is not held can cause a
159.Xr panic 9 .
160.It Dv LK_DRAIN
161Wait for all activity on the lock to end, then mark it decommissioned.
162This is used before freeing a lock that is part of a piece of memory that is
163about to be freed.
164(As documented in
165.In sys/lockmgr.h . )
166.It Dv LK_SLEEPFAIL
167Fail if operation has slept.
168.It Dv LK_NOWAIT
169Do not allow the call to sleep.
170This can be used to test the lock.
171.It Dv LK_CANRECURSE
172Allow recursion on an exclusive lock.
173For every lock there must be a release.
174.It Dv LK_INTERLOCK
175Unlock the interlock (which should be locked already).
176.El
177.It Fa interlkp
178An interlock mutex for controlling group access to the lock.
179If
180.Dv LK_INTERLOCK
181is specified,
182.Fn lockmgr
183assumes
184.Fa interlkp
185is currently owned and not recursed, and will return it unlocked.
186See
187.Xr mtx_assert 9 .
188.El
189.Pp
190The
191.Fn lockmgr_args
192function works like
193.Fn lockmgr
194but accepting a
195.Fa wmesg ,
196.Fa timo
197and
198.Fa prio
199on a per-instance basis.
200The specified values will override the default
201ones, but this can still be used passing, respectively,
202.Dv LK_WMESG_DEFAULT ,
203.Dv LK_PRIO_DEFAULT
204and
205.Dv LK_TIMO_DEFAULT .
206.Pp
207The
208.Fn lockmgr_disown
209function switches the owner from the current thread to be
210.Dv LK_KERNPROC,
211if the lock is already held.
212.Pp
213The
214.Fn lockmgr_printinfo
215function prints debugging information about the lock.
216It is used primarily by
217.Xr VOP_PRINT 9
218functions.
219.Pp
220The
221.Fn lockmgr_recursed
222function returns true if the lock is recursed, 0
223otherwise.
224.Pp
225The
226.Fn lockmgr_waiters
227function returns true if the lock has waiters, 0 otherwise.
228.Pp
229The
230.Fn lockstatus
231function returns the status of the lock in relation to the current thread.
232.Pp
233When compiled with
234.Cd "options INVARIANTS"
235and
236.Cd "options INVARIANT_SUPPORT" ,
237the
238.Fn lockmgr_assert
239function tests
240.Fa lkp
241for the assertions specified in
242.Fa what ,
243and panics if they are not met.
244One of the following assertions must be specified:
245.Bl -tag -width ".Dv KA_UNLOCKED"
246.It Dv KA_LOCKED
247Assert that the current thread has either a shared or an exclusive lock on the
248.Vt lkp
249lock pointed to by the first argument.
250.It Dv KA_SLOCKED
251Assert that the current thread has a shared lock on the
252.Vt lkp
253lock pointed to by the first argument.
254.It Dv KA_XLOCKED
255Assert that the current thread has an exclusive lock on the
256.Vt lkp
257lock pointed to by the first argument.
258.It Dv KA_UNLOCKED
259Assert that the current thread has no lock on the
260.Vt lkp
261lock pointed to by the first argument.
262.It Dv KA_HELD
263Assert that an unspecified thread has a lock on the
264.Vt lkp
265lock pointed to by the first argument.
266.It Dv KA_UNHELD
267Assert that no thread has a lock on the
268.Vt lkp
269lock pointed to by the first argument.
270.El
271.Pp
272In addition, one of the following optional assertions can be used with
273either an
274.Dv KA_LOCKED ,
275.Dv KA_SLOCKED ,
276or
277.Dv KA_XLOCKED
278assertion:
279.Bl -tag -width ".Dv KA_NOTRECURSED"
280.It Dv KA_RECURSED
281Assert that the current thread has a recursed lock on
282.Fa lkp .
283.It Dv KA_NOTRECURSED
284Assert that the current thread does not have a recursed lock on
285.Fa lkp .
286.El
287.Pp
288Note that
289.Dv KA_HELD
290and
291.Dv KA_UNHELD
292usage is highly discouraged.
293They are intended to cater a bad behaviour
294introduced by buffer cache lock handling.
295They will hopefully be
296made useless by revisiting such locks.
297.Sh RETURN VALUES
298The
299.Fn lockmgr
300function returns 0 on success and non-zero on failure.
301.Pp
302The
303.Fn lockstatus
304function returns:
305.Bl -tag -width ".Dv LK_EXCLUSIVE"
306.It Dv LK_EXCLUSIVE
307An exclusive lock is held by the current thread.
