lib/Kconfig.debug v3.0-rc7


Show timing information on printks

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.  Or add printk.time=1 at boot-time.
See Documentation/kernel-parameters.txt


Default message log level (1-7)

Default log level for printk statements with no specified priority.

This was hard-coded to KERN_WARNING since at least 2.6.10 but folks
that are auditing their logs closely may want to set it to a lower


Enable __deprecated logic

Enable the __deprecated logic in the kernel build.
Disable this to suppress the "warning: 'foo' is deprecated
(declared at kernel/power/somefile.c:1234)" messages.


Enable __must_check logic

Enable the __must_check logic in the kernel build.  Disable this to
suppress the "warning: ignoring return value of 'foo', declared with
attribute warn_unused_result" messages.


Warn for stack frames larger than (needs gcc 4.4)

Tell gcc to warn at build time for stack frames larger than this.
Setting this too low will cause a lot of warnings.
Setting it to 0 disables the warning.
Requires gcc 4.4


Magic SysRq key

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.


Strip assembler-generated symbols during link

Strip internal assembler-generated symbols during a link (symbols
that look like '.Lxxx') so they don't pollute the output of
get_wchan() and suchlike.


Enable unused/obsolete exported symbols

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.


Debug Filesystem

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.

For detailed documentation on the debugfs API, see

If unsure, say N.


Run 'make headers_check' when building vmlinux

This option will extract the user-visible kernel headers whenever
building the kernel, and will run basic sanity checks on them to
ensure that exported files do not attempt to include files which
were not exported, etc.

If you're making modifications to header files which are
relevant for userspace, say 'Y', and check the headers
exported to $(INSTALL_HDR_PATH) (usually 'usr/include' in
your build tree), to make sure they're suitable.


Enable full Section mismatch analysis

The section mismatch analysis checks if there are illegal
references from one section to another section.
Linux will during link or during runtime drop some sections
and any use of code/data previously in these sections will
most likely result in an oops.
In the code functions and variables are annotated with
__init, __devinit etc. (see full list in include/linux/init.h)
which results in the code/data being placed in specific sections.
The section mismatch analysis is always done after a full
kernel build but enabling this option will in addition
do the following:
- Add the option -fno-inline-functions-called-once to gcc
When inlining a function annotated __init in a non-init
function we would lose the section information and thus
the analysis would not catch the illegal reference.
This option tells gcc to inline less but will also
result in a larger kernel.
- Run the section mismatch analysis for each module/built-in.o
When we run the section mismatch analysis on vmlinux.o we
lose valueble information about where the mismatch was
Running the analysis for each module/built-in.o file
will tell where the mismatch happens much closer to the
source. The drawback is that we will report the same
mismatch at least twice.
- Enable verbose reporting from modpost to help solving
the section mismatches reported.


Kernel debugging

Say Y here if you are developing drivers or trying to debug and
identify kernel problems.


Debug shared IRQ handlers

Enable this to generate a spurious interrupt as soon as a shared
interrupt handler is registered, and just before one is deregistered.
Drivers ought to be able to handle interrupts coming in at those
points; some don't and need to be caught.


Detect Hard and Soft Lockups

Say Y here to enable the kernel to act as a watchdog to detect
hard and soft lockups.

Softlockups are bugs that cause the kernel to loop in kernel
mode for more than 60 seconds, without giving other tasks a
chance to run.  The current stack trace is displayed upon
detection and the system will stay locked up.

Hardlockups are bugs that cause the CPU to loop in kernel mode
for more than 60 seconds, without letting other interrupts have a
chance to run.  The current stack trace is displayed upon detection
and the system will stay locked up.

The overhead should be minimal.  A periodic hrtimer runs to
generate interrupts and kick the watchdog task every 10-12 seconds.
An NMI is generated every 60 seconds or so to check for hardlockups.


Panic (Reboot) On Hard Lockups

Say Y here to enable the kernel to panic on "hard lockups",
which are bugs that cause the kernel to loop in kernel
mode with interrupts disabled for more than 60 seconds.

Say N if unsure.


Panic (Reboot) On Soft Lockups

Say Y here to enable the kernel to panic on "soft lockups",
which are bugs that cause the kernel to loop in kernel
mode for more than 60 seconds, without giving other tasks a
chance to run.

