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New diagnostic routine - mutex_ownable()
While working on getting the localcount(9) stuff whipped into shape, I
ran across a situation where it is desirable to ensure that the current
process/lwp does not already own a mutex.
We cannot use !mutex_owned() since that doesn't return the desired
result for a spin mutex, so I'm proposing to add a new routine called
mutex_ownable(). This does nothing in normal kernels, but for LOCKDEBUG
kernels it does a mutex_enter() followed immediately by mutex_exit().
If the current process already owns the mutex, the system will panic
with a "locking against myself" error; otherwise mutex_ownable() just
returns 1, enabling its use as
KASSERT(mutex_ownable(mtx));
Diffs are attached (including man-page and sets-list updates).
Comments? Any reason why this cannot be committed?
(Thanks to riastradh@ for the idea and initial review.)
+------------------+--------------------------+----------------------------+
| Paul Goyette | PGP Key fingerprint: | E-mail addresses: |
| (Retired) | FA29 0E3B 35AF E8AE 6651 | paul at whooppee dot com |
| Kernel Developer | 0786 F758 55DE 53BA 7731 | pgoyette at netbsd dot org |
+------------------+--------------------------+----------------------------+
Index: sys/mutex.h
===================================================================
RCS file: /cvsroot/src/sys/sys/mutex.h,v
retrieving revision 1.20
diff -u -p -r1.20 mutex.h
--- sys/mutex.h 8 Feb 2010 09:54:27 -0000 1.20
+++ sys/mutex.h 30 Apr 2017 00:38:44 -0000
@@ -204,6 +204,7 @@ void mutex_spin_exit(kmutex_t *);
int mutex_tryenter(kmutex_t *);
int mutex_owned(kmutex_t *);
+int mutex_ownable(kmutex_t *);
lwp_t *mutex_owner(kmutex_t *);
void mutex_obj_init(void);
Index: kern/kern_mutex.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_mutex.c,v
retrieving revision 1.64
diff -u -p -r1.64 kern_mutex.c
--- kern/kern_mutex.c 26 Jan 2017 04:11:56 -0000 1.64
+++ kern/kern_mutex.c 30 Apr 2017 00:38:44 -0000
@@ -831,6 +831,24 @@ mutex_owner(kmutex_t *mtx)
}
/*
+ * mutex_ownable:
+ *
+ * When compiled with LOCKDEBUG defined, ensure that the
+ * mutex is available. We cannot use !mutex_owned()
+ * since that won't work correctly for spin mutexes.
+ */
+int
+mutex_ownable(kmutex_t *mtx)
+{
+
+#ifdef LOCKDEBUG
+ mutex_enter(mtx);
+ mutex_exit(mtx);
+#endif
+ return 1;
+}
+
+/*
* mutex_tryenter:
*
* Try to acquire the mutex; return non-zero if we did.
Index: ../share/man/man9/Makefile
===================================================================
RCS file: /cvsroot/src/share/man/man9/Makefile,v
retrieving revision 1.409.2.2
diff -u -p -r1.409.2.2 Makefile
--- ../share/man/man9/Makefile 28 Apr 2017 06:00:33 -0000 1.409.2.2
+++ ../share/man/man9/Makefile 30 Apr 2017 00:38:44 -0000
@@ -516,6 +516,7 @@ MLINKS+=module.9 module_autoload.9 \
MLINKS+=mstohz.9 hztoms.9
MLINKS+=mutex.9 mutex_init.9 mutex.9 mutex_destroy.9 mutex.9 mutex_enter.9 \
mutex.9 mutex_exit.9 mutex.9 mutex_tryenter.9 mutex.9 mutex_owned.9 \
+ mutex.9 mutex_ownable.9 \
mutex.9 mutex_spin_enter.9 mutex.9 mutex_spin_exit.9
MLINKS+=m_tag.9 m_tag_copy.9 \
m_tag.9 m_tag_copy_chain.9 \
Index: ../share/man/man9/mutex.9
===================================================================
RCS file: /cvsroot/src/share/man/man9/mutex.9,v
retrieving revision 1.26
diff -u -p -r1.26 mutex.9
--- ../share/man/man9/mutex.9 4 Sep 2013 10:17:58 -0000 1.26
+++ ../share/man/man9/mutex.9 30 Apr 2017 00:38:44 -0000
@@ -36,6 +36,7 @@
.Nm mutex_destroy ,
.Nm mutex_enter ,
.Nm mutex_exit ,
+.Nm mutex_ownable ,
.Nm mutex_owned ,
.Nm mutex_spin_enter ,
.Nm mutex_spin_exit ,
@@ -52,6 +53,8 @@
.Ft void
.Fn mutex_exit "kmutex_t *mtx"
.Ft int
+.Fn mutex_ownable "kmutex_t *mtx"
+.Ft int
.Fn mutex_owned "kmutex_t *mtx"
.Ft void
.Fn mutex_spin_enter "kmutex_t *mtx"
@@ -172,6 +175,18 @@ if it is not already equal or higher.