308.It Dv LK_EXCLOTHER
309An exclusive lock is held by someone other than the current thread.
310.It Dv LK_SHARED
311A shared lock is held.
312.It Li 0
313The lock is not held by anyone.
314.El
315.Sh ERRORS
316.Fn lockmgr
317fails if:
318.Bl -tag -width Er
319.It Bq Er EBUSY
320.Dv LK_FORCEUPGRADE
321was requested and another thread had already requested a lock upgrade.
322.It Bq Er EBUSY
323.Dv LK_NOWAIT
324was set, and a sleep would have been required.
325.It Bq Er ENOLCK
326.Dv LK_SLEEPFAIL
327was set and
328.Fn lockmgr
329did sleep.
330.It Bq Er EINTR
331.Dv PCATCH
332was set in the lock priority, and a signal was delivered during a sleep.
333Note the
334.Er ERESTART
335error below.
336.It Bq Er ERESTART
337.Dv PCATCH
338was set in the lock priority, a signal was delivered during a sleep,
339and the system call is to be restarted.
340.It Bq Er EWOULDBLOCK
341a non-zero timeout was given, and the timeout expired.
342.El
343.Sh LOCKS
344If
345.Dv LK_INTERLOCK
346is passed in the
347.Fa flags
348argument to
349.Fn lockmgr ,
350the
351.Fa interlkp
352must be held prior to calling
353.Fn lockmgr ,
354and will be returned unlocked.
355.Pp
356Upgrade attempts that fail result in the loss of the lock that
357is currently held.
358Also, it is invalid to upgrade an
359exclusive lock, and a
360.Xr panic 9
361will be the result of trying.
362.Sh SEE ALSO
363.Xr condvar 9 ,
364.Xr locking 9 ,
365.Xr mutex 9 ,
366.Xr rwlock 9 ,
367.Xr sleep 9 ,
368.Xr sx 9 ,
369.Xr mtx_assert 9 ,
370.Xr panic 9 ,
371.Xr VOP_PRINT 9
372.Sh AUTHORS
373This manual page was written by
374.An Chad David Aq davidc@acns.ab.ca .
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: head/share/man/man9/lock.9 177697 2008-03-28 21:30:37Z brueffer $
28.\"
29.Dd March 28, 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_disown ,
38.Nm lockmgr_printinfo ,
39.Nm lockmgr_recursed ,
40.Nm lockmgr_waiters ,
41.Nm lockstatus ,
42.Nm lockmgr_assert
43.Nd "lockmgr family of functions"
44.Sh SYNOPSIS
45.In sys/types.h
46.In sys/lock.h
47.In sys/lockmgr.h
48.Ft void
49.Fn lockinit "struct lock *lkp" "int prio" "const char *wmesg" "int timo" "int flags"
50.Ft void
51.Fn lockdestroy "struct lock *lkp"
52.Ft int
53.Fn lockmgr "struct lock *lkp" "u_int flags" "struct mtx *interlkp"
54.Ft int
55.Fn lockmgr_args "struct lock *lkp" "u_int flags" "struct mtx *interlkp" "const char *wmesg" "int prio" "int timo"
56.Ft void
57.Fn lockmgr_disown "struct lock *lkp"
58.Ft void
59.Fn lockmgr_printinfo "struct lock *lkp"
60.Ft int
61.Fn lockmgr_recursed "struct lock *lkp"
62.Ft int
63.Fn lockmgr_waiters "struct lock *lkp"
64.Ft int
65.Fn lockstatus "struct lock *lkp"
66.Pp
67.Cd "options INVARIANTS"
68.Cd "options INVARIANT_SUPPORT"
69.Ft void
70.Fn lockmgr_assert "struct lock *lkp" "int what"
71.Sh DESCRIPTION
72The
73.Fn lockinit
74function is used to initialize a lock.
75It must be called before any operation can be performed on a lock.
76Its arguments are:
77.Bl -tag -width ".Fa wmesg"
78.It Fa lkp
79A pointer to the lock to initialize.
80.It Fa prio
81The priority passed to
82.Xr sleep 9 .
83.It Fa wmesg
84The lock message.
85This is used for both debugging output and
86.Xr sleep 9 .
87.It Fa timo
88The timeout value passed to
89.Xr sleep 9 .
90.It Fa flags
91The flags the lock is to be initialized with:
92.Bl -tag -width ".Dv LK_CANRECURSE"
93.It Dv LK_CANRECURSE
94Allow recursive exclusive locks.