The panic can be used in combination with panic_timeout,
to cause the system to reboot automatically after a
lockup has been detected. This feature is useful for
high-availability systems that have uptime guarantees and
where a lockup must be resolved ASAP.

Say N if unsure.


Detect Hung Tasks

Say Y here to enable the kernel to detect "hung tasks",
which are bugs that cause the task to be stuck in
uninterruptible "D" state indefinitiley.

When a hung task is detected, the kernel will print the
current stack trace (which you should report), but the
task will stay in uninterruptible state. If lockdep is
enabled then all held locks will also be reported. This
feature has negligible overhead.


Default timeout for hung task detection (in seconds)

This option controls the default timeout (in seconds) used
to determine when a task has become non-responsive and should
be considered hung.

It can be adjusted at runtime via the kernel.hung_task_timeout
sysctl or by writing a value to /proc/sys/kernel/hung_task_timeout.

A timeout of 0 disables the check.  The default is two minutes.
Keeping the default should be fine in most cases.


Panic (Reboot) On Hung Tasks

Say Y here to enable the kernel to panic on "hung tasks",
which are bugs that cause the kernel to leave a task stuck
in uninterruptible "D" state.

The panic can be used in combination with panic_timeout,
to cause the system to reboot automatically after a
hung task has been detected. This feature is useful for
high-availability systems that have uptime guarantees and
where a hung tasks must be resolved ASAP.

Say N if unsure.


Collect scheduler debugging info

If you say Y here, the /proc/sched_debug file will be provided
that can help debug the scheduler. The runtime overhead of this
option is minimal.


Collect scheduler statistics

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.


Collect kernel timers statistics

If you say Y here, additional code will be inserted into the
timer routines to collect statistics about kernel timers being
reprogrammed. The statistics can be read from /proc/timer_stats.
The statistics collection is started by writing 1 to /proc/timer_stats,
writing 0 stops it. This feature is useful to collect information
about timer usage patterns in kernel and userspace. This feature
is lightweight if enabled in the kernel config but not activated
(it defaults to deactivated on bootup and will only be activated
if some application like powertop activates it explicitly).


Debug object operations

If you say Y here, additional code will be inserted into the
kernel to track the life time of various objects and validate
the operations on those objects.


Debug objects selftest

This enables the selftest of the object debug code.


Debug objects in freed memory

This enables checks whether a k/v free operation frees an area
which contains an object which has not been deactivated
properly. This can make kmalloc/kfree-intensive workloads
much slower.


Debug timer objects

If you say Y here, additional code will be inserted into the
timer routines to track the life time of timer objects and
validate the timer operations.


Debug work objects

If you say Y here, additional code will be inserted into the
work queue routines to track the life time of work objects and
validate the work operations.


Debug RCU callbacks objects

Enable this to turn on debugging of RCU list heads (call_rcu() usage).


Debug percpu counter objects

If you say Y here, additional code will be inserted into the
percpu counter routines to track the life time of percpu counter
objects and validate the percpu counter operations.


debug_objects bootup default value (0-1)

Debug objects boot parameter default value


Debug slab memory allocations

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.


SLUB debugging on by default

Boot with debugging on by default. SLUB boots by default with
the runtime debug capabilities switched off. Enabling this is
equivalent to specifying the "slub_debug" parameter on boot.
There is no support for more fine grained debug control like
possible with slub_debug=xxx. SLUB debugging may be switched
off in a kernel built with CONFIG_SLUB_DEBUG_ON by specifying


Enable SLUB performance statistics

SLUB statistics are useful to debug SLUBs allocation behavior in
order find ways to optimize the allocator. This should never be
enabled for production use since keeping statistics slows down
the allocator by a few percentage points. The slabinfo command
supports the determination of the most active slabs to figure
out which slabs are relevant to a particular load.
Try running: slabinfo -DA


Kernel memory leak detector

Say Y here if you want to enable the memory leak
detector. The memory allocation/freeing is traced in a way
similar to the Boehm's conservative garbage collector, the
difference being that the orphan objects are not freed but
only shown in /sys/kernel/debug/kmemleak. Enabling this
feature will introduce an overhead to memory
allocations. See Documentation/kmemleak.txt for more

Enabling DEBUG_SLAB or SLUB_DEBUG may increase the chances
of finding leaks due to the slab objects poisoning.

