Commit ca90a7a3 authored by Jonathan Corbet's avatar Jonathan Corbet

docs: sphinxify kmemleak.txt and move it to dev-tools

Acked-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 1ead009c
Kernel Memory Leak Detector
===========================
Introduction
------------
Kmemleak provides a way of detecting possible kernel memory leaks in a
way similar to a tracing garbage collector
(https://en.wikipedia.org/wiki/Garbage_collection_%28computer_science%29#Tracing_garbage_collectors),
with the difference that the orphan objects are not freed but only
reported via /sys/kernel/debug/kmemleak. A similar method is used by the
Valgrind tool (memcheck --leak-check) to detect the memory leaks in
Valgrind tool (``memcheck --leak-check``) to detect the memory leaks in
user-space applications.
Kmemleak is supported on x86, arm, powerpc, sparc, sh, microblaze, ppc, mips, s390, metag and tile.
......@@ -19,20 +16,20 @@ Usage
CONFIG_DEBUG_KMEMLEAK in "Kernel hacking" has to be enabled. A kernel
thread scans the memory every 10 minutes (by default) and prints the
number of new unreferenced objects found. To display the details of all
the possible memory leaks:
the possible memory leaks::
# mount -t debugfs nodev /sys/kernel/debug/
# cat /sys/kernel/debug/kmemleak
To trigger an intermediate memory scan:
To trigger an intermediate memory scan::
# echo scan > /sys/kernel/debug/kmemleak
To clear the list of all current possible memory leaks:
To clear the list of all current possible memory leaks::
# echo clear > /sys/kernel/debug/kmemleak
New leaks will then come up upon reading /sys/kernel/debug/kmemleak
New leaks will then come up upon reading ``/sys/kernel/debug/kmemleak``
again.
Note that the orphan objects are listed in the order they were allocated
......@@ -40,22 +37,31 @@ and one object at the beginning of the list may cause other subsequent
objects to be reported as orphan.
Memory scanning parameters can be modified at run-time by writing to the
/sys/kernel/debug/kmemleak file. The following parameters are supported:
off - disable kmemleak (irreversible)
stack=on - enable the task stacks scanning (default)
stack=off - disable the tasks stacks scanning
scan=on - start the automatic memory scanning thread (default)
scan=off - stop the automatic memory scanning thread
scan=<secs> - set the automatic memory scanning period in seconds
(default 600, 0 to stop the automatic scanning)
scan - trigger a memory scan
clear - clear list of current memory leak suspects, done by
marking all current reported unreferenced objects grey,
or free all kmemleak objects if kmemleak has been disabled.
dump=<addr> - dump information about the object found at <addr>
Kmemleak can also be disabled at boot-time by passing "kmemleak=off" on
``/sys/kernel/debug/kmemleak`` file. The following parameters are supported:
- off
disable kmemleak (irreversible)
- stack=on
enable the task stacks scanning (default)
- stack=off
disable the tasks stacks scanning
- scan=on
start the automatic memory scanning thread (default)
- scan=off
stop the automatic memory scanning thread
- scan=<secs>
set the automatic memory scanning period in seconds
(default 600, 0 to stop the automatic scanning)
- scan
trigger a memory scan
- clear
clear list of current memory leak suspects, done by
marking all current reported unreferenced objects grey,
or free all kmemleak objects if kmemleak has been disabled.
- dump=<addr>
dump information about the object found at <addr>
Kmemleak can also be disabled at boot-time by passing ``kmemleak=off`` on
the kernel command line.
Memory may be allocated or freed before kmemleak is initialised and
......@@ -63,13 +69,14 @@ these actions are stored in an early log buffer. The size of this buffer
is configured via the CONFIG_DEBUG_KMEMLEAK_EARLY_LOG_SIZE option.
If CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF are enabled, the kmemleak is
disabled by default. Passing "kmemleak=on" on the kernel command
disabled by default. Passing ``kmemleak=on`` on the kernel command
line enables the function.
Basic Algorithm
---------------
The memory allocations via kmalloc, vmalloc, kmem_cache_alloc and
The memory allocations via :c:func:`kmalloc`, :c:func:`vmalloc`,
:c:func:`kmem_cache_alloc` and
friends are traced and the pointers, together with additional
information like size and stack trace, are stored in a rbtree.
The corresponding freeing function calls are tracked and the pointers
......@@ -113,13 +120,13 @@ when doing development. To work around these situations you can use the
you can find new unreferenced objects; this should help with testing
specific sections of code.
To test a critical section on demand with a clean kmemleak do:
To test a critical section on demand with a clean kmemleak do::
# echo clear > /sys/kernel/debug/kmemleak
... test your kernel or modules ...
# echo scan > /sys/kernel/debug/kmemleak
Then as usual to get your report with:
Then as usual to get your report with::
# cat /sys/kernel/debug/kmemleak
......@@ -131,7 +138,7 @@ disabled by the user or due to an fatal error, internal kmemleak objects
won't be freed when kmemleak is disabled, and those objects may occupy
a large part of physical memory.
In this situation, you may reclaim memory with:
In this situation, you may reclaim memory with::
# echo clear > /sys/kernel/debug/kmemleak
......@@ -140,20 +147,20 @@ Kmemleak API
See the include/linux/kmemleak.h header for the functions prototype.
kmemleak_init - initialize kmemleak
kmemleak_alloc - notify of a memory block allocation
kmemleak_alloc_percpu - notify of a percpu memory block allocation
kmemleak_free - notify of a memory block freeing
kmemleak_free_part - notify of a partial memory block freeing
kmemleak_free_percpu - notify of a percpu memory block freeing
kmemleak_update_trace - update object allocation stack trace
kmemleak_not_leak - mark an object as not a leak
kmemleak_ignore - do not scan or report an object as leak
kmemleak_scan_area - add scan areas inside a memory block
kmemleak_no_scan - do not scan a memory block
kmemleak_erase - erase an old value in a pointer variable
kmemleak_alloc_recursive - as kmemleak_alloc but checks the recursiveness
kmemleak_free_recursive - as kmemleak_free but checks the recursiveness
- ``kmemleak_init`` - initialize kmemleak
- ``kmemleak_alloc`` - notify of a memory block allocation
- ``kmemleak_alloc_percpu`` - notify of a percpu memory block allocation
- ``kmemleak_free`` - notify of a memory block freeing
- ``kmemleak_free_part`` - notify of a partial memory block freeing
- ``kmemleak_free_percpu`` - notify of a percpu memory block freeing
- ``kmemleak_update_trace`` - update object allocation stack trace
- ``kmemleak_not_leak`` - mark an object as not a leak
- ``kmemleak_ignore`` - do not scan or report an object as leak
- ``kmemleak_scan_area`` - add scan areas inside a memory block
- ``kmemleak_no_scan`` - do not scan a memory block
- ``kmemleak_erase`` - erase an old value in a pointer variable
- ``kmemleak_alloc_recursive`` - as kmemleak_alloc but checks the recursiveness
- ``kmemleak_free_recursive`` - as kmemleak_free but checks the recursiveness
Dealing with false positives/negatives
--------------------------------------
......
......@@ -20,3 +20,4 @@ whole; patches welcome!
gcov
kasan
ubsan
kmemleak
......@@ -6812,7 +6812,7 @@ F: mm/kmemcheck.c
KMEMLEAK
M: Catalin Marinas <catalin.marinas@arm.com>
S: Maintained
F: Documentation/kmemleak.txt
F: Documentation/dev-tools/kmemleak.rst
F: include/linux/kmemleak.h
F: mm/kmemleak.c
F: mm/kmemleak-test.c
......
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