Kmemleak

Applicable for

1. Article purpose[edit source]

This article provides the basic information needed to start using the Linux kernel tool: kmemleak^[1].

2. Introduction[edit source]

The following table provides a brief description of the tool, as well as its availability depending on the software packages:

: this tool is either present (ready to use or to be activated), or can be integrated and activated on the software package.

: this tool is not present and cannot be integrated, or it is present but cannot be activated on the software package.

Tool

STM32MPU Embedded Software distribution

STM32MPU Embedded Software distribution for Android™

Warning

STM32MPU Embedded Software distribution for Android™ is no more supported by ST. You can contact our ST partner, Witekio, who can help you to port and maintain it on STM32MP15 platform.

Name

3. Installing the trace and debug tool on your target board[edit source]

In order to use kmemleak, the Linux kernel configuration must activate CONFIG_DEBUG_KMEMLEAK:

Symbol: DEBUG_KMEMLEAK
Location:
  Kernel Hacking --->
    Memory Debugging -->
      [*] Kernel memory leak detector

3.1. Using STM32MPU Embedded Software Distribution[edit source]

3.1.1. Developer Package[edit source]

To enable CONFIG_DEBUG_KMEMLEAK in the Linux kernel configuration, please refer to the Menuconfig or how to configure kernel article to find instructions for modification of the configuration and recompiling Linux kernel image in Developer Package context.

3.1.2. Distribution Package[edit source]

To enable CONFIG_DEBUG_KMEMLEAK in the Linux kernel configuration, please refer to the Menuconfig or how to configure kernel article to find instructions for modifying the configuration and recompiling the Linux kernel image in the Distribution Package context.

3.2. Using STM32MPU Embedded Software Distribution for Android™[edit source]

3.2.1. Distribution Package[edit source]

Warning

STM32MPU Embedded Software distribution for Android™ is no more supported by ST. You can contact our ST partner, Witekio, who can help you to port and maintain it on STM32MP15 platform.

4. Getting started[edit source]

Below information is related to the Android™ distribution
Need to enable root access rights

Using ADB shell is ADB link available:

 adb root
 adb shell
 ...

Using uart console shell:

 su
 ...

4.1. Reading kmemleak report[edit source]

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:

 cat /sys/kernel/debug/kmemleak

Note: debugfs is mounted by default, otherwise you can mount it using the following command. Please refer to the Debugfs article.

Kmemleak result example: contains an extract of the memory content, and backtrace of function calls, to help you when debugging.

unreferenced object 0xed638800 (size 64):
  comm "swapper/0", pid 1, jiffies 4294937542 (age 197.490s)
  hex dump (first 32 bytes):
    01 00 00 00 77 f9 ff 7a cf 37 dd e3 01 00 00 00  ....w..z.7......
    00 92 63 ed 40 00 00 00 00 00 00 00 01 00 00 00  ..c.@...........
  backtrace:
    [<c048d130>] pinconf_generic_parse_dt_config+0x10c/0x13c
    [<c0490f88>] stm32_pctrl_dt_node_to_map+0x90/0x3f4
    [<c048ca58>] pinctrl_dt_to_map+0x130/0x35c
    [<c04895a0>] create_pinctrl+0x60/0x3b0
    [<c0489a08>] devm_pinctrl_get+0x38/0x68
    [<c0582a24>] pinctrl_bind_pins+0x48/0x280
    [<c055f7f8>] driver_probe_device+0xc0/0x470
    [<c055fca8>] __driver_attach+0x100/0x11c
    [<c055db08>] bus_for_each_dev+0x4c/0x9c
    [<c055ecc4>] bus_add_driver+0x1c0/0x264
    [<c0560910>] driver_register+0x78/0xf4
    [<c0101c48>] do_one_initcall+0x44/0x168
    [<c0f00e74>] kernel_init_freeable+0x1c0/0x24c
    [<c0a65ac4>] kernel_init+0x8/0x110
    [<c0108b50>] ret_from_fork+0x14/0x24
    [<ffffffff>] 0xffffffff

4.2. Trigerring an intermediate memory scan[edit source]

 echo scan > /sys/kernel/debug/kmemleak

4.3. Clearing the list of all current possible memory leaks[edit source]

 echo clear > /sys/kernel/debug/kmemleak

4.4. All kmemleak commands[edit source]

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 in grey, or freeing all kmemleak objects if kmemleak is disabled.
dump=<addr> - dump information about the object found at <addr>

5. To go further[edit source]

If enabled in the Linux kernel configuration, Kmemleak can also be disabled at boot time by passing kmemleak=off on the kernel command line.

Conversely, if CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF is enabled in the Linux kernel configuration, kmemleak is disabled by default.

Symbol: DEBUG_KMEMLEAK_DEFAULT_OFF
Location:
  Kernel Hacking --->
    Memory Debugging -->
      [*] Kernel memory leak detector
        [*] Default kmemleak to off

Passing kmemleak=on on the kernel command line enables the function.

6. References[edit source]

↑ ^1.0 ^1.1 http://www.procode.org/kmemleak/

Useful external links

Document link	Document Type	Description
Kernel Memory Leak Detector	Standard	Documentation from kernel.org

[procodedotorg-1] 1.0 ^1.1 http://www.procode.org/kmemleak/

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