In order to access the kmemleak file, debugfs needs to be
mounted (usually at /sys/kernel/debug).


Maximum kmemleak early log entries

Kmemleak must track all the memory allocations to avoid
reporting false positives. Since memory may be allocated or
freed before kmemleak is initialised, an early log buffer is
used to store these actions. If kmemleak reports "early log
buffer exceeded", please increase this value.


Simple test for the kernel memory leak detector

This option enables a module that explicitly leaks memory.

If unsure, say N.


Default kmemleak to off

Say Y here to disable kmemleak by default. It can then be enabled
on the command line via kmemleak=on.


Debug preemptible kernel

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.


RT Mutex debugging, deadlock detection

This allows rt mutex semantics violations and rt mutex related
deadlocks (lockups) to be detected and reported automatically.


Built-in scriptable tester for rt-mutexes

This option enables a rt-mutex tester.


Spinlock and rw-lock debugging: basic checks

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.


Mutex debugging: basic checks

This feature allows mutex semantics violations to be detected and


Lock debugging: detect incorrect freeing of live locks

This feature will check whether any held lock (spinlock, rwlock,
mutex or rwsem) is incorrectly freed by the kernel, via any of the
memory-freeing routines (kfree(), kmem_cache_free(), free_pages(),
vfree(), etc.), whether a live lock is incorrectly reinitialized via
spin_lock_init()/mutex_init()/etc., or whether there is any lock
held during task exit.


Lock debugging: prove locking correctness

This feature enables the kernel to prove that all locking
that occurs in the kernel runtime is mathematically
correct: that under no circumstance could an arbitrary (and
not yet triggered) combination of observed locking
sequences (on an arbitrary number of CPUs, running an
arbitrary number of tasks and interrupt contexts) cause a

In short, this feature enables the kernel to report locking
related deadlocks before they actually occur.

The proof does not depend on how hard and complex a
deadlock scenario would be to trigger: how many
participant CPUs, tasks and irq-contexts would be needed
for it to trigger. The proof also does not depend on
timing: if a race and a resulting deadlock is possible
theoretically (no matter how unlikely the race scenario
is), it will be proven so and will immediately be
reported by the kernel (once the event is observed that
makes the deadlock theoretically possible).

If a deadlock is impossible (i.e. the locking rules, as
observed by the kernel, are mathematically correct), the
kernel reports nothing.

NOTE: this feature can also be enabled for rwlocks, mutexes
and rwsems - in which case all dependencies between these
different locking variants are observed and mapped too, and
the proof of observed correctness is also maintained for an
arbitrary combination of these separate locking variants.

For more details, see Documentation/lockdep-design.txt.


RCU debugging: prove RCU correctness

This feature enables lockdep extensions that check for correct
use of RCU APIs.  This is currently under development.  Say Y
if you want to debug RCU usage or help work on the PROVE_RCU

Say N if you are unsure.


RCU debugging: don't disable PROVE_RCU on first splat

By itself, PROVE_RCU will disable checking upon issuing the
first warning (or "splat").  This feature prevents such
disabling, allowing multiple RCU-lockdep warnings to be printed
on a single reboot.

Say Y to allow multiple RCU-lockdep warnings per boot.

Say N if you are unsure.


RCU debugging: sparse-based checks for pointer usage

This feature enables the __rcu sparse annotation for
RCU-protected pointers.  This annotation will cause sparse
to flag any non-RCU used of annotated pointers.  This can be
helpful when debugging RCU usage.  Please note that this feature
is not intended to enforce code cleanliness; it is instead merely
a debugging aid.

Say Y to make sparse flag questionable use of RCU-protected pointers

Say N if you are unsure.


Lock usage statistics

This feature enables tracking lock contention points

For more details, see Documentation/lockstat.txt

This also enables lock events required by "perf lock",
subcommand of perf.
If you want to use "perf lock", you also need to turn on

CONFIG_LOCK_STAT defines "contended" and "acquired" lock events.
(CONFIG_LOCKDEP defines "acquire" and "release" events.)


