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aha/lib/Kconfig.debug
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

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config PRINTK_TIME
bool "Show timing information on printks"
help
Selecting this option causes timing information to be
included in printk output. This allows you to measure
the interval between kernel operations, including bootup
operations. This is useful for identifying long delays
in kernel startup.
config MAGIC_SYSRQ
bool "Magic SysRq key"
depends on !UML
help
If you say Y here, you will have some control over the system even
if the system crashes for example during kernel debugging (e.g., you
will be able to flush the buffer cache to disk, reboot the system
immediately or dump some status information). This is accomplished
by pressing various keys while holding SysRq (Alt+PrintScreen). It
also works on a serial console (on PC hardware at least), if you
send a BREAK and then within 5 seconds a command keypress. The
keys are documented in <file:Documentation/sysrq.txt>. Don't say Y
unless you really know what this hack does.
config UNUSED_SYMBOLS
bool "Enable unused/obsolete exported symbols"
default y if X86
help
Unused but exported symbols make the kernel needlessly bigger. For
that reason most of these unused exports will soon be removed. This
option is provided temporarily to provide a transition period in case
some external kernel module needs one of these symbols anyway. If you
encounter such a case in your module, consider if you are actually
using the right API. (rationale: since nobody in the kernel is using
this in a module, there is a pretty good chance it's actually the
wrong interface to use). If you really need the symbol, please send a
mail to the linux kernel mailing list mentioning the symbol and why
you really need it, and what the merge plan to the mainline kernel for
your module is.
config DEBUG_KERNEL
bool "Kernel debugging"
help
Say Y here if you are developing drivers or trying to debug and
identify kernel problems.
config LOG_BUF_SHIFT
int "Kernel log buffer size (16 => 64KB, 17 => 128KB)" if DEBUG_KERNEL
range 12 21
default 17 if S390 || LOCKDEP
default 16 if X86_NUMAQ || IA64
default 15 if SMP
default 14
help
Select kernel log buffer size as a power of 2.
Defaults and Examples:
17 => 128 KB for S/390
16 => 64 KB for x86 NUMAQ or IA-64
15 => 32 KB for SMP
14 => 16 KB for uniprocessor
13 => 8 KB
12 => 4 KB
config DETECT_SOFTLOCKUP
bool "Detect Soft Lockups"
depends on DEBUG_KERNEL
default y
help
Say Y here to enable the kernel to detect "soft lockups",
which are bugs that cause the kernel to loop in kernel
mode for more than 10 seconds, without giving other tasks a
chance to run.
When a soft-lockup is detected, the kernel will print the
current stack trace (which you should report), but the
system will stay locked up. This feature has negligible
overhead.
(Note that "hard lockups" are separate type of bugs that
can be detected via the NMI-watchdog, on platforms that
support it.)
config SCHEDSTATS
bool "Collect scheduler statistics"
depends on DEBUG_KERNEL && PROC_FS
help
If you say Y here, additional code will be inserted into the
scheduler and related routines to collect statistics about
scheduler behavior and provide them in /proc/schedstat. These
stats may be useful for both tuning and debugging the scheduler
If you aren't debugging the scheduler or trying to tune a specific
application, you can say N to avoid the very slight overhead
this adds.
config DEBUG_SLAB
bool "Debug slab memory allocations"
depends on DEBUG_KERNEL && SLAB
help
Say Y here to have the kernel do limited verification on memory
allocation as well as poisoning memory on free to catch use of freed
memory. This can make kmalloc/kfree-intensive workloads much slower.
config DEBUG_SLAB_LEAK
bool "Memory leak debugging"
depends on DEBUG_SLAB
config DEBUG_PREEMPT
bool "Debug preemptible kernel"
depends on DEBUG_KERNEL && PREEMPT && TRACE_IRQFLAGS_SUPPORT
default y
help
If you say Y here then the kernel will use a debug variant of the
commonly used smp_processor_id() function and will print warnings
if kernel code uses it in a preemption-unsafe way. Also, the kernel
will detect preemption count underflows.
config DEBUG_RT_MUTEXES
bool "RT Mutex debugging, deadlock detection"
depends on DEBUG_KERNEL && RT_MUTEXES
help
This allows rt mutex semantics violations and rt mutex related
deadlocks (lockups) to be detected and reported automatically.
config DEBUG_PI_LIST
bool
default y
depends on DEBUG_RT_MUTEXES
config RT_MUTEX_TESTER
bool "Built-in scriptable tester for rt-mutexes"
depends on DEBUG_KERNEL && RT_MUTEXES
help
This option enables a rt-mutex tester.
