Index: head/share/man/man9/rmlock.9 =================================================================== --- head/share/man/man9/rmlock.9 (revision 275812) +++ head/share/man/man9/rmlock.9 (revision 275813) @@ -1,323 +1,323 @@ .\" Copyright (c) 2007 Stephan Uphoff .\" Copyright (c) 2006 Gleb Smirnoff .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" $FreeBSD$ .\" .\" Based on rwlock.9 man page .Dd December 13, 2014 .Dt RMLOCK 9 .Os .Sh NAME .Nm rmlock , .Nm rm_init , .Nm rm_init_flags , .Nm rm_destroy , .Nm rm_rlock , .Nm rm_try_rlock , .Nm rm_wlock , .Nm rm_runlock , .Nm rm_wunlock , .Nm rm_wowned , .Nm rm_sleep , .Nm rm_assert , .Nm RM_SYSINIT .Nd kernel reader/writer lock optimized for read-mostly access patterns .Sh SYNOPSIS .In sys/param.h .In sys/lock.h .In sys/rmlock.h .Ft void .Fn rm_init "struct rmlock *rm" "const char *name" .Ft void .Fn rm_init_flags "struct rmlock *rm" "const char *name" "int opts" .Ft void .Fn rm_destroy "struct rmlock *rm" .Ft void .Fn rm_rlock "struct rmlock *rm" "struct rm_priotracker* tracker" .Ft int .Fn rm_try_rlock "struct rmlock *rm" "struct rm_priotracker* tracker" .Ft void .Fn rm_wlock "struct rmlock *rm" .Ft void .Fn rm_runlock "struct rmlock *rm" "struct rm_priotracker* tracker" .Ft void .Fn rm_wunlock "struct rmlock *rm" .Ft int .Fn rm_wowned "const struct rmlock *rm" .Ft int .Fn rm_sleep "void *wchan" "struct rmlock *rm" "int priority" "const char *wmesg" "int timo" .Pp .Cd "options INVARIANTS" .Cd "options INVARIANT_SUPPORT" .Ft void .Fn rm_assert "struct rmlock *rm" "int what" .In sys/kernel.h .Fn RM_SYSINIT "name" "struct rmlock *rm" "const char *desc" "int opts" .Sh DESCRIPTION Read-mostly locks allow shared access to protected data by multiple threads, or exclusive access by a single thread. The threads with shared access are known as .Em readers since they only read the protected data. A thread with exclusive access is known as a .Em writer since it can modify protected data. .Pp Read-mostly locks are designed to be efficient for locks almost exclusively used as reader locks and as such should be used for protecting data that rarely changes. Acquiring an exclusive lock after the lock has been locked for shared access is an expensive operation. .Pp Normal read-mostly locks are similar to .Xr rwlock 9 locks and follow the same lock ordering rules as .Xr rwlock 9 locks. Read-mostly locks have full priority propagation like mutexes. Unlike .Xr rwlock 9 , read-mostly locks propagate priority to both readers and writers. This is implemented via the .Va rm_priotracker structure argument supplied to .Fn rm_rlock and .Fn rm_runlock . Readers can recurse if the lock is initialized with the .Dv RM_RECURSE option; however, writers are never allowed to recurse. .Pp Sleepable read-mostly locks are created by passing .Dv RM_SLEEPABLE to .Fn rm_init_flags . Unlike normal read-mostly locks, sleepable read-mostly locks follow the same lock ordering rules as .Xr sx 9 locks. Sleepable read-mostly locks do not propagate priority to writers, but they do propagate priority to readers. Writers are permitted to sleep while holding a read-mostly lock, but readers are not. Unlike other sleepable locks such as .Xr sx 9 locks, readers must use try operations on other sleepable locks to avoid sleeping. .Ss Macros and Functions .Bl -tag -width indent .It Fn rm_init "struct rmlock *rm" "const char *name" Initialize the read-mostly lock .Fa rm . The .Fa name description is used solely for debugging purposes. This function must be called before any other operations on the lock. .It Fn rm_init_flags "struct rmlock *rm" "const char *name" "int opts" Similar to .Fn rm_init , initialize the read-mostly lock .Fa rm with a set of optional flags. The .Fa opts arguments contains one or more of the following flags: .Bl -tag -width ".Dv RM_NOWITNESS" .It Dv RM_NOWITNESS Instruct .Xr witness 4 to ignore this lock. .It Dv RM_RECURSE Allow threads to recursively acquire shared locks for .Fa rm . .It Dv RM_SLEEPABLE Create a sleepable read-mostly lock. .It Dv RM_NEW If the kernel has been compiled with .Cd "option INVARIANTS" , .Fn rm_init_flags will assert that the .Fa rm has not been initialized multiple times without intervening calls to .Fn rm_destroy unless this option is specified. .El .It Fn