Lock dependency engine debugging

If you say Y here, the lock dependency engine will do
additional runtime checks to debug itself, at the price
of more runtime overhead.


Enables hooks to interrupt enabling and disabling for
either tracing or lock debugging.


Spinlock debugging: sleep-inside-spinlock checking

If you say Y here, various routines which may sleep will become very
noisy if they are called with a spinlock held.


Locking API boot-time self-tests

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.


Stack utilization instrumentation

Enables the display of the minimum amount of free stack which each
task has ever had available in the sysrq-T and sysrq-P debug output.

This option will slow down process creation somewhat.


kobject debugging

If you say Y here, some extra kobject debugging messages will be sent
to the syslog.


Highmem debugging

This options enables addition error checking for high memory systems.
Disable for production systems.


Verbose BUG() reporting (adds 70K)

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.


Compile the kernel with debug info

If you say Y here the resulting kernel image will include
debugging info resulting in a larger kernel image.
This adds debug symbols to the kernel and modules (gcc -g), and
is needed if you intend to use kernel crashdump or binary object
tools like crash, kgdb, LKCD, gdb, etc on the kernel.
Say Y here only if you plan to debug the kernel.

If unsure, say N.


Reduce debugging information

If you say Y here gcc is instructed to generate less debugging
information for structure types. This means that tools that
need full debugging information (like kgdb or systemtap) won't
be happy. But if you merely need debugging information to
resolve line numbers there is no loss. Advantage is that
build directory object sizes shrink dramatically over a full
DEBUG_INFO build and compile times are reduced too.
Only works with newer gcc versions.


Debug VM

Enable this to turn on extended checks in the virtual-memory system
that may impact performance.

If unsure, say N.


Debug VM translations

Enable some costly sanity checks in virtual to page code. This can
catch mistakes with virt_to_page() and friends.

If unsure, say N.


Debug the global anon/private NOMMU mapping region tree

This option causes the global tree of anonymous and private mapping
regions to be regularly checked for invalid topology.


Debug filesystem writers count

Enable this to catch wrong use of the writers count in struct
vfsmount.  This will increase the size of each file struct by
32 bits.

If unsure, say N.


Debug memory initialisation

Enable this for additional checks during memory initialisation.
The sanity checks verify aspects of the VM such as the memory model
and other information provided by the architecture. Verbose
information will be printed at KERN_DEBUG loglevel depending
on the mminit_loglevel= command-line option.

If unsure, say Y


Debug linked list manipulation

Enable this to turn on extended checks in the linked-list
walking routines.

If unsure, say N.


Linked list sorting test

Enable this to turn on 'list_sort()' function test. This test is
executed only once during system boot, so affects only boot time.

If unsure, say N.


Debug SG table operations

Enable this to turn on checks on scatter-gather tables. This can
help find problems with drivers that do not properly initialize
their sg tables.

If unsure, say N.


Debug notifier call chains

Enable this to turn on sanity checking for notifier call chains.
This is most useful for kernel developers to make sure that
modules properly unregister themselves from notifier chains.
This is a relatively cheap check but if you care about maximum
performance, say N.


Debug credential management

Enable this to turn on some debug checking for credential
management.  The additional code keeps track of the number of
pointers from task_structs to any given cred struct, and checks to
see that this number never exceeds the usage count of the cred

Furthermore, if SELinux is enabled, this also checks that the
security pointer in the cred struct is never seen to be invalid.

If unsure, say N.



Compile the kernel with frame pointers

If you say Y here the resulting kernel image will be slightly
larger and slower, but it gives very useful debugging information
in case of kernel bugs. (precise oopses/stacktraces/warnings)


Delay each boot printk message by N milliseconds

This build option allows you to read kernel boot messages
by inserting a short delay after each one.  The delay is
specified in milliseconds on the kernel command line,
using "boot_delay=N".

