Commit Graph

52 Commits

Author SHA1 Message Date
Bjoern A. Zeeb
2430ab4629 Print the pointer to the lock with the panic message. The previous
panic: rw lock not unlocked
was not really helpful for debugging. Now one can at least call
	show lock <ptr>
form ddb to learn more about the lock.

MFC after:	3 days
2010-03-24 19:21:26 +00:00
Attilio Rao
ddce63ca73 When releasing a read/shared lock we need to use a write memory barrier
in order to avoid, on architectures which doesn't have strong ordered
writes, CPU instructions reordering.

Diagnosed by:	fabio
Reviewed by:	jhb
Tested by:	Giovanni Trematerra
		<giovanni dot trematerra at gmail dot com>
2009-09-30 13:26:31 +00:00
Attilio Rao
353998acc3 * Change the scope of the ASSERT_ATOMIC_LOAD() from a generic check to
a pointer-fetching specific operation check. Consequently, rename the
  operation ASSERT_ATOMIC_LOAD_PTR().
* Fix the implementation of ASSERT_ATOMIC_LOAD_PTR() by checking
  directly alignment on the word boundry, for all the given specific
  architectures. That's a bit too strict for some common case, but it
  assures safety.
* Add a comment explaining the scope of the macro
* Add a new stub in the lockmgr specific implementation

Tested by: marcel (initial version), marius
Reviewed by: rwatson, jhb (comment specific review)
Approved by: re (kib)
2009-08-17 16:17:21 +00:00
Bjoern A. Zeeb
8d518523cc Add a new macro to test that a variable could be loaded atomically.
Check that the given variable is at most uintptr_t in size and that
it is aligned.

Note: ASSERT_ATOMIC_LOAD() uses ALIGN() to check for adequate
      alignment -- however, the function of ALIGN() is to guarantee
      alignment, and therefore may lead to stronger alignment
      enforcement than necessary for types that are smaller than
      sizeof(uintptr_t).

Add checks to mtx, rw and sx locks init functions to detect possible
breakage. This was used during debugging of the problem fixed with
r196118 where a pointer was on an un-aligned address in the dpcpu area.

In collaboration with:	rwatson
Reviewed by:		rwatson
Approved by:		re (kib)
2009-08-14 21:46:54 +00:00
Attilio Rao
f083018223 Handle lock recursion differenty by always checking against LO_RECURSABLE
instead the lock own flag itself.

Tested by:	pho
2009-06-02 13:03:35 +00:00
John Baldwin
a571ad41ae Remove extra cpu_spinwait() invocations. This should really only be used
in tight spin loops, not in these edge cases where we restart a much
larger loop only a few times.

Reviewed by:	attilio
2009-05-29 14:03:34 +00:00
John Baldwin
fa29f0236f Tweak a few comments on adaptive spinning. 2009-05-29 13:56:34 +00:00
Stacey Son
a5aedd68b4 Add the OpenSolaris dtrace lockstat provider. The lockstat provider
adds probes for mutexes, reader/writer and shared/exclusive locks to
gather contention statistics and other locking information for
dtrace scripts, the lockstat(1M) command and other potential
consumers.

Reviewed by:	attilio jhb jb
Approved by:	gnn (mentor)
2009-05-26 20:28:22 +00:00
Jeff Roberson
1723a06485 - Wrap lock profiling state variables in #ifdef LOCK_PROFILING blocks. 2009-03-15 08:03:54 +00:00
Ed Schouten
c90c9021e9 Remove even more unneeded variable assignments.
kern_time.c:
- Unused variable `p'.

kern_thr.c:
- Variable `error' is always caught immediately, so no reason to
  initialize it. There is no way that error != 0 at the end of
  create_thread().

kern_sig.c:
- Unused variable `code'.

kern_synch.c:
- `rval' is always assigned in all different cases.

kern_rwlock.c:
- `v' is always overwritten with RW_UNLOCKED further on.

kern_malloc.c:
- `size' is always initialized with the proper value before being used.

kern_exit.c:
- `error' is always caught and returned immediately. abort2() never
  returns a non-zero value.

kern_exec.c:
- `len' is always assigned inside the if-statement right below it.

tty_info.c:
- `td' is always overwritten by FOREACH_THREAD_IN_PROC().

