Commit Graph

41 Commits

Author SHA1 Message Date
Robin Holt e8c158bb31 Factor out #ifdefs from kernel/spinlock.c to LOCK_CONTENDED_FLAGS
SGI has observed that on large systems, interrupts are not serviced for a
long period of time when waiting for a rwlock.  The following patch series
re-enables irqs while waiting for the lock, resembling the code which is
already there for spinlocks.

I only made the ia64 version, because the patch adds some overhead to the
fast path.  I assume there is currently no demand to have this for other
architectures, because the systems are not so large.  Of course, the
possibility to implement raw_{read|write}_lock_flags for any architecture
is still there.

This patch:

The new macro LOCK_CONTENDED_FLAGS expands to the correct implementation
depending on the config options, so that IRQ's are re-enabled when
possible, but they remain disabled if CONFIG_LOCKDEP is set.

Signed-off-by: Petr Tesarik <ptesarik@suse.cz>
Signed-off-by: Robin Holt <holt@sgi.com>
Cc: <linux-arch@vger.kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Luck, Tony" <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2009-04-02 19:05:10 -07:00
Peter Zijlstra 9851673bc3 lockdep: move state bit definitions around
For convenience later.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-02-14 23:27:59 +01:00
Peter Zijlstra a652d7081b lockdep: sanitize reclaim bit names
s/HELD_OVER/ENABLED/g

so that its similar to the hard and soft-irq names.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-02-14 23:27:52 +01:00
Peter Zijlstra 4fc95e867f lockdep: sanitize bit names
s/\(LOCKF\?_ENABLED_[^ ]*\)S\(_READ\)\?\>/\1\2/g

So that the USED_IN and ENABLED have the same names.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-02-14 23:27:51 +01:00
Nick Piggin cf40bd16fd lockdep: annotate reclaim context (__GFP_NOFS)
Here is another version, with the incremental patch rolled up, and
added reclaim context annotation to kswapd, and allocation tracing
to slab allocators (which may only ever reach the page allocator
in rare cases, so it is good to put annotations here too).

Haven't tested this version as such, but it should be getting closer
to merge worthy ;)

--
After noticing some code in mm/filemap.c accidentally perform a __GFP_FS
allocation when it should not have been, I thought it might be a good idea to
try to catch this kind of thing with lockdep.

I coded up a little idea that seems to work. Unfortunately the system has to
actually be in __GFP_FS page reclaim, then take the lock, before it will mark
it. But at least that might still be some orders of magnitude more common
(and more debuggable) than an actual deadlock condition, so we have some
improvement I hope (the concept is no less complete than discovery of a lock's
interrupt contexts).

I guess we could even do the same thing with __GFP_IO (normal reclaim), and
even GFP_NOIO locks too... but filesystems will have the most locks and fiddly
code paths, so let's start there and see how it goes.

It *seems* to work. I did a quick test.

=================================
[ INFO: inconsistent lock state ]
2.6.28-rc6-00007-ged31348-dirty #26
---------------------------------
inconsistent {in-reclaim-W} -> {ov-reclaim-W} usage.
modprobe/8526 [HC0[0]:SC0[0]:HE1:SE1] takes:
 (testlock){--..}, at: [<ffffffffa0020055>] brd_init+0x55/0x216 [brd]
{in-reclaim-W} state was registered at:
  [<ffffffff80267bdb>] __lock_acquire+0x75b/0x1a60
  [<ffffffff80268f71>] lock_acquire+0x91/0xc0
  [<ffffffff8070f0e1>] mutex_lock_nested+0xb1/0x310
  [<ffffffffa002002b>] brd_init+0x2b/0x216 [brd]
  [<ffffffff8020903b>] _stext+0x3b/0x170
  [<ffffffff80272ebf>] sys_init_module+0xaf/0x1e0
  [<ffffffff8020c3fb>] system_call_fastpath+0x16/0x1b
  [<ffffffffffffffff>] 0xffffffffffffffff
irq event stamp: 3929
hardirqs last  enabled at (3929): [<ffffffff8070f2b5>] mutex_lock_nested+0x285/0x310
hardirqs last disabled at (3928): [<ffffffff8070f089>] mutex_lock_nested+0x59/0x310
softirqs last  enabled at (3732): [<ffffffff8061f623>] sk_filter+0x83/0xe0
softirqs last disabled at (3730): [<ffffffff8061f5b6>] sk_filter+0x16/0xe0

