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Introduction

• Kmemleak is a Linux kernel feature designed to detect and report memory leaks in the kernel code. Memory leaks occur when a program allocates memory dynamically but fails to release it when it is no longer needed. This can result in a gradual loss of memory over time, eventually leading to system instability or even crashes.
• Kmemleak works by scanning the kernel memory periodically to detect any memory that has been allocated but not freed. When it detects a potential memory leak, it reports it to the system log along with a stack trace that shows where the memory was allocated. This information can help developers to identify and fix the source of the memory leak.
• Kmemleak is a useful tool for kernel developers and system administrators who want to ensure that their systems are stable and free of memory leaks. It can be enabled in the kernel configuration, and once enabled, it will run automatically in the background, periodically scanning the kernel memory for leaks.

Required kernel configs need to enable

CONFIG_HAVE_DEBUG_KMEMLEAK=y
CONFIG_DEBUG_KMEMLEAK=y
CONFIG_DEBUG_KMEMLEAK_TEST=m

Integrating Kmemleak tool  for RPI-3

1) Create kmemleak.cfg file under meta-cmf-raspberrypi/recipes-kernel/linux/files with below kernel configs.
Note: Need to add this change in corresponding platform OEM layer.

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5) Once enabled kmemleak we will get kernel memory leaks in /sys/kernel/debug/kmemleak file if leaks are reported.

Testing kmemleak tool with kmemleak-test module in RPI-3

kmemleak-test is a test module available as part of kmemleak. By default, this module is not compiled in RPI3 and so there is no kmemleak-test.ko module. If needed, we need to enable to build as a module by following the above mentioned kernel configurations.
Path of kmemleak-test module source : build-raspberrypi-rdk-mc/tmp/work-shared/raspberrypi-rdk-mc/kernel-source/samples/kmemleak/kmemleak-test.c
kmemleak-test.ko

Note: Need to generate kmemleak-test.ko module file from corresponding platform specific kernel source code.

Step 1 : Copy kmemleak-test.ko module to this path /lib/modules/5.10.52-v7/  in box .
Step 2 : load the module to kernel space with insmod command.
Ex:

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Testing memory leaks from your kernel code

Suppose that you have a kernel module code which you want to test for kernel memory leaks. Make sure that kmemleak is enabled as mentioned above. Then, run the functionality of your kernel module by invoking it. Any memory leaks present in the kernel driver code will be reported in /sys/kernel/debug/kmemleak.

Memory leaks from module_init and module_exit functions get reported when the driver is inserted or removed. Inorder to test  the memory leaks present in other functions , we need to manually invoke those functions. 

Limitations and Drawbacks

While kmemleak can be a useful tool for detecting and reporting memory leaks in the Linux kernel, there are several limitations and drawbacks to consider:
The main drawback is the reduced performance of memory allocation and freeing. To avoid other penalties, the memory scanning is only performed when the /sys/kernel/debug/kmemleak file is read. Anyway, this tool is intended for debugging purposes where the performance might not be the most important requirement.

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