95.It Dv LK_NOPROFILE
96Disable lock profiling for this lock.
97.It Dv LK_NOSHARE
98Allow exclusive locks only.
99.It Dv LK_NOWITNESS
100Instruct
101.Xr witness 4
102to ignore this lock.
103.It Dv LK_NODUP
104.Xr witness 4
105should log messages about duplicate locks being acquired.
106.It Dv LK_QUIET
107Disable
108.Xr ktr 4
109logging for this lock.
110.It Dv LK_TIMELOCK
111Use
112.Fa timo
113during a sleep; otherwise, 0 is used.
114.El
115.El
116.Pp
117The
118.Fn lockdestroy
119function is used to destroy a lock, and while it is called in a number of
120places in the kernel, it currently does nothing.
121.Pp
122The
123.Fn lockmgr
124function handles general locking functionality within the kernel, including
125support for shared and exclusive locks, and recursion.
126.Fn lockmgr
127is also able to upgrade and downgrade locks.
128.Pp
129Its arguments are:
130.Bl -tag -width ".Fa interlkp"
131.It Fa lkp
132A pointer to the lock to manipulate.
133.It Fa flags
134Flags indicating what action is to be taken.
135.Bl -tag -width ".Dv LK_CANRECURSE"
136.It Dv LK_SHARED
137Acquire a shared lock.
138If an exclusive lock is currently held, it will be downgraded.
139.It Dv LK_EXCLUSIVE
140Acquire an exclusive lock.
141If an exclusive lock is already held, and
142.Dv LK_CANRECURSE
143is not set, the system will
144.Xr panic 9 .
145.It Dv LK_DOWNGRADE
146Downgrade exclusive lock to a shared lock.
147Downgrading a shared lock is not permitted.
148If an exclusive lock has been recursed, all references will be downgraded.
149.It Dv LK_UPGRADE
150Upgrade a shared lock to an exclusive lock.
151If this call fails, the shared lock is lost.
152During the upgrade, the shared lock could
153be temporarily dropped.
154Attempts to upgrade an exclusive lock will cause a
155.Xr panic 9 .
156.It Dv LK_RELEASE
157Release the lock.
158Releasing a lock that is not held can cause a
159.Xr panic 9 .
160.It Dv LK_DRAIN
161Wait for all activity on the lock to end, then mark it decommissioned.
162This is used before freeing a lock that is part of a piece of memory that is
163about to be freed.
164(As documented in
165.In sys/lockmgr.h . )
166.It Dv LK_SLEEPFAIL
167Fail if operation has slept.
168.It Dv LK_NOWAIT
169Do not allow the call to sleep.
170This can be used to test the lock.
171.It Dv LK_CANRECURSE
172Allow recursion on an exclusive lock.
173For every lock there must be a release.
174.It Dv LK_INTERLOCK
175Unlock the interlock (which should be locked already).
176.El
177.It Fa interlkp
178An interlock mutex for controlling group access to the lock.
179If
180.Dv LK_INTERLOCK
181is specified,
182.Fn lockmgr
183assumes
184.Fa interlkp
185is currently owned and not recursed, and will return it unlocked.
186See
187.Xr mtx_assert 9 .
188.El
189.Pp
190The
191.Fn lockmgr_args
192function works like
193.Fn lockmgr
194but accepting a
195.Fa wmesg ,
196.Fa timo
197and
198.Fa prio
199on a per-instance basis.
200The specified values will override the default
201ones, but this can still be used passing, respectively,
202.Dv LK_WMESG_DEFAULT ,
203.Dv LK_PRIO_DEFAULT
204and
205.Dv LK_TIMO_DEFAULT .
206.Pp
207The
208.Fn lockmgr_disown
209function switches the owner from the current thread to be
210.Dv LK_KERNPROC,
211if the lock is already held.
212.Pp
213The
214.Fn lockmgr_printinfo
215function prints debugging information about the lock.
216It is used primarily by
217.Xr VOP_PRINT 9
218functions.
219.Pp
220The
221.Fn lockmgr_recursed
222function returns true if the lock is recursed, 0
223otherwise.
224.Pp
225The
226.Fn lockmgr_waiters
227function returns true if the lock has waiters, 0 otherwise.
228.Pp
229The
230.Fn lockstatus
231function returns the status of the lock in relation to the current thread.