other info that might help us debug this:
1 lock held by modprobe/8526:
 #0:  (testlock){--..}, at: [<ffffffffa0020055>] brd_init+0x55/0x216 [brd]

stack backtrace:
Pid: 8526, comm: modprobe Not tainted 2.6.28-rc6-00007-ged31348-dirty #26
Call Trace:
 [<ffffffff80265483>] print_usage_bug+0x193/0x1d0
 [<ffffffff80266530>] mark_lock+0xaf0/0xca0
 [<ffffffff80266735>] mark_held_locks+0x55/0xc0
 [<ffffffffa0020000>] ? brd_init+0x0/0x216 [brd]
 [<ffffffff802667ca>] trace_reclaim_fs+0x2a/0x60
 [<ffffffff80285005>] __alloc_pages_internal+0x475/0x580
 [<ffffffff8070f29e>] ? mutex_lock_nested+0x26e/0x310
 [<ffffffffa0020000>] ? brd_init+0x0/0x216 [brd]
 [<ffffffffa002006a>] brd_init+0x6a/0x216 [brd]
 [<ffffffffa0020000>] ? brd_init+0x0/0x216 [brd]
 [<ffffffff8020903b>] _stext+0x3b/0x170
 [<ffffffff8070f8b9>] ? mutex_unlock+0x9/0x10
 [<ffffffff8070f83d>] ? __mutex_unlock_slowpath+0x10d/0x180
 [<ffffffff802669ec>] ? trace_hardirqs_on_caller+0x12c/0x190
 [<ffffffff80272ebf>] sys_init_module+0xaf/0x1e0
 [<ffffffff8020c3fb>] system_call_fastpath+0x16/0x1b

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2009-02-14 23:27:49 +01:00
Linus Torvalds 179475a3b4 Merge branch 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip
* 'irq-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  x86, sparseirq: clean up Kconfig entry
  x86: turn CONFIG_SPARSE_IRQ off by default
  sparseirq: fix numa_migrate_irq_desc dependency and comments
  sparseirq: add kernel-doc notation for new member in irq_desc, -v2
  locking, irq: enclose irq_desc_lock_class in CONFIG_LOCKDEP
  sparseirq, xen: make sure irq_desc is allocated for interrupts
  sparseirq: fix !SMP building, #2
  x86, sparseirq: move irq_desc according to smp_affinity, v7
  proc: enclose desc variable of show_stat() in CONFIG_SPARSE_IRQ
  sparse irqs: add irqnr.h to the user headers list
  sparse irqs: handle !GENIRQ platforms
  sparseirq: fix !SMP && !PCI_MSI && !HT_IRQ build
  sparseirq: fix Alpha build failure
  sparseirq: fix typo in !CONFIG_IO_APIC case
  x86, MSI: pass irq_cfg and irq_desc
  x86: MSI start irq numbering from nr_irqs_gsi
  x86: use NR_IRQS_LEGACY
  sparse irq_desc[] array: core kernel and x86 changes
  genirq: record IRQ_LEVEL in irq_desc[]
  irq.h: remove padding from irq_desc on 64bits
2008-12-30 16:20:19 -08:00
KOSAKI Motohiro 74c8a61304 locking, irq: enclose irq_desc_lock_class in CONFIG_LOCKDEP
Impact: simplify code

commit "08678b0: generic: sparse irqs: use irq_desc() [...]" introduced
the irq_desc_lock_class variable.

But it is used only if CONFIG_SPARSE_IRQ=Y or CONFIG_TRACE_IRQFLAGS=Y.
Otherwise, following warnings happen:

	CC      kernel/irq/handle.o
	kernel/irq/handle.c:26: warning: 'irq_desc_lock_class' defined but not used

Actually, current early_init_irq_lock_class has a bit strange and messy ifdef.
In addition, it is not valueable.

1. this function is protected by !CONFIG_SPARSE_IRQ, but that is not necessary.
   if CONFIG_SPARSE_IRQ=Y, desc of all irq number are initialized by NULL
   at first - then this function calling is safe.