rm_rlock "struct rmlock *rm" "struct rm_priotracker* tracker" Lock .Fa rm as a reader using .Fa tracker to track read owners of a lock for priority propagation. This data structure is only used internally by .Nm and must persist until .Fn rm_runlock has been called. This data structure can be allocated on the stack since readers cannot sleep. If any thread holds this lock exclusively, the current thread blocks, and its priority is propagated to the exclusive holder. If the lock was initialized with the .Dv RM_RECURSE option the .Fn rm_rlock function can be called when the current thread has already acquired reader access on .Fa rm . .It Fn rm_try_rlock "struct rmlock *rm" "struct rm_priotracker* tracker" Try to lock .Fa rm as a reader. .Fn rm_try_rlock will return 0 if the lock cannot be acquired immediately; otherwise, the lock will be acquired and a non-zero value will be returned. Note that .Fn rm_try_rlock may fail even while the lock is not currently held by a writer. If the lock was initialized with the .Dv RM_RECURSE option, .Fn rm_try_rlock will succeed if the current thread has already acquired reader access. .It Fn rm_wlock "struct rmlock *rm" Lock .Fa rm as a writer. If there are any shared owners of the lock, the current thread blocks. The .Fn rm_wlock function cannot be called recursively. .It Fn rm_runlock "struct rmlock *rm" "struct rm_priotracker* tracker" This function releases a shared lock previously acquired by .Fn rm_rlock . The .Fa tracker argument must match the .Fa tracker argument used for acquiring the shared lock .It Fn rm_wunlock "struct rmlock *rm" This function releases an exclusive lock previously acquired by .Fn rm_wlock . .It Fn rm_destroy "struct rmlock *rm" This functions destroys a lock previously initialized with .Fn rm_init . The .Fa rm lock must be unlocked. .It Fn rm_wowned "const struct rmlock *rm" This function returns a non-zero value if the current thread owns an exclusive lock on .Fa rm . .It Fn rm_sleep "void *wchan" "struct rmlock *rm" "int priority" "const char *wmesg" "int timo" This function atomically releases .Fa rm while waiting for an event. The .Fa rm lock must be exclusively locked. For more details on the parameters to this function, see .Xr sleep 9 . .It Fn rm_assert "struct rmlock *rm" "int what" This function asserts that the .Fa rm lock is in the state specified by .Fa what . If the assertions are not true and the kernel is compiled with .Cd "options INVARIANTS" and .Cd "options INVARIANT_SUPPORT" , the kernel will panic. Currently the following base assertions are supported: .Bl -tag -width ".Dv RA_UNLOCKED" .It Dv RA_LOCKED Assert that current thread holds either a shared or exclusive lock of .Fa rm . .It Dv RA_RLOCKED Assert that current thread holds a shared lock of .Fa rm . .It Dv RA_WLOCKED Assert that current thread holds an exclusive lock of .Fa rm . .It Dv RA_UNLOCKED Assert that current thread holds neither a shared nor exclusive lock of .Fa rm . .El .Pp In addition, one of the following optional flags may be specified with .Dv RA_LOCKED , .Dv RA_RLOCKED , or .Dv RA_WLOCKED : .Bl -tag -width ".Dv RA_NOTRECURSED" .It Dv RA_RECURSED Assert that the current thread holds a recursive lock of .Fa rm . .It Dv RA_NOTRECURSED Assert that the current thread does not hold a recursive lock of .Fa rm . .El .El .Sh SEE ALSO .Xr locking 9 , .Xr mutex 9 , .Xr panic 9 , .Xr rwlock 9 , -.Xr sleep 9 , .Xr sema 9 , +.Xr sleep 9 , .Xr sx 9 .Sh HISTORY These functions appeared in .Fx 7.0 . .Sh AUTHORS .An -nosplit The .Nm facility was written by .An "Stephan Uphoff" . This manual page was written by .An "Gleb Smirnoff" for rwlock and modified to reflect rmlock by .An "Stephan Uphoff" . .Sh BUGS The .Nm implementation is currently not optimized for single processor systems. .Pp .Fn rm_try_rlock can fail transiently even when there is no writer, while another reader updates the state on the local CPU. .Pp The .Nm implementation uses a single per CPU list shared by all rmlocks in the system. If rmlocks become popular, hashing to multiple per CPU queues may be needed to speed up the writer lock process. Index: head/share/man/man9/sx.9 =================================================================== --- head/share/man/man9/sx.9 (revision 275812) +++ head/share/man/man9/sx.9 (revision 275813) @@ -1,337 +1,337 @@ .