It is likely that you would also need to use "lpj=M" to preset
the "loops per jiffie" value.
See a previous boot log for the "lpj" value to use for your
system, and then set "lpj=M" before setting "boot_delay=N".
NOTE:  Using this option may adversely affect SMP systems.
I.e., processors other than the first one may not boot up.
what it believes to be lockup conditions.


torture tests for RCU

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 be built into
the kernel.
Say M if you want the RCU torture tests to build as a module.
Say N if you are unsure.


torture tests for RCU runnable by default

This option provides a way to build the RCU torture tests
directly into the kernel without them starting up at boot
time.  You can use /proc/sys/kernel/rcutorture_runnable
to manually override this setting.  This /proc file is
available only when the RCU torture tests have been built
into the kernel.

Say Y here if you want the RCU torture tests to start during
boot (you probably don't).
Say N here if you want the RCU torture tests to start only
after being manually enabled via /proc.


RCU CPU stall timeout in seconds

If a given RCU grace period extends more than the specified
number of seconds, a CPU stall warning is printed.  If the
RCU grace period persists, additional CPU stall warnings are
printed at more widely spaced intervals.


Print additional per-task information for RCU_CPU_STALL_DETECTOR

This option causes RCU to printk detailed per-task information
for any tasks that are stalling the current RCU grace period.

Say N if you are unsure.

Say Y if you want to enable such checks.


Kprobes sanity tests

This option provides for testing basic kprobes functionality on
boot. A sample kprobe, jprobe and kretprobe are inserted and
verified for functionality.

Say N if you are unsure.


Self test for the backtrace code

This option provides a kernel module that can be used to test
the kernel stack backtrace code. This option is not useful
for distributions or general kernels, but only for kernel
developers working on architecture code.

Note that if you want to also test saved backtraces, you will
have to enable STACKTRACE as well.

Say N if you are unsure.


Force extended block device numbers and spread them

YOU ARE DOING.  Distros, please enable this and fix whatever
is broken.

Conventionally, block device numbers are allocated from
predetermined contiguous area.  However, extended block area
may introduce non-contiguous block device numbers.  This
option forces most block device numbers to be allocated from
the extended space and spreads them to discover kernel or
userland code paths which assume predetermined contiguous
device number allocation.

Note that turning on this debug option shuffles all the
device numbers for all IDE and SCSI devices including libata
ones, so root partition specified using device number
directly (via rdev or root=MAJ:MIN) won't work anymore.
Textual device names (root=/dev/sdXn) will continue to work.

Say N if you are unsure.


Force weak per-cpu definitions

s390 and alpha require percpu variables in modules to be
defined weak to work around addressing range issue which
puts the following two restrictions on percpu variable

1. percpu symbols must be unique whether static or not
2. percpu variables can't be defined inside a function

To ensure that generic code follows the above rules, this
option forces all percpu variables to be defined as weak.


Debug access to per_cpu maps

Say Y to verify that the per_cpu map being accessed has
been set up. This adds a fair amount of code to kernel memory
and decreases performance.

Say N if unsure.


Linux Kernel Dump Test Tool Module

This module enables testing of the different dumping mechanisms by
inducing system failures at predefined crash points.
If you don't need it: say N
Choose M here to compile this code as a module. The module will be
called lkdtm.

Documentation on how to use the module can be found in


CPU notifier error injection module

This option provides a kernel module that can be used to test
the error handling of the cpu notifiers

To compile this code as a module, choose M here: the module will
be called cpu-notifier-error-inject.

If unsure, say N.


Fault-injection framework

Provide fault-injection framework.
For more details, see Documentation/fault-injection/.


Fault-injection capability for kmalloc

Provide fault-injection capability for kmalloc.


Fault-injection capabilitiy for alloc_pages()

Provide fault-injection capability for alloc_pages().


Fault-injection capability for disk IO

Provide fault-injection capability for disk IO.


Fault-injection capability for faking disk interrupts

Provide fault-injection capability on end IO handling. This
will make the block layer "forget" an interrupt as configured,
thus exercising the error handling.

Only works with drivers that use the generic timeout handling,
for others it wont do anything.


Debugfs entries for fault-injection capabilities

Enable configuration of fault-injection capabilities via debugfs.


stacktrace filter for fault-injection capabilities

Provide stacktrace filter for fault-injection capabilities


Latency measuring infrastructure

Enable this option if you want to use the LatencyTOP tool
to find out which userspace is blocking on what kernel operations.


Sysctl checks

sys_sysctl uses binary paths that have been found challenging
to properly maintain and use. This enables checks that help
you to keep things correct.




