March 2014 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

Need of KDB patch for powerpc Architecture
by Jegathesan Durairaj March 18, 2014

March 18, 2014

Hi, I am using Linux Kernel Version 2.6.34.6 with powerPC. I knew that KDB was merged with Kernel mainline 2.6.35. Hence I need to apply KDB patch with my kernel, But I couldn't find any patch for powerPC in the following place ftp://oss.sgi.com/www/projects/kdb/download/ Can you help me to get patch for powerpc? Thanks Jegan

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"Recursive entry to debugger" panic seen with KGDB (PowerPC)
by Jegathesan Durairaj March 17, 2014

March 17, 2014

I am using Linux Kernel Version 2.6.34.6 SMP for powerPC 64 bit. I tried to debug kernel using KGDB and ended up in Kernel panic reboot issue. Here is the list of steps I did. 1) I enabled the following in the config file CONFIG_DEBUG_PAGEALLOC=y CONFIG_DEBUG_KERNEL=y CONFIG_DEBUG_INFO=y CONFIG_KGDB=y CONFIG_FRAME_POINTER=y CONFIG_KGDB_SERIAL_CONSOLE=y Built and loaded the Kernel. 2) My Linux PC is connected terminal server using ttyS0 and I enabled KGDB over serial port by doing "echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc" 3) Trigger KGDB by issuing sysrq-g. echo g > /proc/sysrq-trigger 4) Kernel Panic reboot is seen with the following reboot log sw0:root> echo ttyS0 > /sys/module/kgdboc/parameters/kgdboc kgdb: Registered I/O driver kgdboc. sw0:root> echo g > /proc/sysrq-trigger SysRq : DEBUG Entering KGDB Unable to handle kernel paging request for instruction fetch Faulting instruction address: 0x00000000 KGDB: re-enter exception: ALL breakpoints killed Call Trace: STACK MAGIC 0x57ac6e9d [813679c0] [40007fcc] show_stack+0x84/0x24c (unreliable) [81367a20] [4057d9f4] dump_stack+0x2c/0x44 [81367a30] [40098008] kgdb_handle_exception+0x184/0x1b8 [81367a80] [40013320] kgdb_debugger+0x88/0xa0 [81367a90] [4000f5a4] die+0x48/0x28c [81367ac0] [40019460] bad_page_fault+0x90/0xe0 [81367ae0] [400123fc] handle_page_fault+0x7c/0x80 [81367ba0] [407a0000] kmalloc_caches+0xdc0/0x1340 [81367bb0] [402d11ac] uart_poll_get_char+0x58/0x70 [81367bc0] [402daae8] kgdboc_get_char+0x40/0x58 [81367bd0] [40096eac] kgdb_cpu_enter+0x420/0x1320 [81367c60] [40097f08] kgdb_handle_exception+0x84/0x1b8 [81367cb0] [40013250] kgdb_handle_breakpoint+0x4c/0x94 [81367cc0] [40578dbc] program_check_exception+0x5c/0x860 [81367da0] [40012544] ret_from_except_full+0x0/0x4c [81367e60] [40096018] sysrq_handle_gdb+0x94/0xb0 [81367e70] [402c9f28] __handle_sysrq+0xe0/0x1c8 [81367ea0] [402ca06c] write_sysrq_trigger+0x5c/0x80 [81367eb0] [401614a4] proc_reg_write+0x90/0xcc [81367ee0] [4011201c] vfs_write+0xb4/0x1a8 [81367f00] [401122b0] sys_write+0x60/0x144 [81367f40] [40011f4c] ret_from_syscall+0x0/0x3c Kernel panic - not syncing: Recursive entry to debugger Call Trace: STACK MAGIC 0x57ac6e9d Can you help me to understand the root cause of the issue? Let me know how to solve this issue. Thanks Jegan

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/proc/slab_allocatos
by Pietro Paolini March 17, 2014

March 17, 2014

Hello everyone, what is the meaning of the number 578 (in this case) in the output of /proc/slab_allocatos root@drgos:~# cat /proc/slab_allocators | grep skb skbuff_head_cache: 578 __alloc_skb+0x38/0x114 root@drgos:~# Are those bytes, Kbytes, or am I completely wrong ? Best Regards, Pietro.

