Pull up following revision(s) (requested by ozaki-r in ticket #687):
sys/kern/kern_rwlock_obj.c: revision 1.4
sys/rump/librump/rumpkern/locks.c: revision 1.80
sys/kern/kern_rwlock.c: revision 1.50
sys/arch/x86/x86/db_memrw.c: revision 1.5,1.6
sys/ddb/db_command.c: revision 1.150-1.153
share/man/man4/ddb.4: revision 1.175 (via patch),1.176-1.178
sys/kern/kern_mutex_obj.c: revision 1.6
sys/kern/subr_lockdebug.c: revision 1.61-1.64
sys/sys/lockdebug.h: revision 1.17
sys/kern/kern_mutex.c: revision 1.71
sys/sys/lockdebug.h: revision 1.18,1.19
sys/kern/subr_xcall.c: revision 1.26

Obtain proper initialized addresses of locks allocated by mutex_obj_alloc or rw_obj_alloc

Initialized addresses of locks allocated by mutex_obj_alloc or rw_obj_alloc
were not useful because the addresses were mutex_obj_alloc or rw_obj_alloc
itself. What we want to know are callers of them.

Spinkle ASSERT_SLEEPABLE to xcall functions

Use db_printf instead of printf in ddb

Add a new command, show lockstat, which shows statistics of locks
Currently the command shows the number of allocated locks.
The command is useful only if LOCKDEBUG is enabled.

Add a new command, show all locks, which shows information of active locks

The command shows information of all active (i.e., being held) locks that are
tracked through either of LWPs or CPUs by the LOCKDEBUG facility.  The /t
modifier additionally shows a backtrace for each LWP additionally.  This
feature is useful for debugging especially to analyze deadlocks.
The command is useful only if LOCKDEBUG is enabled.

Don't pass a unset address to lockdebug_lock_print

x86: avoid accessing invalid addresses in ddb like arm32
This avoids that a command stops in the middle of an execution if
a fault occurs due to an access to an invalid address.

Get rid of a redundant output

Improve wording. Fix a Cm argument.

ddb: rename "show lockstat" to "show lockstats" to avoid conflicting with lockstat(8)
Requested by mrg@

(martin)