Module Name: src
Committed By: ad
Date: Sat Feb 22 21:24:45 UTC 2020
Modified Files:
src/distrib/sets/lists/comp: mi
src/share/man/man9: rwlock.9
src/sys/kern: kern_rwlock.c
src/sys/sys: rwlock.h
Log Message:
Add rw_lock_op(): return either RW_READER or RW_WRITER for a lock that is
known to be held by the caller. Panic if the lock is not held.
To generate a diff of this commit:
cvs rdiff -u -r1.2310 -r1.2311 src/distrib/sets/lists/comp/mi
cvs rdiff -u -r1.19 -r1.20 src/share/man/man9/rwlock.9
cvs rdiff -u -r1.64 -r1.65 src/sys/kern/kern_rwlock.c
cvs rdiff -u -r1.15 -r1.16 src/sys/sys/rwlock.h
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/distrib/sets/lists/comp/mi
diff -u src/distrib/sets/lists/comp/mi:1.2310 src/distrib/sets/lists/comp/mi:1.2311
--- src/distrib/sets/lists/comp/mi:1.2310 Fri Feb 7 18:48:58 2020
+++ src/distrib/sets/lists/comp/mi Sat Feb 22 21:24:44 2020
@@ -1,4 +1,4 @@
-# $NetBSD: mi,v 1.2310 2020/02/07 18:48:58 kamil Exp $
+# $NetBSD: mi,v 1.2311 2020/02/22 21:24:44 ad Exp $
#
# Note: don't delete entries from here - mark them as "obsolete" instead.
./etc/mtree/set.comp comp-sys-root
@@ -11792,6 +11792,7 @@
./usr/share/man/cat9/rw_exit.0 comp-sys-catman .cat
./usr/share/man/cat9/rw_init.0 comp-sys-catman .cat
./usr/share/man/cat9/rw_lock_held.0 comp-sys-catman .cat
+./usr/share/man/cat9/rw_lock_op.0 comp-sys-catman .cat
./usr/share/man/cat9/rw_read_held.0 comp-sys-catman .cat
./usr/share/man/cat9/rw_tryenter.0 comp-sys-catman .cat
./usr/share/man/cat9/rw_tryupgrade.0 comp-sys-catman .cat
@@ -19710,6 +19711,7 @@
./usr/share/man/html9/rw_exit.html comp-sys-htmlman html
./usr/share/man/html9/rw_init.html comp-sys-htmlman html
./usr/share/man/html9/rw_lock_held.html comp-sys-htmlman html
+./usr/share/man/html9/rw_lock_op.html comp-sys-htmlman html
./usr/share/man/html9/rw_read_held.html comp-sys-htmlman html
./usr/share/man/html9/rw_tryenter.html comp-sys-htmlman html
./usr/share/man/html9/rw_tryupgrade.html comp-sys-htmlman html
@@ -27811,6 +27813,7 @@
./usr/share/man/man9/rw_exit.9 comp-sys-man .man
./usr/share/man/man9/rw_init.9 comp-sys-man .man
./usr/share/man/man9/rw_lock_held.9 comp-sys-man .man
+./usr/share/man/man9/rw_lock_op.9 comp-sys-man .man
./usr/share/man/man9/rw_read_held.9 comp-sys-man .man
./usr/share/man/man9/rw_tryenter.9 comp-sys-man .man
./usr/share/man/man9/rw_tryupgrade.9 comp-sys-man .man
Index: src/share/man/man9/rwlock.9
diff -u src/share/man/man9/rwlock.9:1.19 src/share/man/man9/rwlock.9:1.20
--- src/share/man/man9/rwlock.9:1.19 Mon Dec 10 20:12:36 2018
+++ src/share/man/man9/rwlock.9 Sat Feb 22 21:24:45 2020
@@ -1,6 +1,6 @@
-.\" $NetBSD: rwlock.9,v 1.19 2018/12/10 20:12:36 jdolecek Exp $
+.\" $NetBSD: rwlock.9,v 1.20 2020/02/22 21:24:45 ad Exp $
.\"
-.\" Copyright (c) 2006, 2007, 2009 The NetBSD Foundation, Inc.
+.\" Copyright (c) 2006, 2007, 2009, 2020 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
@@ -27,7 +27,7 @@
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
-.Dd December 10, 2018
+.Dd February 22, 2020
.Dt RWLOCK 9
.Os
.Sh NAME
@@ -41,7 +41,8 @@
.Nm rw_downgrade ,
.Nm rw_read_held ,
.Nm rw_write_held ,
-.Nm rw_lock_held
+.Nm rw_lock_held ,
+.Nm rw_lock_op
.Nd reader / writer lock primitives
.Sh SYNOPSIS
.In sys/rwlock.h
@@ -65,6 +66,8 @@
.Fn rw_write_held "krwlock_t *rw"
.Ft int
.Fn rw_lock_held "krwlock_t *rw"
+.Ft krw_t
+.Fn rw_lock_op "krwlock_t *rw"
.Pp
.Cd "options DIAGNOSTIC"
.Cd "options LOCKDEBUG"
@@ -130,8 +133,7 @@ If
is specified as the argument to
.Fa op ,
acquire a read lock.