Found by:	LLVM's scan-build
2009-02-26 15:51:54 +00:00
Kip Macy
e1d881ba31 add RW_SYSINIT_FLAGS macro and rw_sysinit_flags initialization function 2008-12-08 21:46:55 +00:00
John Baldwin
413134305e Teach WITNESS about the interlocks used with lockmgr. This removes a bunch
of spurious witness warnings since lockmgr grew witness support.  Before
this, every time you passed an interlock to a lockmgr lock WITNESS treated
it as a LOR.

Reviewed by:	attilio
2008-09-10 19:13:30 +00:00
John Baldwin
bf9c6c31e7 Various whitespace fixes. 2008-09-10 17:59:21 +00:00
Attilio Rao
48972152ee Improve a comment which, in the actual CVS stock, doesn't completely
explain the logic of the code chunk.
2008-05-27 00:27:50 +00:00
Jeff Roberson
00ca09449d - Add sysctls at debug.rwlock to control the behavior of the speculative
spinning when readers hold a lock.  This spinning is speculative because,
   unlike the write case, we can not test whether the owners are running.
 - Add speculative read spinning for readers who are blocked by pending
   writers while a read lock is still held.  This allows the thread to
   spin until the write lock succeeds after which it may spin until the
   writer has released the lock.  This prevents excessive context switches
   when readers and writers both hold the lock for brief periods.

Sponsored by:	Nokia
2008-04-04 10:00:46 +00:00
Attilio Rao
b31a149bbb Add rw_try_rlock() and rw_try_wlock() to rwlocks.
These functions try the specified operation (rlocking and wlocking) and
true is returned if the operation completes, false otherwise.

The KPI is enriched by this commit, so __FreeBSD_version bumping and
manpage updating will happen soon.

Requested by:	jeff, kris
2008-04-01 20:31:55 +00:00
Jeff Roberson
0fef2c50b1 - In rw_wunlock_hard prefer to wakeup writers if there are both readers
and writers available.  Doing otherwise can cause deadlocks as no
   read locks can proceed while there are write waiters.

Sponsored by:	Nokia
2008-02-07 06:16:54 +00:00
Jeff Roberson
5dff04c31f Adaptive spinning in write path with readers and writer starvation avoidance.
- Move recursion checking into rwlock inlines to free a bit for use with
   adaptive spinners.
 - Clear the RW_LOCK_WRITE_SPINNERS flag whenever the lock state changes
   causing write spinners to restart their loop.
 - Write spinners are limited by a count while readers hold the lock as
   there is no way to know for certain whether readers are running still.
 - In the read path block if there are write waiters or spinners to avoid
   starving writers.  Use a new per-thread count, td_rw_rlocks, to skip
   starvation avoidance if it might cause a deadlock.
 - Remove or change invalid assertions in turnstiles.

Reviewed by:    attilio (developed parts of the patch as well)
Sponsored by:   Nokia
2008-02-06 01:02:13 +00:00
John Baldwin
cff3c4fdc5 Remove a conditional that is always true.
MFC after:	2 weeks
2008-01-17 20:15:15 +00:00
Jeff Roberson
eea4f254fe - Re-implement lock profiling in such a way that it no longer breaks
the ABI when enabled.  There is no longer an embedded lock_profile_object
   in each lock.  Instead a list of lock_profile_objects is kept per-thread
   for each lock it may own.  The cnt_hold statistic is now always 0 to
   facilitate this.
 - Support shared locking by tracking individual lock instances and
   statistics in the per-thread per-instance lock_profile_object.
 - Make the lock profiling hash table a per-cpu singly linked list with a
   per-cpu static lock_prof allocator.  This removes the need for an array
   of spinlocks and reduces cache contention between cores.
 - Use a seperate hash for spinlocks and other locks so that only a
   critical_enter() is required and not a spinlock_enter() to modify the
   per-cpu tables.
 - Count time spent spinning in the lock statistics.
 - Remove the LOCK_PROFILE_SHARED option as it is always supported now.
 - Specifically drop and release the scheduler locks in both schedulers
   since we track owners now.

