[ISSUE] Memleak in LED sysfs on heavy usage

From: Daniel Gorsulowski <daniel.gorsulowski@esd.eu>
To: "linux-leds@vger.kernel.org" <linux-leds@vger.kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: [ISSUE] Memleak in LED sysfs on heavy usage
Date: Mon, 12 Sep 2016 10:50:52 +0200	[thread overview]
Message-ID: <d3cf2089-794f-f156-c5b9-ed749076c0dd@esd.eu> (raw)

Hello!

Please consider if I made something wrong, sending this issue. This is 
my first contact to the LKML.
By mistake, I accessed an LED via /sys/class/leds subsystem very fast in 
an user application. I figured out, that the free user memory decreased 
constantly. So I tried to analyze the Problem and wrote a litte script:

#!/bin/sh
while [ 1 ]; do
         echo 1 > /sys/class/leds/2a_service_yellow/brightness
         echo 0 > /sys/class/leds/2a_service_yellow/brightness
done

And voila, I was able to reproduce the problem.
So I add a bit more debugging:

#!/bin/sh
cnt=0
while [ 1 ]; do
         if [ `expr $cnt % 1000` -eq 0 ]; then
                 free | grep Mem: | cut -d' ' -f25
         fi
         echo 1 > /sys/class/leds/2a_service_yellow/brightness
         echo 0 > /sys/class/leds/2a_service_yellow/brightness
         let "cnt++"
done

And huh? No memory is eaten anymore. So it looks like, the problem only 
occours on heavy (fast) usage of /sys/class/leds subsystem.

I rewrote the script and toggled a GPIO pin, but there was no problem 
recognizable.

Some details about my test environment:
Hardware: Ti Sitara AM3357ZCZ with 128MiB memory
Kernel: vanilla 4.6

The relevant part of my .dts:
#include "am33xx.dtsi"

/ {
...
	cpus {
		cpu@0 {
			cpu0-supply = <&dcdc2_reg>;
			operating-points = <
				/* kHz    uV */
				800000  1300000
				600000  1112000
				300000   969000
			>;
		};
	};

	memory {
		device_type = "memory";
		reg = <0x80000000 0x08000000>; /* 128 Mib */
	};
...

	leds {
		pinctrl-names = "default";
		pinctrl-0 = <&user_leds_s0>;

		compatible = "gpio-leds";

...
		led2 {
			label = "2a_service_yellow";
			gpios = <&gpio1 2 GPIO_ACTIVE_HIGH>;
			linux,default-trigger = "2a_service_yellow";
			default-state = "off";
		};

...
	};
...
};

&am33xx_pinmux {
	pinctrl-names = "default";
	pinctrl-0 = <&gpio_misc_pins>;

...
	user_leds_s0: user_leds_s0 {
		pinctrl-single,pins = <
...
			0x24 (PIN_OUTPUT_PULLDOWN | MUX_MODE7) /* (T10) gpmc_ad9.gpio0[23] */
		>;
	};
...
};
...

Kind regards
Daniel