config DEBUG_SPINLOCK
bool "Spinlock debugging"
depends on DEBUG_KERNEL
help
Say Y here and build SMP to catch missing spinlock initialization
and certain other kinds of spinlock errors commonly made. This is
best used in conjunction with the NMI watchdog so that spinlock
deadlocks are also debuggable.
config DEBUG_SPINLOCK_SLEEP
bool "Sleep-inside-spinlock checking"
depends on DEBUG_KERNEL
help
If you say Y here, various routines which may sleep will become very
noisy if they are called with a spinlock held.
config DEBUG_LOCKING_API_SELFTESTS
bool "Locking API boot-time self-tests"
depends on DEBUG_KERNEL
help
Say Y here if you want the kernel to run a short self-test during
bootup. The self-test checks whether common types of locking bugs
are detected by debugging mechanisms or not. (if you disable
lock debugging then those bugs wont be detected of course.)
The following locking APIs are covered: spinlocks, rwlocks,
mutexes and rwsems.
config STACKTRACE
bool
depends on STACKTRACE_SUPPORT
config DEBUG_KOBJECT
bool "kobject debugging"
depends on DEBUG_KERNEL
help
If you say Y here, some extra kobject debugging messages will be sent
to the syslog.
config DEBUG_HIGHMEM
bool "Highmem debugging"
depends on DEBUG_KERNEL && HIGHMEM
help
This options enables addition error checking for high memory systems.
Disable for production systems.
config DEBUG_BUGVERBOSE
bool "Verbose BUG() reporting (adds 70K)" if DEBUG_KERNEL && EMBEDDED
depends on BUG
depends on ARM || ARM26 || M32R || M68K || SPARC32 || SPARC64 || X86_32 || FRV
default !EMBEDDED
help
Say Y here to make BUG() panics output the file name and line number
of the BUG call as well as the EIP and oops trace. This aids
debugging but costs about 70-100K of memory.
config DEBUG_INFO
bool "Compile the kernel with debug info"
depends on DEBUG_KERNEL
help
If you say Y here the resulting kernel image will include
debugging info resulting in a larger kernel image.
Say Y here only if you plan to debug the kernel.
If unsure, say N.
config DEBUG_FS
bool "Debug Filesystem"
depends on SYSFS
help
debugfs is a virtual file system that kernel developers use to put
debugging files into. Enable this option to be able to read and
write to these files.
If unsure, say N.
config DEBUG_VM
bool "Debug VM"
depends on DEBUG_KERNEL
help
Enable this to turn on extended checks in the virtual-memory system
that may impact performance.
If unsure, say N.
config FRAME_POINTER
bool "Compile the kernel with frame pointers"
depends on DEBUG_KERNEL && (X86 || CRIS || M68K || M68KNOMMU || FRV || UML || S390)
default y if DEBUG_INFO && UML
help
If you say Y here the resulting kernel image will be slightly larger
and slower, but it might give very useful debugging information on
some architectures or if you use external debuggers.
If you don't debug the kernel, you can say N.
config UNWIND_INFO
bool "Compile the kernel with frame unwind information"
depends on !IA64 && !PARISC
depends on !MODULES || !(MIPS || PPC || SUPERH || V850)
help
If you say Y here the resulting kernel image will be slightly larger
but not slower, and it will give very useful debugging information.
If you don't debug the kernel, you can say N, but we may not be able
to solve problems without frame unwind information or frame pointers.
config STACK_UNWIND
bool "Stack unwind support"
depends on UNWIND_INFO
depends on X86
help
This enables more precise stack traces, omitting all unrelated
occurrences of pointers into kernel code from the dump.
config FORCED_INLINING
bool "Force gcc to inline functions marked 'inline'"
depends on DEBUG_KERNEL
default y
help
This option determines if the kernel forces gcc to inline the functions
developers have marked 'inline'. Doing so takes away freedom from gcc to
do what it thinks is best, which is desirable for the gcc 3.x series of
compilers. The gcc 4.x series have a rewritten inlining algorithm and
disabling this option will generate a smaller kernel there. Hopefully
this algorithm is so good that allowing gcc4 to make the decision can
become the default in the future, until then this option is there to
test gcc for this.
config RCU_TORTURE_TEST
tristate "torture tests for RCU"
depends on DEBUG_KERNEL
default n
help
This option provides a kernel module that runs torture tests
on the RCU infrastructure. The kernel module may be built
after the fact on the running kernel to be tested, if desired.
Say Y here if you want RCU torture tests to start automatically
at boot time (you probably don't).
Say M if you want the RCU torture tests to build as a module.
Say N if you are unsure.
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