In collaboration with:	Kip Macy
Sponsored by:	Nokia
2007-12-15 23:13:31 +00:00
Attilio Rao
49aead8a10 Simplify the adaptive spinning algorithm in rwlock and mutex:
currently, before to spin the turnstile spinlock is acquired and the
waiters flag is set.
This is not strictly necessary, so just spin before to acquire the
spinlock and to set the flags.
This will simplify a lot other functions too, as now we have the waiters
flag set only if there are actually waiters.
This should make wakeup/sleeping couplet faster under intensive mutex
workload.
This also fixes a bug in rw_try_upgrade() in the adaptive case, where
turnstile_lookup() will recurse on the ts_lock lock that will never be
really released [1].

[1] Reported by: jeff with Nokia help
Tested by: pho, kris (earlier, bugged version of rwlock part)
Discussed with: jhb [2], jeff
MFC after: 1 week

[2] John had a similar patch about 6.x and/or 7.x about mutexes probabilly
2007-11-26 22:37:35 +00:00
Attilio Rao
f9721b43ed Expand lock class with the "virtual" function lc_assert which will offer
an unified way for all the lock primitives to express lock assertions.
Currenty, lockmgrs and rmlocks don't have assertions, so just panic in
that case.
This will be a base for more callout improvements.

Ok'ed by: jhb, jeff
2007-11-18 14:43:53 +00:00
Attilio Rao
6f5c319c12 Remove a bogus KASSERT which will prevent rwlock to be acquired
recursively in exclusive mode with debugging kernels.

Submitted by: kmacy
Approved by: jeff
2007-11-14 21:21:48 +00:00
Julian Elischer
431f890614 generally we are interested in what thread did something as
opposed to what process. Since threads by default have teh name of the
process unless over-written with more useful information, just print the
thread name instead.
2007-11-14 06:21:24 +00:00
Attilio Rao
6aa294be2c Fix some problems with lock profiling in rw locks:
- Adjust lock_profiling stubs semantic in the hard functions in order to be
  more accurate and trustable
- As for sx locks, disable shared paths for lock_profiling.  Actually,
  lock_profiling has a subtle race which makes results caming from shared
  paths not completely trustable. A macro stub (LOCK_PROFILING_SHARED) can
  be actually used for re-enabling this paths, but is currently intended
  for developing use only.
- style(9) fixes

Approved by: jeff, kmacy, jhb[1]
Approved by: re

[1] Had initial reservations not shared by others, conceded
    in the end.
2007-07-20 08:43:42 +00:00
Attilio Rao
f08945a7d2 Introduce a new rwlocks initialization function: rw_init_flags.
This is very similar to sx_init_flags: it initializes the rwlock using
special flags passed as third argument (RW_DUPOK, RW_NOPROFILE,
RW_NOWITNESS, RW_QUIET, RW_RECURSE).
Among these, the most important new feature is probabilly that rwlocks
can be acquired recursively now (for both shared and exclusive paths).

Because of the recursion counter, the ABI is changed.

Tested by: Timothy Redaelli <drizzt@gufi.org>
Reviewed by: jhb
Approved by: jeff (mentor)
Approved by: re
2007-06-26 21:31:56 +00:00
Jeff Roberson
2502c107ba Commit 3/14 of sched_lock decomposition.
- Add a per-turnstile spinlock to solve potential priority propagation
   deadlocks that are possible with thread_lock().
 - The turnstile lock order is defined as the exact opposite of the
   lock order used with the sleep locks they represent.  This allows us
   to walk in reverse order in priority_propagate and this is the only
   place we wish to multiply acquire turnstile locks.
 - Use the turnstile_chain lock to protect assigning mutexes to turnstiles.
 - Change the turnstile interface to pass back turnstile pointers to the
   consumers.  This allows us to reduce some locking and makes it easier
   to cancel turnstile assignment while the turnstile chain lock is held.

