August 2015 - kernelnewbies@kernelnewbies.org

SLUB vs SLAB allocator
by Navin Parakkal Aug. 27, 2015

Aug. 27, 2015

Hi, I found that in many worst case scenarios like fragmention of allocator , slub performs well than slab. I also noticed that Centos /Ubuntu etc switched to SLUB but SLES still uses SLAB in the default image. Any particular reason where SLAB is the choice ? I ask this since i find SLUB to be the default choice since 2.6.23 as per https://en.wikipedia.org/wiki/SLUB_(software) Regards, Navin

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Planning to write a patch
by Umair Khan Aug. 26, 2015

Aug. 26, 2015

Hello everyone, I've been thinking of writing a patch a lot lately. But with my level of knowledge I cannot do something groundbreaking. One thing which came to my mind is to write a patch related to the driver which controls the brightness of the display. What happens now is I lower down the brightness, and when I restart the laptop, it's back to the highest amount. I'm using Ubuntu 14.04 LTS on top of Linux Kernel 4.2 rc3+. I was thinking of writing the current brightness to sysfs and read that value when the driver is started during the boot. So, my question is that is it already implemented in the driver and just that Ubuntu resets it on every reboot from userspace ? And if it is not implemented, is it worth implementing ? Thanks Umair Delhi, India

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module debugging
by Salam Farhat Aug. 25, 2015

Aug. 25, 2015

Hi, I am not sure if this is the place to ask, if so please let me know where to do so. I am using a kernel module that I modified slightly to work on my current kernel version. It is running on a virtual machine and on a heavy load it goes into an infinite loop and freezes the system. I can tell that the virtual machine is using 100% of its assigned cpu. There are print statements almost everywhere in the module, but after a few seconds none get printed. The kernel has the following options already enabled: CONFIG_DETECT_SOFTLOCKUP and CONFIG_DETECT_HUNG_TASK. To my understanding the kernel is supposed to print the stack trace when a hung task is detected, however, nothing gets printed in kern.log. I am not sure if this is the place where the kernel would dump the stack or if the print process is affected by the hang since the print statements in the module are not being printed as well. I would like to know how to debug this issue. Any help is appreciated. Thank you.

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Questions on Netlink sockets
by Bhaskar Upadhyayula Aug. 25, 2015

Aug. 25, 2015

Hello, I want to check with the group if this is right mailing list to post my question. Here is what I am doing. + From a user-space program, mimicking the behavior of creating a VLAN interface when we execute the following ip command: $ ip link add name <vlan-intf-name> link <parent-intf-name> type vlan id <id> Example: $ ip link add name dummy.110 link dummy type vlan id 110 + My program open's a netlink socket and sends information to kernel (interface names, vlan tags etc). My code more or less follows the code in iproute2/ip/iplink.c + My code is not creating VLAN interface as executed by the 'ip link ...' command. I have a few questions around this and can post my code, if required. But please let me know if this is right mailing list or should I post on netdev list (which I feel is for advanced network questions). Thx.

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Problem with line discipline in new kernels
by Margarita Glushkin Aug. 23, 2015

