On Sun, 2011-07-24 at 21:06 -0400, Arnaud Lacombe wrote:
> /src/linux/linux/kernel/lockdep.c: In function 'mark_held_locks':
> /src/linux/linux/kernel/lockdep.c:2471:31: warning: comparison of
> distinct pointer types lacks a cast
The warning is harmless in this case, but the below makes it go away.
Reported-by: Arnaud Lacombe <lacombar@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1311588599.2617.56.camel@laptop
Signed-off-by: Ingo Molnar <mingo@elte.hu>
The main lock_is_held() user is lockdep_assert_held(), avoid false
assertions in lockdep_off() sections by unconditionally reporting the
lock is taken.
[ the reason this is important is a lockdep_assert_held() in ttwu()
which triggers a warning under lockdep_off() as in printk() which
can trigger another wakeup and lock up due to spinlock
recursion, as reported and heroically debugged by Arne Jansen ]
Reported-and-tested-by: Arne Jansen <lists@die-jansens.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: <stable@kernel.org>
Link: http://lkml.kernel.org/r/1307398759.2497.966.camel@laptop
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Lockdep output can be pretty cryptic, having nicer output
can save a lot of head scratching. When a simple irq inversion
scenario is detected by lockdep (lock A taken in interrupt
context but also in thread context without disabling interrupts)
we now get the following (hopefully more informative) output:
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(lockA);
<Interrupt>
lock(lockA);
*** DEADLOCK ***
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110421014300.436140880@goodmis.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Irq inversion and irq dependency bugs are only subtly
different. The diffenerence lies where the interrupt occurred.
For irq dependency:
irq_disable
lock(A)
lock(B)
unlock(B)
unlock(A)
irq_enable
lock(B)
unlock(B)
<interrupt>
lock(A)
The interrupt comes in after it has been established that lock A
can be held when taking an irq unsafe lock. Lockdep detects the
problem when taking lock A in interrupt context.
With the irq_inversion the irq happens before it is established
and lockdep detects the problem with the taking of lock B:
<interrupt>
lock(A)
irq_disable
lock(A)
lock(B)
unlock(B)
unlock(A)
irq_enable
lock(B)
unlock(B)
Since the problem with the locking logic for both of these issues
is in actuality the same, they both should report the same scenario.
This patch implements that and prints this:
other info that might help us debug this:
Chain exists of:
&rq->lock --> lockA --> lockC
Possible interrupt unsafe locking scenario:
CPU0 CPU1
---- ----
lock(lockC);
local_irq_disable();
lock(&rq->lock);
lock(lockA);
<Interrupt>
lock(&rq->lock);
*** DEADLOCK ***
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110421014259.910720381@goodmis.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
The lockdep output can be pretty cryptic, having nicer output
can save a lot of head scratching. When a normal deadlock
scenario is detected by lockdep (lock A -> lock B and there
exists a place where lock B -> lock A) we now get the following
new output:
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(lockB);
lock(lockA);
lock(lockB);
lock(lockA);
*** DEADLOCK ***
On cases where there's a deeper chair, it shows the partial
chain that can cause the issue:
Chain exists of:
lockC --> lockA --> lockB
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(lockB);
lock(lockA);
lock(lockB);
lock(lockC);
*** DEADLOCK ***
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110421014259.380621789@goodmis.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Locking order inversion due to interrupts is a subtle problem.
When an irq lockiinversion discovered by lockdep it currently
reports something like:
[ INFO: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected ]
... and then prints out the locks that are involved, as back traces.
Judging by lkml feedback developers were routinely confused by what
a HARDIRQ->safe to unsafe issue is all about, and sometimes even
blew it off as a bug in lockdep.
It is not obvious when lockdep prints this message about a lock that
is never taken in interrupt context.
After explaining the problems that lockdep is reporting, I
decided to add a description of the problem in visual form. Now
the following is shown:
---
other info that might help us debug this:
Possible interrupt unsafe locking scenario:
CPU0 CPU1
---- ----
lock(lockA);
local_irq_disable();
lock(&rq->lock);
lock(lockA);
<Interrupt>
lock(&rq->lock);
*** DEADLOCK ***
---
The above is the case when the unsafe lock is taken while
holding a lock taken in irq context. But when a lock is taken
that also grabs a unsafe lock, the call chain is shown:
---
other info that might help us debug this:
Chain exists of:
&rq->lock --> lockA --> lockC
Possible interrupt unsafe locking scenario:
CPU0 CPU1
---- ----
lock(lockC);
local_irq_disable();
lock(&rq->lock);
lock(lockA);
<Interrupt>
lock(&rq->lock);
*** DEADLOCK ***
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110421014259.132728798@goodmis.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>
During early boot, local IRQ is disabled until IRQ subsystem is
properly initialized. During this time, no one should enable
local IRQ and some operations which usually are not allowed with
IRQ disabled, e.g. operations which might sleep or require
communications with other processors, are allowed.
lockdep tracked this with early_boot_irqs_off/on() callbacks.
As other subsystems need this information too, move it to
init/main.c and make it generally available. While at it,
toggle the boolean to early_boot_irqs_disabled instead of
enabled so that it can be initialized with %false and %true
indicates the exceptional condition.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20110120110635.GB6036@htj.dyndns.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Current look_up_lock_class() doesn't check the parameter "subclass".
This rarely rises problems because the main caller of this function,
register_lock_class(), checks it.
But register_lock_class() is not the only function which calls
look_up_lock_class(). lock_set_class() and its callees also call it.
And lock_set_class() doesn't check this parameter.
This will rise problems when the the value of subclass is larger than
MAX_LOCKDEP_SUBCLASSES. Because the address (used as the key of class)
caliculated with too large subclass has a probability to point
another key in different lock_class_key.