2. this function protected by CONFIG_TRACE_IRQFLAGS too. but it is not
   necessary either, because lockdep_set_class() doesn't have bad side
   effect even if CONFIG_TRACE_IRQFLAGS=n.

This patch bloat kernel size a bit on CONFIG_TRACE_IRQFLAGS=n and
CONFIG_SPARSE_IRQ=Y - but that's ok. early_init_irq_lock_class() is not
a fastpatch at all.

To avoid messy ifdefs is more important than a few bytes diet.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-12-18 14:35:53 +01:00
Peter Zijlstra 00ef9f7348 lockdep: change a held lock's class
Impact: introduce new lockdep API

Allow to change a held lock's class. Basically the same as the existing
code to change a subclass therefore reuse all that.

The XFS code will be able to use this to annotate their inode locking.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-12-04 10:08:18 +01:00
Ingo Molnar e8f6fbf62d lockdep: include/linux/lockdep.h - fix warning in net/bluetooth/af_bluetooth.c
fix this warning:

  net/bluetooth/af_bluetooth.c:60: warning: ‘bt_key_strings’ defined but not used
  net/bluetooth/af_bluetooth.c:71: warning: ‘bt_slock_key_strings’ defined but not used

this is a lockdep macro problem in the !LOCKDEP case.

We cannot convert it to an inline because the macro works on multiple types,
but we can mark the parameter used.

[ also clean up a misaligned tab in sock_lock_init_class_and_name() ]

[ also remove #ifdefs from around af_family_clock_key strings - which
  were certainly added to get rid of the ugly build warnings. ]

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: David S. Miller <davem@davemloft.net>
2008-11-13 23:19:10 -08:00
Ingo Molnar e25cf3db56 lockdep: include/linux/lockdep.h - fix warning in net/bluetooth/af_bluetooth.c
fix this warning:

  net/bluetooth/af_bluetooth.c:60: warning: ‘bt_key_strings’ defined but not used
  net/bluetooth/af_bluetooth.c:71: warning: ‘bt_slock_key_strings’ defined but not used

this is a lockdep macro problem in the !LOCKDEP case.

We cannot convert it to an inline because the macro works on multiple types,
but we can mark the parameter used.

[ also clean up a misaligned tab in sock_lock_init_class_and_name() ]

[ also remove #ifdefs from around af_family_clock_key strings - which
  were certainly added to get rid of the ugly build warnings. ]

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-11-12 12:39:40 +01:00
Peter Zijlstra c7e78cff6b lockstat: contend with points
We currently only provide points that have to wait on contention, also
lists the points we have to wait for.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-10-20 15:43:10 +02:00
Peter Zijlstra 76b189e918 lockdep: add might_lock() / might_lock_read()
useful to establish a lock dependency in case the actual dependency is
rare or hard to trigger.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-09-10 13:48:49 +02:00
Ingo Molnar e5f363e358 lockdep: increase MAX_LOCKDEP_KEYS
certain configs produce:

 [   70.076229] BUG: MAX_LOCKDEP_KEYS too low!
 [   70.080230] turning off the locking correctness validator.

tune them up.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-11 15:25:07 +02:00
Peter Zijlstra b42e737e57 lockdep: fix overflow in the hlock shrinkage code
There is a overflow by 1 case in the new shrunken hlock code.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-11 12:34:42 +02:00
Ingo Molnar 3295f0ef9f lockdep: rename map_[acquire|release]() => lock_map_[acquire|release]()
the names were too generic:

 drivers/uio/uio.c:87: error: expected identifier or '(' before 'do'
 drivers/uio/uio.c:87: error: expected identifier or '(' before 'while'
 drivers/uio/uio.c:113: error: 'map_release' undeclared here (not in a function)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-11 10:30:30 +02:00
Peter Zijlstra b7d39aff91 lockdep: spin_lock_nest_lock()
Expose the new lock protection lock.

This can be used to annotate places where we take multiple locks of the
same class and avoid deadlocks by always taking another (top-level) lock
first.