Remote debugging over FireWire early on boot

If you want to debug problems which hang or crash the kernel early
on boot and the crashing machine has a FireWire port, you can use
this feature to remotely access the memory of the crashed machine
over FireWire. This employs remote DMA as part of the OHCI1394
specification which is now the standard for FireWire controllers.

With remote DMA, you can monitor the printk buffer remotely using
firescope and access all memory below 4GB using fireproxy from gdb.
Even controlling a kernel debugger is possible using remote DMA.


If ohci1394_dma=early is used as boot parameter, it will initialize
all OHCI1394 controllers which are found in the PCI config space.

As all changes to the FireWire bus such as enabling and disabling
devices cause a bus reset and thereby disable remote DMA for all
devices, be sure to have the cable plugged and FireWire enabled on
the debugging host before booting the debug target for debugging.

This code (~1k) is freed after boot. By then, the firewire stack
in charge of the OHCI-1394 controllers should be used instead.

See Documentation/debugging-via-ohci1394.txt for more information.


Remote debugging over FireWire with firewire-ohci

This option lets you use the FireWire bus for remote debugging
with help of the firewire-ohci driver. It enables unfiltered
remote DMA in firewire-ohci.
See Documentation/debugging-via-ohci1394.txt for more information.

If unsure, say N.


Build targets in Documentation/ tree

This option attempts to build objects from the source files in the
kernel Documentation/ tree.

Say N if you are unsure.


Enable dynamic printk() support

Compiles debug level messages into the kernel, which would not
otherwise be available at runtime. These messages can then be
enabled/disabled based on various levels of scope - per source file,
function, module, format string, and line number. This mechanism
implicitly enables all pr_debug() and dev_dbg() calls. The impact of
this compile option is a larger kernel text size of about 2%.


Dynamic debugging is controlled via the 'dynamic_debug/control' file,
which is contained in the 'debugfs' filesystem. Thus, the debugfs
filesystem must first be mounted before making use of this feature.
We refer the control file as: <debugfs>/dynamic_debug/control. This
file contains a list of the debug statements that can be enabled. The
format for each line of the file is:

filename:lineno [module]function flags format

filename : source file of the debug statement
lineno : line number of the debug statement
module : module that contains the debug statement
function : function that contains the debug statement
flags : 'p' means the line is turned 'on' for printing
format : the format used for the debug statement

From a live system:

nullarbor:~ # cat <debugfs>/dynamic_debug/control
# filename:lineno [module]function flags format
fs/aio.c:222 [aio]__put_ioctx - "__put_ioctx:\040freeing\040%p\012"
fs/aio.c:248 [aio]ioctx_alloc - "ENOMEM:\040nr_events\040too\040high\012"
fs/aio.c:1770 [aio]sys_io_cancel - "calling\040cancel\012"

Example usage:

// enable the message at line 1603 of file svcsock.c
nullarbor:~ # echo -n 'file svcsock.c line 1603 +p' >

// enable all the messages in file svcsock.c
nullarbor:~ # echo -n 'file svcsock.c +p' >

// enable all the messages in the NFS server module
nullarbor:~ # echo -n 'module nfsd +p' >

// enable all 12 messages in the function svc_process()
nullarbor:~ # echo -n 'func svc_process +p' >

// disable all 12 messages in the function svc_process()
nullarbor:~ # echo -n 'func svc_process -p' >

See Documentation/dynamic-debug-howto.txt for additional information.


Enable debugging of DMA-API usage

Enable this option to debug the use of the DMA API by device drivers.
With this option you will be able to detect common bugs in device
drivers like double-freeing of DMA mappings or freeing mappings that
were never allocated.
This option causes a performance degredation.  Use only if you want
to debug device drivers. If unsure, say N.


Perform an atomic64_t self-test at boot

Enable this option to test the atomic64_t functions at boot.

If unsure, say N.


Self test for hardware accelerated raid6 recovery

This is a one-shot self test that permutes through the
recovery of all the possible two disk failure scenarios for a
N-disk array.  Recovery is performed with the asynchronous
raid6 recovery routines, and will optionally use an offload
engine if one is available.

If unsure, say N.