Tested by:      kris, current@
Tested on:      i386, amd64, ULE, 4BSD, libthr, libkse, PREEMPTION, etc.
Discussed with: kris, attilio, kmacy, jhb, julian, bde (small parts each)
2007-06-04 23:51:44 +00:00
John Baldwin
c91fcee75d Move lock_profile_object_{init,destroy}() into lock_{init,destroy}(). 2007-05-18 15:04:59 +00:00
John Baldwin
0026c92c3e Add destroyed cookie values for sx locks and rwlocks as well as extra
KASSERTs so that any lock operations on a destroyed lock will panic or
hang.
2007-05-08 21:51:37 +00:00
John Baldwin
b80ad3eea1 - Drop memory barriers in rw_try_upgrade(). We don't need an 'acq' memory
barrier here as the earlier rw_rlock() already contained one.
- Comment fix.
2007-03-30 18:08:55 +00:00
John Baldwin
cd6e6e4e11 - Simplify the #ifdef's for adaptive mutexes and rwlocks by conditionally
defining a macro earlier in the file.
- Add NO_ADAPTIVE_RWLOCKS option to disable adaptive spinning for rwlocks.
2007-03-22 16:09:23 +00:00
John Baldwin
aa89d8cd52 Rename the 'mtx_object', 'rw_object', and 'sx_object' members of mutexes,
rwlocks, and sx locks to 'lock_object'.
2007-03-21 21:20:51 +00:00
John Baldwin
c1f2a5334d Print readers count as unsigned in ddb 'show lock'.
Submitted by:	attilio
2007-03-13 16:51:27 +00:00
John Baldwin
4b493b1a6d Fix a typo. 2007-03-12 20:10:29 +00:00
John Baldwin
6e21afd40c Add two new function pointers 'lc_lock' and 'lc_unlock' to lock classes.
These functions are intended to be used to drop a lock and then reacquire
it when doing an sleep such as msleep(9).  Both functions accept a
'struct lock_object *' as their first parameter.  The 'lc_unlock' function
returns an integer that is then passed as the second paramter to the
subsequent 'lc_lock' function.  This can be used to communicate state.
For example, sx locks and rwlocks use this to indicate if the lock was
share/read locked vs exclusive/write locked.

Currently, spin mutexes and lockmgr locks do not provide working lc_lock
and lc_unlock functions.
2007-03-09 16:27:11 +00:00
John Baldwin
ae8dde30c2 Use C99-style struct member initialization for lock classes. 2007-03-09 16:04:44 +00:00
John Baldwin
ddb38a1f3d Fix some nits in lock profiling for rwlocks:
- Properly note when a read lock is released.
- Always note when we contest on a read lock.
- Only note success of obtaining read locks for the first reader to match
  the behavior of sx(9).

Reviewed by:	kmacy
2007-03-07 20:48:48 +00:00
Kip Macy
f183910b97 Further improvements to LOCK_PROFILING:
- Fix missing initialization in kern_rwlock.c causing bogus times to be collected
 - Move updates to the lock hash to after the lock is released for spin mutexes,
   sleep mutexes, and sx locks
 - Add new kernel build option LOCK_PROFILE_FAST - only update lock profiling
   statistics when an acquisition is contended. This reduces the overhead of
   LOCK_PROFILING to increasing system time by 20%-25% which on
   "make -j8 kernel-toolchain" on a dual woodcrest is unmeasurable in terms
   of wall-clock time. Contrast this to enabling lock profiling without
   LOCK_PROFILE_FAST and I see a 5x-6x slowdown in wall-clock time.
2007-02-27 06:42:05 +00:00
Robert Watson
8525230afd Add rw_wowned() interface to rwlock(9), allowing a kernel thread to
determine if it holds an exclusive rwlock reference or not.  This is
non-ideal, but recursion scenarios in the network stack currently
require it.