-If the lock is write held, the caller will block and not return until the
-hold is acquired.
+The caller may block and will not return until the hold is acquired.
Callers must not recursively acquire read locks.
.Pp
If
@@ -172,6 +174,7 @@ Downgrade a lock from a write hold to a
Return non-zero if write lock is held by current lwp.
Otherwise, return zero.
.It Fn rw_read_held "rw"
+.Pp
Returns non-zero if read lock is held by any lwp.
Otherwise, return zero.
.It Fn rw_lock_held "rw"
@@ -179,19 +182,28 @@ Otherwise, return zero.
Returns non-zero if either read or write lock is held by any lwp.
Otherwise, return zero.
.Pp
-Functions
.Fn rw_write_held ,
.Fn rw_read_held ,
and
.Fn rw_lock_held
-must never be used to make locking decisions at run time:
-they are provided only for diagnostic purposes.
-They are also not atomic, hence they should only be used to assert
-that lock is held.
-The only exception is
+should not generally be used to make locking decisions at run time:
+they are provided for diagnostic purposes, for example making
+assertions.
+.Pp
+Negative assertions (lock not held) should not be made due to atomicity
+issues, excepting
.Fn rw_write_held ,
-which can be also used safely to assert that write lock is NOT currently
-held by current lwp.
+which can safely be used to assert that a write lock is NOT held by
+the current LWP.
+.It Fn rw_lock_op "rw"
+.Pp
+For a lock that is known to be held by the calling LWP, return either
+.Dv RW_READER
+or
+.Dv RW_WRITER
+to denote the type of hold.
+This is useful when dropping and later re-acquiring a lock, if the type
+of hold is not already known.
.El
.Sh PERFORMANCE CONSIDERATIONS
RW locks are subject to high cache contention on multiprocessor systems,
Index: src/sys/kern/kern_rwlock.c
diff -u src/sys/kern/kern_rwlock.c:1.64 src/sys/kern/kern_rwlock.c:1.65
--- src/sys/kern/kern_rwlock.c:1.64 Wed Jan 22 12:44:54 2020
+++ src/sys/kern/kern_rwlock.c Sat Feb 22 21:24:45 2020
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_rwlock.c,v 1.64 2020/01/22 12:44:54 ad Exp $ */
+/* $NetBSD: kern_rwlock.c,v 1.65 2020/02/22 21:24:45 ad Exp $ */
/*-
* Copyright (c) 2002, 2006, 2007, 2008, 2009, 2019, 2020
@@ -45,7 +45,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_rwlock.c,v 1.64 2020/01/22 12:44:54 ad Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_rwlock.c,v 1.65 2020/02/22 21:24:45 ad Exp $");
#include "opt_lockdebug.h"
@@ -782,6 +782,21 @@ rw_lock_held(krwlock_t *rw)
}
/*
+ * rw_lock_op:
+ *
+ * For a rwlock that is known to be held by the caller, return
+ * RW_READER or RW_WRITER to describe the hold type.
+ */
+krw_t
+rw_lock_op(krwlock_t *rw)
+{
+
+ RW_ASSERT(rw, rw_lock_held(rw));
+
+ return (rw->rw_owner & RW_WRITE_LOCKED) != 0 ? RW_WRITER : RW_READER;
+}
+
+/*
* rw_owner:
*
* Return the current owner of an RW lock, but only if it is write
Index: src/sys/sys/rwlock.h
diff -u src/sys/sys/rwlock.h:1.15 src/sys/sys/rwlock.h:1.16
--- src/sys/sys/rwlock.h:1.15 Tue Jan 21 20:29:51 2020
+++ src/sys/sys/rwlock.h Sat Feb 22 21:24:45 2020
@@ -1,4 +1,4 @@
-/* $NetBSD: rwlock.h,v 1.15 2020/01/21 20:29:51 ad Exp $ */
+/* $NetBSD: rwlock.h,v 1.16 2020/02/22 21:24:45 ad Exp $ */
/*-
* Copyright (c) 2002, 2006, 2007, 2008, 2019, 2020 The NetBSD Foundation, Inc.
@@ -103,6 +103,7 @@ void rw_downgrade(krwlock_t *);
int rw_read_held(krwlock_t *);
int rw_write_held(krwlock_t *);
int rw_lock_held(krwlock_t *);
+krw_t rw_lock_op(krwlock_t *);
void rw_enter(krwlock_t *, const krw_t);
void rw_exit(krwlock_t *);