NOTE: we're still bound to the MAX_LOCK_DEPTH (48) limit.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-11 09:30:24 +02:00
Peter Zijlstra 7531e2f34d lockdep: lock protection locks
On Fri, 2008-08-01 at 16:26 -0700, Linus Torvalds wrote:

> On Fri, 1 Aug 2008, David Miller wrote:
> >
> > Taking more than a few locks of the same class at once is bad
> > news and it's better to find an alternative method.
>
> It's not always wrong.
>
> If you can guarantee that anybody that takes more than one lock of a
> particular class will always take a single top-level lock _first_, then
> that's all good. You can obviously screw up and take the same lock _twice_
> (which will deadlock), but at least you cannot get into ABBA situations.
>
> So maybe the right thing to do is to just teach lockdep about "lock
> protection locks". That would have solved the multi-queue issues for
> networking too - all the actual network drivers would still have taken
> just their single queue lock, but the one case that needs to take all of
> them would have taken a separate top-level lock first.
>
> Never mind that the multi-queue locks were always taken in the same order:
> it's never wrong to just have some top-level serialization, and anybody
> who needs to take <n> locks might as well do <n+1>, because they sure as
> hell aren't going to be on _any_ fastpaths.
>
> So the simplest solution really sounds like just teaching lockdep about
> that one special case. It's not "nesting" exactly, although it's obviously
> related to it.

Do as Linus suggested. The lock protection lock is called nest_lock.

Note that we still have the MAX_LOCK_DEPTH (48) limit to consider, so anything
that spills that it still up shit creek.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-11 09:30:24 +02:00
Peter Zijlstra 4f3e7524b2 lockdep: map_acquire
Most the free-standing lock_acquire() usages look remarkably similar, sweep
them into a new helper.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-11 09:30:23 +02:00
Dave Jones f82b217e35 lockdep: shrink held_lock structure
struct held_lock {
        u64                        prev_chain_key;       /*     0     8 */
        struct lock_class *        class;                /*     8     8 */
        long unsigned int          acquire_ip;           /*    16     8 */
        struct lockdep_map *       instance;             /*    24     8 */
        int                        irq_context;          /*    32     4 */
        int                        trylock;              /*    36     4 */
        int                        read;                 /*    40     4 */
        int                        check;                /*    44     4 */
        int                        hardirqs_off;         /*    48     4 */

        /* size: 56, cachelines: 1 */
        /* padding: 4 */
        /* last cacheline: 56 bytes */
};

struct held_lock {
        u64                        prev_chain_key;       /*     0     8 */
        long unsigned int          acquire_ip;           /*     8     8 */
        struct lockdep_map *       instance;             /*    16     8 */
        unsigned int               class_idx:11;         /*    24:21  4 */
        unsigned int               irq_context:2;        /*    24:19  4 */
        unsigned int               trylock:1;            /*    24:18  4 */
        unsigned int               read:2;               /*    24:16  4 */
        unsigned int               check:2;              /*    24:14  4 */
        unsigned int               hardirqs_off:1;       /*    24:13  4 */

        /* size: 32, cachelines: 1 */
        /* padding: 4 */
        /* bit_padding: 13 bits */
        /* last cacheline: 32 bytes */
};

[mingo@elte.hu: shrunk hlock->class too]
[peterz@infradead.org: fixup bit sizes]
Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
2008-08-11 09:30:23 +02:00
Peter Zijlstra 64aa348edc lockdep: lock_set_subclass - reset a held lock's subclass
this can be used to reset a held lock's subclass, for arbitrary-depth
iterated data structures such as trees or lists which have per-node
locks.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-08-11 09:30:21 +02:00
David Miller 419ca3f135 lockdep: fix combinatorial explosion in lock subgraph traversal
When we traverse the graph, either forwards or backwards, we
are interested in whether a certain property exists somewhere
in a node reachable in the graph.

Therefore it is never necessary to traverse through a node more
than once to get a correct answer to the given query.

Take advantage of this property using a global ID counter so that we
need not clear all the markers in all the lock_class entries before
doing a traversal.  A new ID is choosen when we start to traverse, and
we continue through a lock_class only if it's ID hasn't been marked
with the new value yet.

This short-circuiting is essential especially for high CPU count
systems.  The scheduler has a runqueue per cpu, and needs to take
two runqueue locks at a time, which leads to long chains of
backwards and forwards subgraphs from these runqueue lock nodes.
Without the short-circuit implemented here, a graph traversal on
a runqueue lock can take up to (1 << (N - 1)) checks on a system
with N cpus.