\" .\" Copyright (C) 2001 Jason Evans . All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice(s), this list of conditions and the following disclaimer as .\" the first lines of this file unmodified other than the possible .\" addition of one or more copyright notices. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice(s), this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" .\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY .\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED .\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE .\" DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY .\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES .\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR .\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER .\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH .\" DAMAGE. .\" .\" $FreeBSD$ .\" .Dd December 13, 2014 .Dt SX 9 .Os .Sh NAME .Nm sx , .Nm sx_init , .Nm sx_init_flags , .Nm sx_destroy , .Nm sx_slock , .Nm sx_xlock , .Nm sx_slock_sig , .Nm sx_xlock_sig , .Nm sx_try_slock , .Nm sx_try_xlock , .Nm sx_sunlock , .Nm sx_xunlock , .Nm sx_unlock , .Nm sx_try_upgrade , .Nm sx_downgrade , .Nm sx_sleep , .Nm sx_xholder , .Nm sx_xlocked , .Nm sx_assert , .Nm SX_SYSINIT .Nd kernel shared/exclusive lock .Sh SYNOPSIS .In sys/param.h .In sys/lock.h .In sys/sx.h .Ft void .Fn sx_init "struct sx *sx" "const char *description" .Ft void .Fn sx_init_flags "struct sx *sx" "const char *description" "int opts" .Ft void .Fn sx_destroy "struct sx *sx" .Ft void .Fn sx_slock "struct sx *sx" .Ft void .Fn sx_xlock "struct sx *sx" .Ft int .Fn sx_slock_sig "struct sx *sx" .Ft int .Fn sx_xlock_sig "struct sx *sx" .Ft int .Fn sx_try_slock "struct sx *sx" .Ft int .Fn sx_try_xlock "struct sx *sx" .Ft void .Fn sx_sunlock "struct sx *sx" .Ft void .Fn sx_xunlock "struct sx *sx" .Ft void .Fn sx_unlock "struct sx *sx" .Ft int .Fn sx_try_upgrade "struct sx *sx" .Ft void .Fn sx_downgrade "struct sx *sx" .Ft int .Fn sx_sleep "void *chan" "struct sx *sx" "int priority" "const char *wmesg" "int timo" .Ft "struct thread *" .Fn sx_xholder "struct sx *sx" .Ft int .Fn sx_xlocked "const struct sx *sx" .Pp .Cd "options INVARIANTS" .Cd "options INVARIANT_SUPPORT" .Ft void .Fn sx_assert "const struct sx *sx" "int what" .In sys/kernel.h .Fn SX_SYSINIT "name" "struct sx *sx" "const char *description" .Sh DESCRIPTION Shared/exclusive locks are used to protect data that are read far more often than they are written. Shared/exclusive locks do not implement priority propagation like mutexes and reader/writer locks to prevent priority inversions, so shared/exclusive locks should be used prudently. .Pp Shared/exclusive locks are created with either .Fn sx_init or .Fn sx_init_flags where .Fa sx is a pointer to space for a .Vt struct sx , and .Fa description is a pointer to a null-terminated character string that describes the shared/exclusive lock. The .Fa opts argument to .Fn sx_init_flags specifies a set of optional flags to alter the behavior of .Fa sx . It contains one or more of the following flags: .Bl -tag -width SX_NOADAPTIVE .It Dv SX_NOADAPTIVE If the kernel is not compiled with .Cd "options NO_ADAPTIVE_SX" , then lock operations for .Fa sx will spin instead of sleeping while an exclusive lock holder is executing on another CPU. .It Dv SX_DUPOK Witness should not log messages about duplicate locks being acquired. .It Dv SX_NOWITNESS Instruct .Xr witness 4 to ignore this lock. .It Dv SX_NOPROFILE Do not profile this lock. .It Dv SX_RECURSE Allow threads to recursively acquire exclusive locks for .Fa sx . .It Dv SX_QUIET Do not log any operations for this lock via .Xr ktr 4 . .It Dv SX_NEW If the kernel has been compiled with .Cd "options INVARIANTS" , .Fn sx_init will assert that the .Fa sx has not been initialized multiple times without intervening calls to .Fn sx_destroy unless this option is specified. .El .Pp Shared/exclusive locks are destroyed with .Fn sx_destroy . The lock .Fa sx must not be locked by any thread when it is destroyed. .Pp Threads acquire and release a shared lock by calling .Fn sx_slock , .Fn sx_slock_sig or .Fn sx_try_slock and .Fn sx_sunlock or .Fn sx_unlock . Threads acquire and release