Aug. 23, 2015

I have a linux kernel driver for serial device, which uses line discipline and char device. Driver works with all old kernels, starting from 3.8 this driver still works, but when I unload it and load again to the memory (modprobe -r bpsctl_mod, after modprobe bpsctl_mod), it crashes the kernel. It can't unregister line discipline, because this line discipline is busy. I use system device, i.e., ttyS0. Here is problematic code: static struct file* bps_file_open(const char* path, int flags, int rights) { struct file* filp = NULL; mm_segment_t oldfs; oldfs = get_fs(); set_fs(get_ds()); filp = filp_open(path, flags, rights); set_fs(oldfs); if (IS_ERR(filp)) return NULL; return filp; } int register_ldisc(void) { int status; // Fill in our line protocol discipline, and register it extbp_drv.ebtty_ldisc.magic = TTY_LDISC_MAGIC; extbp_drv.ebtty_ldisc.name = BP_LDISC_NAME; extbp_drv.ebtty_ldisc.flags = 0; extbp_drv.ebtty_ldisc.open = ebtty_open; extbp_drv.ebtty_ldisc.close = ebtty_close; extbp_drv.ebtty_ldisc.read = NULL; extbp_drv.ebtty_ldisc.write = NULL; extbp_drv.ebtty_ldisc.ioctl = (int (*)(struct tty_struct *, struct file *, unsigned int, unsigned long)) ebtty_ioctl; extbp_drv.ebtty_ldisc.poll = NULL; extbp_drv.ebtty_ldisc.receive_buf = ebtty_receive_buf; extbp_drv.ebtty_ldisc.write_wakeup = NULL; //ebtty_write_wakeup; if ((status = tty_register_ldisc(extbp_drv.line_disc, &extbp_drv.ebtty_ldisc)) == 0) { extbp_drv.drv_state |= ST_LDISC_REGISTRATED; } return status; } int ebtty_init (void) { int status = -1; if (register_ldisc()) { err_print(KERN_ERR, DBG_ERROR, ("Can't register line discipline (%d).\n", line_disc)); goto ebtty_init_exit; } status = 0; ebtty_init_exit: if (status) { dbg_print(KERN_DEBUG, DBG_ERROR, ("Module initialization failed. \n")); cleanup(); } return status; } static void cleanup(void) { int status; if ((status = tty_unregister_ldisc(extbp_drv.line_disc)) != 0) { err_print(KERN_ERR, DBG_ERROR, ("Can't unregister line discipline (err = %d)\n", status)); } } int init_ebtty_module(void) { memset(&port_name_path, 0, sizeof(port_name_path)); printk(BSEM_DRV_NAME BP_VER); sprintf((char *)&port_name_path, "//dev//%s", port_name); fd=bps_file_open((char *)&port_name_path, 0, O_RDWR); memset((void*)&extbp_drv, 0, sizeof(struct ext_bypass_drv)); extbp_drv.drv_name = BP_MOD_NAME; extbp_drv.dev_name = port_name; extbp_drv.line_disc = line_disc; extbp_drv.wait_data = LAST_CHAR; extbp_drv.drv_state = 0; init_waitqueue_head(&extbp_drv.read_wait); if (!ebtty_init()) { extbp_drv.ebtty_major = register_chrdev(0, extbp_drv.drv_name, &ebtty_fops); if (extbp_drv.ebtty_major < 0) { err_print(KERN_ERR, DBG_ERROR, ("can't get major %d\n", extbp_drv.ebtty_major)); return extbp_drv.ebtty_major; } if (fd != NULL) { if (!(bps_vfs_ioctl(fd, TIOCSETD, (unsigned long)&line_disc))) { bps_start_flag = 1; } return 0; } } else { if (fd) filp_close(fd, NULL); cleanup(); return -1; } } void exit_ebtty_module(void) { if (fd) { filp_close(fd, NULL); fd = 0; } cleanup(); } Please advice, maybe I should use something else, instead of line discipline and char device, or maybe I should register and unregister them other way?

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Oops: Kernel access of bad area, sig: 11 [#1]
by Ramon Fried Aug. 23, 2015

Aug. 23, 2015

Hi. I'm developing a driver on PowerPC kernel version 3.10. Once In a while, I get the following OOPS and the system freezes. Unable to handle kernel paging request for data at address 0xffffffdc Faulting instruction address: 0xfb7780c8 Oops: Kernel access of bad area, sig: 11 [#1] When I look at the address where the paging fails, it looks like a wrong address (0xffffffdc). The stack trace points to a list_for_each() macro. Could it be that NULL linked list node container off was called ? Am I in the right direction ? Thanks, Ramon

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detailed process from malloc to memory management
by 慕冬亮 Aug. 22, 2015

Aug. 22, 2015

I want to ask about the detailed process from malloc/alloca library function to memory management. 1. malloc/alloca/realloc and so on 2. heap management in library 3. memory management in linux kernel I only know those simple steps. How do I get the details of each step? The source code of glibc is hard to read. This makes me annoyed. - mudongliang

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How can I set a proxy to let "git send-email" command use it?
by Nan Xiao Aug. 22, 2015

Aug. 22, 2015

Hi all, My Linux server uses a proxy, but I find the "git send-email" command doesn't use the proxy, so the mail can't be sent. How can I set a proxy to let "git send-email" command use it? Thanks very much in advance! Best Regards Nan Xiao

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some question about cpubench
by vichy Aug. 21, 2015

Aug. 21, 2015

hi all: I just finish on cpufreq driver, I have one question, is there any tool that will check timer accuracy for dynamically frequency change? appreciate your help in advance,

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Using gpio from device tree on platform devices.
by Daniel. Aug. 21, 2015

Aug. 21, 2015

Hi all, I'm trying to migrate a driver from board files to device tree. I've added the gpios to device tree. My device is loaded automatically, this is nice, but I'm facing problems while getting gpio from device tree using of_get_property(). Here is the device tree node: powerfailure { compatible = "powerfailure"; poff_pfail = <&gpio5 12 GPIO_ACTIVE_LOW>; irq_pfail = <&gpio5 17 GPIO_ACTIVE_LOW>; }; Here is my driver: http://pastebin.com/4DsRaXMS A simple description of it. There is a circuit that triggers the irq_pfail at failure of power supply. The irq handler then start a clean shutdown. At the end of shutdown pf_power_off to cut the energy from the device. The logic works fine, but I'm having problems on pf_probe function. I got this dump: http://pastebin.com/paTBWwcE So I think I'm doing something wrong with of_get_property returned value. I'm using the kernel 3.14.28 from freescale (iMX6 quad core cpu). What is the right way to get gpio values from device tree? Is that of_get_property() lines right? Thanks in advance, Cheers -- dhs -- "Do or do not. There is no try" Yoda Master

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