For anything more than 16 cpus or so, lockdep will eventually bring
the machine to a complete standstill.

Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-31 18:38:28 +02:00
Li Zefan a033c332e0 lockdep: remove duplicate definition of STATIC_LOCKDEP_MAP_INIT
STATIC_LOCKDEP_MAP_INIT is defined twice in lockdep.h. I guess
it's a copy & paste.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-06-24 13:43:07 +02:00
Huang, Ying 443cd507ce lockdep: add lock_class information to lock_chain and output it
This patch records array of lock_class into lock_chain, and export
lock_chain information via /proc/lockdep_chains.

It is based on x86/master branch of git-x86 tree, and has been tested
on x86_64 platform.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-06-20 12:21:33 +02:00
Johannes Berg 4e6045f134 workqueue: debug flushing deadlocks with lockdep
In the following scenario:

code path 1:
  my_function() -> lock(L1); ...; flush_workqueue(); ...

code path 2:
  run_workqueue() -> my_work() -> ...; lock(L1); ...

you can get a deadlock when my_work() is queued or running
but my_function() has acquired L1 already.

This patch adds a pseudo-lock to each workqueue to make lockdep
warn about this scenario.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-10-19 11:53:38 -07:00
Peter Zijlstra 851a67b825 lockdep: annotate rcu_read_{,un}lock{,_bh}
lockdep annotate rcu_read_{,un}lock{,_bh} in order to catch imbalanced
usage.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2007-10-11 22:11:12 +02:00
Peter Zijlstra b351d164e8 lockdep: syscall exit check
Provide a check to validate that we do not hold any locks when switching
back to user-space.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2007-10-11 22:11:12 +02:00
Peter Zijlstra 96645678cd lockstat: measure lock bouncing
__acquire
        |
       lock _____
        |        \
        |    __contended
        |         |
        |        wait
        | _______/
        |/
        |
   __acquired
        |
   __release
        |
     unlock

We measure acquisition and contention bouncing.

This is done by recording a cpu stamp in each lock instance.

Contention bouncing requires the cpu stamp to be set on acquisition. Hence we
move __acquired into the generic path.

__acquired is then used to measure acquisition bouncing by comparing the
current cpu with the old stamp before replacing it.

__contended is used to measure contention bouncing (only useful for preemptable
locks)

[akpm@linux-foundation.org: cleanups]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-07-19 10:04:49 -07:00
Peter Zijlstra 4b32d0a4e9 lockdep: various fixes
- update the copyright notices
 - use the default hash function
 - fix a thinko in a BUILD_BUG_ON
 - add a WARN_ON to spot inconsitent naming
 - fix a termination issue in /proc/lock_stat

[akpm@linux-foundation.org: cleanups]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-07-19 10:04:49 -07:00
Peter Zijlstra f20786ff4d lockstat: core infrastructure
Introduce the core lock statistics code.

Lock statistics provides lock wait-time and hold-time (as well as the count
of corresponding contention and acquisitions events). Also, the first few
call-sites that encounter contention are tracked.

Lock wait-time is the time spent waiting on the lock. This provides insight
into the locking scheme, that is, a heavily contended lock is indicative of
a too coarse locking scheme.

Lock hold-time is the duration the lock was held, this provides a reference for
the wait-time numbers, so they can be put into perspective.

  1)
    lock
  2)
    ... do stuff ..
    unlock
  3)

The time between 1 and 2 is the wait-time. The time between 2 and 3 is the
hold-time.

The lockdep held-lock tracking code is reused, because it already collects locks
into meaningful groups (classes), and because it is an existing infrastructure
for lock instrumentation.

Currently lockdep tracks lock acquisition with two hooks:

  lock()
    lock_acquire()
    _lock()

 ... code protected by lock ...

  unlock()
    lock_release()
    _unlock()

We need to extend this with two more hooks, in order to measure contention.

  lock_contended() - used to measure contention events
  lock_acquired()  - completion of the contention

These are then placed the following way:

  lock()
    lock_acquire()
    if (!_try_lock())
      lock_contended()
      _lock()
      lock_acquired()

 ... do locked stuff ...

  unlock()
    lock_release()
    _unlock()

(Note: the try_lock() 'trick' is used to avoid instrumenting all platform
       dependent lock primitive implementations.)