an exclusive lock by calling .Fn sx_xlock , .Fn sx_xlock_sig or .Fn sx_try_xlock and .Fn sx_xunlock or .Fn sx_unlock . A thread can attempt to upgrade a currently held shared lock to an exclusive lock by calling .Fn sx_try_upgrade . A thread that has an exclusive lock can downgrade it to a shared lock by calling .Fn sx_downgrade . .Pp .Fn sx_try_slock and .Fn sx_try_xlock will return 0 if the shared/exclusive lock cannot be acquired immediately; otherwise the shared/exclusive lock will be acquired and a non-zero value will be returned. .Pp .Fn sx_try_upgrade will return 0 if the shared lock cannot be upgraded to an exclusive lock immediately; otherwise the exclusive lock will be acquired and a non-zero value will be returned. .Pp .Fn sx_slock_sig and .Fn sx_xlock_sig do the same as their normal versions but performing an interruptible sleep. They return a non-zero value if the sleep has been interrupted by a signal or an interrupt, otherwise 0. .Pp A thread can atomically release a shared/exclusive lock while waiting for an event by calling .Fn sx_sleep . For more details on the parameters to this function, see .Xr sleep 9 . .Pp When compiled with .Cd "options INVARIANTS" and .Cd "options INVARIANT_SUPPORT" , the .Fn sx_assert function tests .Fa sx for the assertions specified in .Fa what , and panics if they are not met. One of the following assertions must be specified: .Bl -tag -width ".Dv SA_UNLOCKED" .It Dv SA_LOCKED Assert that the current thread has either a shared or an exclusive lock on the .Vt sx lock pointed to by the first argument. .It Dv SA_SLOCKED Assert that the current thread has a shared lock on the .Vt sx lock pointed to by the first argument. .It Dv SA_XLOCKED Assert that the current thread has an exclusive lock on the .Vt sx lock pointed to by the first argument. .It Dv SA_UNLOCKED Assert that the current thread has no lock on the .Vt sx lock pointed to by the first argument. .El .Pp In addition, one of the following optional assertions may be included with either an .Dv SA_LOCKED , .Dv SA_SLOCKED , or .Dv SA_XLOCKED assertion: .Bl -tag -width ".Dv SA_NOTRECURSED" .It Dv SA_RECURSED Assert that the current thread has a recursed lock on .Fa sx . .It Dv SA_NOTRECURSED Assert that the current thread does not have a recursed lock on .Fa sx . .El .Pp .Fn sx_xholder will return a pointer to the thread which currently holds an exclusive lock on .Fa sx . If no thread holds an exclusive lock on .Fa sx , then .Dv NULL is returned instead. .Pp .Fn sx_xlocked will return non-zero if the current thread holds the exclusive lock; otherwise, it will return zero. .Pp For ease of programming, .Fn sx_unlock is provided as a macro frontend to the respective functions, .Fn sx_sunlock and .Fn sx_xunlock . Algorithms that are aware of what state the lock is in should use either of the two specific functions for a minor performance benefit. .Pp The .Fn SX_SYSINIT macro is used to generate a call to the .Fn sx_sysinit routine at system startup in order to initialize a given .Fa sx lock. The parameters are the same as .Fn sx_init but with an additional argument, .Fa name , that is used in generating unique variable names for the related structures associated with the lock and the sysinit routine. .Pp A thread may not hold both a shared lock and an exclusive lock on the same lock simultaneously; attempting to do so will result in deadlock. .Sh CONTEXT A thread may hold a shared or exclusive lock on an .Nm lock while sleeping. As a result, an .Nm lock may not be acquired while holding a mutex. Otherwise, if one thread slept while holding an .Nm lock while another thread blocked on the same .Nm lock after acquiring a mutex, then the second thread would effectively end up sleeping while holding a mutex, which is not allowed. .Sh SEE ALSO -.Xr locking 9 , .Xr lock 9 , +.Xr locking 9 , .Xr mutex 9 , .Xr panic 9 , .Xr rwlock 9 , .Xr sema 9 .Sh BUGS Currently there is no way to assert that a lock is not held. This is not possible in the .No non- Ns Dv WITNESS case for asserting that this thread does not hold a shared lock. In the .No non- Ns Dv WITNESS case, the .Dv SA_LOCKED and .Dv SA_SLOCKED assertions merely check that some thread holds a shared lock. They do not ensure that the current thread holds a shared lock.