Of course this problem depends on the memory layout and
occurs with really low probability.
Signed-off-by: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: Dmitry Torokhov <dtor@mail.ru>
Cc: Vojtech Pavlik <vojtech@ucw.cz>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1286958626-986-1-git-send-email-mitake@dcl.info.waseda.ac.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Current lockdep_map only caches one class with subclass == 0,
and looks up hash table of classes when subclass != 0.
It seems that this has no problem because the case of
subclass != 0 is rare. But locks of struct rq are
acquired with subclass == 1 when task migration is executed.
Task migration is high frequent event, so I modified lockdep
to cache subclasses.
I measured the score of perf bench sched messaging.
This patch has slightly but certain (order of milli seconds
or 10 milli seconds) effect when lots of tasks are running.
I'll show the result in the tail of this description.
NR_LOCKDEP_CACHING_CLASSES specifies how many classes can be
cached in the instances of lockdep_map.
I discussed with Peter Zijlstra in LinuxCon Japan about
this approach and he taught me that caching every subclasses(8)
is cleary waste of memory. So number of cached classes
should be configurable.
=== Score comparison of benchmarks ===
# "min" means best score, and "max" means worst score
for i in `seq 1 10`; do ./perf bench -f simple sched messaging; done
before: min: 0.565000, max: 0.583000, avg: 0.572500
after: min: 0.559000, max: 0.568000, avg: 0.563300
# with more processes
for i in `seq 1 10`; do ./perf bench -f simple sched messaging -g 40; done
before: min: 2.274000, max: 2.298000, avg: 2.286300
after: min: 2.242000, max: 2.270000, avg: 2.259700
Signed-off-by: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1286269311-28336-2-git-send-email-mitake@dcl.info.waseda.ac.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
For people who otherwise get to write: cpu_clock(smp_processor_id()),
there is now: local_clock().
Also, as per suggestion from Andrew, provide some documentation on
the various clock interfaces, and minimize the unsigned long long vs
u64 mess.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jens Axboe <jaxboe@fusionio.com>
LKML-Reference: <1275052414.1645.52.camel@laptop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
The conversion of device->sem to device->mutex resulted in lockdep
warnings. Create a novalidate class for now until the driver folks
come up with separate classes. That way we have at least the basic
mutex debugging coverage.
Add a checkpatch error so the usage is reserved for device->mutex.
[ tglx: checkpatch and compile fix for LOCKDEP=n ]
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
* 'perf-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (311 commits)
perf tools: Add mode to build without newt support
perf symbols: symbol inconsistency message should be done only at verbose=1
perf tui: Add explicit -lslang option
perf options: Type check all the remaining OPT_ variants
perf options: Type check OPT_BOOLEAN and fix the offenders
perf options: Check v type in OPT_U?INTEGER
perf options: Introduce OPT_UINTEGER
perf tui: Add workaround for slang < 2.1.4
perf record: Fix bug mismatch with -c option definition
perf options: Introduce OPT_U64
perf tui: Add help window to show key associations
perf tui: Make <- exit menus too
perf newt: Add single key shortcuts for zoom into DSO and threads
perf newt: Exit browser unconditionally when CTRL+C, q or Q is pressed
perf newt: Fix the 'A'/'a' shortcut for annotate
perf newt: Make <- exit the ui_browser
x86, perf: P4 PMU - fix counters management logic
perf newt: Make <- zoom out filters
perf report: Report number of events, not samples
perf hist: Clarify events_stats fields usage
...
Fix up trivial conflicts in kernel/fork.c and tools/perf/builtin-record.c
* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (24 commits)
rcu: remove all rcu head initializations, except on_stack initializations
rcu head introduce rcu head init on stack
Debugobjects transition check
rcu: fix build bug in RCU_FAST_NO_HZ builds
rcu: RCU_FAST_NO_HZ must check RCU dyntick state
rcu: make SRCU usable in modules
rcu: improve the RCU CPU-stall warning documentation
rcu: reduce the number of spurious RCU_SOFTIRQ invocations
rcu: permit discontiguous cpu_possible_mask CPU numbering
rcu: improve RCU CPU stall-warning messages
rcu: print boot-time console messages if RCU configs out of ordinary
rcu: disable CPU stall warnings upon panic
rcu: enable CPU_STALL_VERBOSE by default
rcu: slim down rcutiny by removing rcu_scheduler_active and friends
rcu: refactor RCU's context-switch handling
rcu: rename rcutiny rcu_ctrlblk to rcu_sched_ctrlblk
rcu: shrink rcutiny by making synchronize_rcu_bh() be inline
rcu: fix now-bogus rcu_scheduler_active comments.
rcu: Fix bogus CONFIG_PROVE_LOCKING in comments to reflect reality.
rcu: ignore offline CPUs in last non-dyntick-idle CPU check
...
There is no need to disable lockdep after an RCU lockdep splat,
so remove the debug_lockdeps_off() from lockdep_rcu_dereference().
To avoid repeated lockdep splats, use a static variable in the inlined
rcu_dereference_check() and rcu_dereference_protected() macros so that
a given instance splats only once, but so that multiple instances can
be detected per boot.
This is controlled by a new config variable CONFIG_PROVE_RCU_REPEATEDLY,
which is disabled by default. This provides the normal lockdep behavior
by default, but permits people who want to find multiple RCU-lockdep
splats per boot to easily do so.
Requested-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Tested-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Tejun Heo
Peter Zijlstra
Linus Torvalds
Steven Rostedt
Lucas De Marchi
Hitoshi Mitake
John Kacur
Peter Zijlstra
Lai Jiangshan
Frederic Weisbecker