Approved by:	jhb
2007-02-26 19:05:13 +00:00
Kip Macy
fe68a91631 general LOCK_PROFILING cleanup
- only collect timestamps when a lock is contested - this reduces the overhead
  of collecting profiles from 20x to 5x

- remove unused function from subr_lock.c

- generalize cnt_hold and cnt_lock statistics to be kept for all locks

- NOTE: rwlock profiling generates invalid statistics (and most likely always has)
  someone familiar with that should review
2007-02-26 08:26:44 +00:00
Kip Macy
61bd5e21b3 track lock class name in a way that doesn't break WITNESS 2006-11-13 05:41:46 +00:00
Kip Macy
7c0435b933 MUTEX_PROFILING has been generalized to LOCK_PROFILING. We now profile
wait (time waited to acquire) and hold times for *all* kernel locks. If
the architecture has a system synchronized TSC, the profiling code will
use that - thereby minimizing profiling overhead. Large chunks of profiling
code have been moved out of line, the overhead measured on the T1 for when
it is compiled in but not enabled is < 1%.

Approved by: scottl (standing in for mentor rwatson)
Reviewed by: des and jhb
2006-11-11 03:18:07 +00:00
John Baldwin
764e4d54e9 Adjust td_locks for non-spin mutexes, rwlocks, and sx locks so that it is
a count of all non-spin locks, not just lockmgr locks.  This can give us a
much cheaper way to see if we have any locks held (such as when returning
to userland via userret()) without requiring WITNESS.

MFC after:	1 week
2006-07-27 21:45:55 +00:00
John Baldwin
fea3efe5bf Implement rw_try_upgrade() and rw_downgrade(). rw_try_upgrade() makes a
single attempt at upgrading a read lock to a write lock, and rw_downgrade()
converts curthread's write lock into a read lock.
2006-04-19 21:06:52 +00:00
Wojciech A. Koszek
5884c1a098 'owner' is not used without SMP. Fix kernel build for such kernel
configurations.

Approved by:	jhb
2006-04-18 20:32:42 +00:00
John Baldwin
efa86db61d Adaptively spin before blocking on the turnstile if an rwlock is write
locked.  In general the adaptive spinning is similar to the same code
for mutexes with some extra trickiness in rw_wunlock_hard().  Specifically,
even though both wait bits might be set and we might have a turnstile with
at least one waiting thread, there might not be any threads blocked on the
queue we are not waking up (they might all be spinning), and we should
only preserve the waiting flag for the queue we aren't waking up if there
are in fact threads blocked on that queue.  Secondly, there might not be
any threads blocked on the queue we have chosen to waken threads from
(there might only be threads blocked on the other queue and the threads
for this queue are all spinning) in which case we disown the turnstile
instead of doing a braodcast and unpend.
2006-04-18 18:27:54 +00:00
John Baldwin
38bf165fa1 - Add a rw_wowner() macro that just returns the owner of a write lock and
use it in places that only care about the write owner instead of
  rw_owner() as a baby step towards limited read-lock owner.
- Tidy the code that sets the WAITER flag bits to not duplicate a test
  around the atomic operation and the KTR trace in both of the lock
  functions.
2006-04-17 21:11:01 +00:00
Scott Long
803e980d03 Fix another compile problem. If I find any more, this file is going in the
Attic until it is properly fixed.
2006-02-01 04:18:07 +00:00
Scott Long
019a2f40ae Regroup order of operations to better reflect what was probably intended.
Submitted by: Peter Jeremy
2006-01-30 19:25:52 +00:00
Scott Long
8ad6b7ab7c Take a stab at making this compile when WITNESS is not defined. gcc can't
figure out the order of operations at line 519, and neither can I, but this
is my best guess.  Also correct a number of typos and syntax errors.
2006-01-29 20:48:25 +00:00