Release a mutex.
The mutex must have been previously acquired by the caller.
Mutexes may be released out of order as needed.
+.It Fn mutex_ownable "mtx"
+.Pp
+When compiled with LOCKDEBUG (see
+.Xr options 4 ) ,
+ensure that the current process can successfully acquire mtx.
+If mtx is already owned by the current process, the system will panic
+with a "locking against myself" error.
+.Pp
+This function is needed because
+.Fn mutex_owned
+does not differentiate if a spin mutex is owned by the current process
+vs owned by another process.
.It Fn mutex_owned "mtx"
.Pp
For adaptive mutexes, return non-zero if the current LWP holds the mutex.
cvs diff: Diffing ../share/man/man9/man9.i386
cvs diff: Diffing ../share/man/man9/man9.sun3
cvs diff: Diffing ../share/man/man9/man9.x86
cvs diff: Diffing ../distrib/sets/lists/comp
Index: ../distrib/sets/lists/comp/mi
===================================================================
RCS file: /cvsroot/src/distrib/sets/lists/comp/mi,v
retrieving revision 1.2125.2.2
diff -u -p -r1.2125.2.2 mi
--- ../distrib/sets/lists/comp/mi 28 Apr 2017 06:00:33 -0000 1.2125.2.2
+++ ../distrib/sets/lists/comp/mi 30 Apr 2017 00:38:45 -0000
@@ -10836,6 +10836,7 @@
./usr/share/man/cat9/mutex_enter.0 comp-sys-catman .cat
./usr/share/man/cat9/mutex_exit.0 comp-sys-catman .cat
./usr/share/man/cat9/mutex_init.0 comp-sys-catman .cat
+./usr/share/man/cat9/mutex_ownable.0 comp-sys-catman .cat
./usr/share/man/cat9/mutex_owned.0 comp-sys-catman .cat
./usr/share/man/cat9/mutex_spin_enter.0 comp-sys-catman .cat
./usr/share/man/cat9/mutex_spin_exit.0 comp-sys-catman .cat
@@ -18278,6 +18279,7 @@
./usr/share/man/html9/mutex_enter.html comp-sys-htmlman html
./usr/share/man/html9/mutex_exit.html comp-sys-htmlman html
./usr/share/man/html9/mutex_init.html comp-sys-htmlman html
+./usr/share/man/html9/mutex_ownable.html comp-sys-htmlman html
./usr/share/man/html9/mutex_owned.html comp-sys-htmlman html
./usr/share/man/html9/mutex_spin_enter.html comp-sys-htmlman html
./usr/share/man/html9/mutex_spin_exit.html comp-sys-htmlman html
@@ -25876,6 +25878,7 @@
./usr/share/man/man9/mutex_enter.9 comp-sys-man .man
./usr/share/man/man9/mutex_exit.9 comp-sys-man .man
./usr/share/man/man9/mutex_init.9 comp-sys-man .man
+./usr/share/man/man9/mutex_ownable.9 comp-sys-man .man
./usr/share/man/man9/mutex_owned.9 comp-sys-man .man
./usr/share/man/man9/mutex_spin_enter.9 comp-sys-man .man
./usr/share/man/man9/mutex_spin_exit.9 comp-sys-man .man
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