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™ | ||||||
|---|---|---|---|---|---|---|---|---|
| Name | Category | Purpose | Starter Package | Developer Package | Distribution Package | Starter Package | Developer Package | Distribution Package |
| kmemleak | Monitoring tools | kmemleak[1] provides a means to detect possible kernel memory leaks in a similar way to a tracing garbage collector, with the difference that the orphan objects are not freed, but only reported via /sys/kernel/debug/kmemleak. | |
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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
For ecosystem release ≥ v2.0.0 
:
In this ecosystem release, this is possible to enable/disable automatic kmemleak scan at boot up.
This configuration is activated by default when DEBUG_KMEMLEAK configuration is set.
Symbol: DEBUG_KMEMLEAK_AUTO_SCAN
Location:
Kernel Hacking --->
Memory Debugging -->
[*] Kernel memory leak detector
Enable kmemleak auto scan thread on boot up
For ecosystem release ≤ v1.1.0 :
Since memory may be allocated or freed before kmemleak is initialised, an early log buffer is used to store these actions.
In this ecosystem release, the default buffer size is limited, and this is recommended to increase it.
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]
To enable CONFIG_DEBUG_KMEMLEAK in the Linux kernel configuration, please refer to the How to customize kernel for Android article to find instructions for modification of the configuration and recompiling Linux kernel image in Distribution Package context.
4. Getting started[edit source]
|
Below information is related to the Android™ distribution Need to enable root access rights
adb root adb 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]
- Useful external links
| Document link | Document Type | Description |
|---|---|---|
| Kernel Memory Leak Detector | Standard | Documentation from kernel.org |