232.Pp
233When compiled with
234.Cd "options INVARIANTS"
235and
236.Cd "options INVARIANT_SUPPORT" ,
237the
238.Fn lockmgr_assert
239function tests
240.Fa lkp
241for the assertions specified in
242.Fa what ,
243and panics if they are not met.
244One of the following assertions must be specified:
245.Bl -tag -width ".Dv KA_UNLOCKED"
246.It Dv KA_LOCKED
247Assert that the current thread has either a shared or an exclusive lock on the
248.Vt lkp
249lock pointed to by the first argument.
250.It Dv KA_SLOCKED
251Assert that the current thread has a shared lock on the
252.Vt lkp
253lock pointed to by the first argument.
254.It Dv KA_XLOCKED
255Assert that the current thread has an exclusive lock on the
256.Vt lkp
257lock pointed to by the first argument.
258.It Dv KA_UNLOCKED
259Assert that the current thread has no lock on the
260.Vt lkp
261lock pointed to by the first argument.
262.It Dv KA_HELD
263Assert that an unspecified thread has a lock on the
264.Vt lkp
265lock pointed to by the first argument.
266.It Dv KA_UNHELD
267Assert that no thread has a lock on the
268.Vt lkp
269lock pointed to by the first argument.
270.El
271.Pp
272In addition, one of the following optional assertions can be used with
273either an
274.Dv KA_LOCKED ,
275.Dv KA_SLOCKED ,
276or
277.Dv KA_XLOCKED
278assertion:
279.Bl -tag -width ".Dv KA_NOTRECURSED"
280.It Dv KA_RECURSED
281Assert that the current thread has a recursed lock on
282.Fa lkp .
283.It Dv KA_NOTRECURSED
284Assert that the current thread does not have a recursed lock on
285.Fa lkp .
286.El
287.Pp
288Note that
289.Dv KA_HELD
290and
291.Dv KA_UNHELD
292usage is highly discouraged.
293They are intended to cater a bad behaviour
294introduced by buffer cache lock handling.
295They will hopefully be
296made useless by revisiting such locks.
297.Sh RETURN VALUES
298The
299.Fn lockmgr
300function returns 0 on success and non-zero on failure.
301.Pp
302The
303.Fn lockstatus
304function returns:
305.Bl -tag -width ".Dv LK_EXCLUSIVE"
306.It Dv LK_EXCLUSIVE
307An exclusive lock is held by the current thread.
308.It Dv LK_EXCLOTHER
309An exclusive lock is held by someone other than the current thread.
310.It Dv LK_SHARED
311A shared lock is held.
312.It Li 0
313The lock is not held by anyone.
314.El
315.Sh ERRORS
316.Fn lockmgr
317fails if:
318.Bl -tag -width Er
319.It Bq Er EBUSY
320.Dv LK_FORCEUPGRADE
321was requested and another thread had already requested a lock upgrade.
322.It Bq Er EBUSY
323.Dv LK_NOWAIT
324was set, and a sleep would have been required.
325.It Bq Er ENOLCK
326.Dv LK_SLEEPFAIL
327was set and
328.Fn lockmgr
329did sleep.
330.It Bq Er EINTR
331.Dv PCATCH
332was set in the lock priority, and a signal was delivered during a sleep.
333Note the
334.Er ERESTART
335error below.
336.It Bq Er ERESTART
337.Dv PCATCH
338was set in the lock priority, a signal was delivered during a sleep,
339and the system call is to be restarted.
340.It Bq Er EWOULDBLOCK
341a non-zero timeout was given, and the timeout expired.
342.El
343.Sh LOCKS
344If
345.Dv LK_INTERLOCK
346is passed in the
347.Fa flags
348argument to
349.Fn lockmgr ,
350the
351.Fa interlkp
352must be held prior to calling
353.Fn lockmgr ,
354and will be returned unlocked.
355.Pp
356Upgrade attempts that fail result in the loss of the lock that
357is currently held.
358Also, it is invalid to upgrade an
359exclusive lock, and a
360.Xr panic 9
361will be the result of trying.
362.Sh SEE ALSO
363.Xr condvar 9 ,
364.Xr locking 9 ,
365.Xr mutex 9 ,
366.Xr rwlock 9 ,
367.Xr sleep 9 ,
368.Xr sx 9 ,
369.Xr mtx_assert 9 ,
370.Xr panic 9 ,
371.Xr VOP_PRINT 9
372.Sh AUTHORS
373This manual page was written by
374.An Chad David Aq davidc@acns.ab.ca .