It is also possible to toggle the two lockdep features at runtime using:

  /proc/sys/kernel/prove_locking
  /proc/sys/kernel/lock_stat

(esp. turning off the O(n^2) prove_locking functionaliy can help)

[akpm@linux-foundation.org: build fixes]
[akpm@linux-foundation.org: nuke unneeded ifdefs]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-07-19 10:04:49 -07:00
Jarek Poplawski e3a55fd18d [PATCH] lockdep: lockdep_depth vs. debug_locks
lockdep found a bug during a run of workqueue function - this could be also
caused by a bug from other code running simultaneously.

lockdep really shouldn't be used when debug_locks == 0!

Reported-by: Folkert van Heusden <folkert@vanheusden.com>
Inspired-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Jarek Poplawski <jarkao2@o2.pl>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-03-22 19:39:06 -07:00
Heiko Carstens a1e96b0310 [PATCH] lockdep: forward declare struct task_struct
3117df0453 causes this:

In file included from arch/s390/kernel/early.c:13:
include/linux/lockdep.h:300: warning:
		"struct task_struct" declared inside parameter list
include/linux/lockdep.h:300:
		warning: its scope is only this definition or
		declaration, which is probably not what you want

Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-02-12 09:48:29 -08:00
Jason Baron 068135e635 [PATCH] lockdep: add graph depth information to /proc/lockdep
Generate locking graph information into /proc/lockdep, for lock hierarchy
documentation and visualization purposes.

sample output:

 c089fd5c OPS:     138 FD:   14 BD:    1 --..: &tty->termios_mutex
  -> [c07a3430] tty_ldisc_lock
  -> [c07a37f0] &port_lock_key
  -> [c07afdc0] &rq->rq_lock_key#2

The lock classes listed are all the first-hop lock dependencies that
lockdep has seen so far.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-02-11 10:51:26 -08:00
Ingo Molnar 3117df0453 [PATCH] lockdep: print irq-trace info on asserts
When we print an assert due to scheduling-in-atomic bugs, and if lockdep
is enabled, then the IRQ tracing information of lockdep can be printed
to pinpoint the code location that disabled interrupts. This saved me
quite a bit of debugging time in cases where the backtrace did not
identify the irq-disabling site well enough.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-12-13 09:05:50 -08:00
Adrian Bunk ebe7e5fe4b [PATCH] remove kernel/lockdep.c:lockdep_internal
Remove the no longer used lockdep_internal().

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-12-07 08:39:39 -08:00
Peter Zijlstra d5abe66917 [PATCH] debug: workqueue locking sanity
Workqueue functions should not leak locks, assert so, printing the
last function ran.

Use macros in lockdep.h to avoid include dependency pains.

[akpm@osdl.org: build fix]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-12-07 08:39:36 -08:00
Andrew Morton 07646e217f Lockdep: fix compile error in drivers/input/serio/serio.c
lockdep_set_subclass() was missing in !LOCKDEP case

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
2006-10-11 23:45:23 -04:00
Peter Zijlstra 4dfbb9d8c6 Lockdep: add lockdep_set_class_and_subclass() and lockdep_set_subclass()
This annotation makes it possible to assign a subclass on lock init. This
annotation is meant to reduce the _nested() annotations by assigning a
default subclass.

One could do without this annotation and rely on lockdep_set_class()
exclusively, but that would require a manual stack of struct lock_class_key
objects.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
2006-10-11 01:45:14 -04:00
Michael S. Tsirkin db0b0ead60 [PATCH] lockdep: don't pull in includes when lockdep disabled
Do not pull in various includes through lockdep.h if lockdep is disabled.

Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-09-29 09:18:08 -07:00
Ingo Molnar d6d897cec2 [PATCH] lockdep: core, reduce per-lock class-cache size
lockdep_map is embedded into every lock, which blows up data structure
sizes all around the kernel.  Reduce the class-cache to be for the default
class only - that is used in 99.9% of the cases and even if we dont have a
class cached, the lookup in the class-hash is lockless.

This change reduces the per-lock dep_map overhead by 56 bytes on 64-bit
platforms and by 28 bytes on 32-bit platforms.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-07-10 13:24:14 -07:00
Ingo Molnar 243c7621aa [PATCH] lockdep: annotate genirq
Teach special (recursive) locking code to the lock validator.  Has no effect
on non-lockdep kernels.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-07-03 15:27:06 -07:00
Ingo Molnar fbb9ce9530 [PATCH] lockdep: core
Do 'make oldconfig' and accept all the defaults for new config options -
reboot into the kernel and if everything goes well it should boot up fine and
you should have /proc/lockdep and /proc/lockdep_stats files.

Typically if the lock validator finds some problem it will print out
voluminous debug output that begins with "BUG: ..." and which syslog output
can be used by kernel developers to figure out the precise locking scenario.

What does the lock validator do?  It "observes" and maps all locking rules as
they occur dynamically (as triggered by the kernel's natural use of spinlocks,
rwlocks, mutexes and rwsems).  Whenever the lock validator subsystem detects a
new locking scenario, it validates this new rule against the existing set of
rules.  If this new rule is consistent with the existing set of rules then the
new rule is added transparently and the kernel continues as normal.  If the
new rule could create a deadlock scenario then this condition is printed out.

When determining validity of locking, all possible "deadlock scenarios" are
considered: assuming arbitrary number of CPUs, arbitrary irq context and task
context constellations, running arbitrary combinations of all the existing
locking scenarios.  In a typical system this means millions of separate
scenarios.  This is why we call it a "locking correctness" validator - for all
rules that are observed the lock validator proves it with mathematical
certainty that a deadlock could not occur (assuming that the lock validator
implementation itself is correct and its internal data structures are not
corrupted by some other kernel subsystem).  [see more details and conditionals
of this statement in include/linux/lockdep.h and
Documentation/lockdep-design.txt]

Furthermore, this "all possible scenarios" property of the validator also
enables the finding of complex, highly unlikely multi-CPU multi-context races
via single single-context rules, increasing the likelyhood of finding bugs
drastically.  In practical terms: the lock validator already found a bug in
the upstream kernel that could only occur on systems with 3 or more CPUs, and
which needed 3 very unlikely code sequences to occur at once on the 3 CPUs.
That bug was found and reported on a single-CPU system (!).  So in essence a
race will be found "piecemail-wise", triggering all the necessary components
for the race, without having to reproduce the race scenario itself!  In its
short existence the lock validator found and reported many bugs before they
actually caused a real deadlock.

To further increase the efficiency of the validator, the mapping is not per
"lock instance", but per "lock-class".  For example, all struct inode objects
in the kernel have inode->inotify_mutex.  If there are 10,000 inodes cached,
then there are 10,000 lock objects.  But ->inotify_mutex is a single "lock
type", and all locking activities that occur against ->inotify_mutex are
"unified" into this single lock-class.  The advantage of the lock-class
approach is that all historical ->inotify_mutex uses are mapped into a single
(and as narrow as possible) set of locking rules - regardless of how many
different tasks or inode structures it took to build this set of rules.  The
set of rules persist during the lifetime of the kernel.

To see the rough magnitude of checking that the lock validator does, here's a
portion of /proc/lockdep_stats, fresh after bootup:

 lock-classes:                            694 [max: 2048]
 direct dependencies:                  1598 [max: 8192]
 indirect dependencies:               17896
 all direct dependencies:             16206
 dependency chains:                    1910 [max: 8192]
 in-hardirq chains:                      17
 in-softirq chains:                     105
 in-process chains:                    1065
 stack-trace entries:                 38761 [max: 131072]
 combined max dependencies:         2033928
 hardirq-safe locks:                     24
 hardirq-unsafe locks:                  176
 softirq-safe locks:                     53
 softirq-unsafe locks:                  137
 irq-safe locks:                         59
 irq-unsafe locks:                      176

The lock validator has observed 1598 actual single-thread locking patterns,
and has validated all possible 2033928 distinct locking scenarios.

More details about the design of the lock validator can be found in
Documentation/lockdep-design.txt, which can also found at:

   http://redhat.com/~mingo/lockdep-patches/lockdep-design.txt

[bunk@stusta.de: cleanups]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-07-03 15:27:03 -07:00