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extract patch's from the mail.
by Anand Moon March 17, 2014

March 17, 2014

Hi All, Please share the method to extract patch form the mail. Generally patch have comment and diff of the files changes, so which part we need to select for the patch file. Please share your thoughts. -Anand Moon

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threads context switch
by Nada Saif March 17, 2014

March 17, 2014

Hi all, I need to write a C code to measure time spent in threads context switch-- any tips how to do that? Thanks, Nada

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RE: Please help.. trying to use USB keyboard to open a shell on LCD display
by Chan Kim March 17, 2014

March 17, 2014

There is no reponse yet to this question.. any help/hint would be appreciated. I found that I may have to use getty in the /etc/inittab file to get tty for a vc. For busybox, the example in init/init.c suggests entries like tty4::respawn:/sbin/getty 38400 tty4 I earlier found the keyboard seems to be connected to tty1 and the printk output is switched to tty1 towards the end during the initialization. So I tried in the inittab tty1::respawn:/sbin/getty 38400 tty1 and 1::respawn:/sbin/getty 38400 tty1 But didn't work. I know how to start a shell on tty1 (using inittab). But How do I map tty1 to the vc and to the LCD using boot argument or busybox setting? This seems to be the key question. Thansk, Chan ________________________________ From : "Kim Chan" <ckim(a)etri.re.kr> Sent : 2014-03-12 15:31:17 ( +09:00 ) To : kernelnewbies(a)kernelnewbies.org <kernelnewbies(a)kernelnewbies.org> Cc : Subject : Please help.. trying to use USB keyboard to open a shell on LCD display Hello, folks, It is a comfort to me that I have people to ask questions here and I hope I could be answering to some hard quetions someday. I've beeing trying to attach a USB keyboard to our embedded system to open a shell on the LCD display using framebuffer console. The USB host controller is from the opencore(USB1.1) and it works for USB memory. Some of the boot arguments are (I've tried some variants) "console=tty1 " "fbcon=map:0000,font:SUN8x16,vc:1-3 " "root=/dev/ram " The problem is, after the final sys_execve() which executes /sbin/init of the ramdisk, I cannot see any printf results frome the busybox init_main function not to mention the shell. So I cannot use shell commands like getty. Using uart as the console I can see printf results in the busybox init_main routine. (I use "console=ttyS,mmio,0xff003000,115200n8 " in that case) Using some prints on separate uart print routine, I can see from the kbd_event function that the key value is going to current vc which is using tty1. The key value is then handed to put_queue function where the character is somehow copied to tty buffer. Flush_to_ldisc is scheduled for it and it will probably get passed on to the virtual console. By the way, I guess the keyboard data is delivered to current fg_console (vc 0 which is using tty1). Added to this, there is a notifier_call_chain and the notifier block is registered by vcs_poll_data_get function which I don't know weather is necessary or not. So one of my questions is if vcs is necessary for my case. (I guess not. There is no other notifier blocks registered) I gathered that without inittab (I don't use inittab which should be ok for most cases) the assumed default inittab tty2::askfirst:-/bin/sh tty3::askfirst:-/bin/sh tty4::askfirst:-/bin/sh is being applied by the busybox so there maybe 3 shells on tty2,tty3, and tty4 running somewhere. But even if there are shells running I don't know how to switch to those ttys. I tried using Ctrl-Alt F2 (or F3, F4) using the USB keyboard to switch to tty2,3,4 to see if any shell comes up on the LCD but couldn't see it. I tried using inittab with no avail before. And I don't know how the printf in busybox is connected to the kernel. I guess busybox talks with stdio(stdout,stdin..) and the file is connected to the kernel anyhow. I've digged up how vc driver is connected to the console switch functions and to the bit blitting functions and how the printk is handled in the kernel. But these console, tty, framebuffer console.. things are very complex to me. and I hope somebody could point me to what should be checked. Any hint will be deeply appreciated. Best Regards, Chan _______________________________________________ Kernelnewbies mailing list Kernelnewbies(a)kernelnewbies.org<mailto:Kernelnewbies@kernelnewbies.org> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

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how to determine kernel interrupt latency
by loody March 16, 2014

March 16, 2014

hi all: is it possible to determine interrupt latency in kernel with any ftrace or proc? -- Regards,

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Problem while compiling my module on downloaded kernel source
by Rahul Garg March 15, 2014

March 15, 2014

Hi, Being newbie to kernel, I downloaded the source code of stable kernel code[3.13.6]. Then I build it using make oldconfig && make prepare. Now when I am trying build my kernel module against this source code. But I am unable to do so, Here is the error I am getting make -C /home/rahul/linux-3.13.6 M=/home/rahul/KerenelTryouts modules make[1]: Entering directory `/home/rahul/linux-3.13.6' WARNING: Symbol version dump /home/rahul/linux-3.13.6/Module.symvers is missing; modules will have no dependencies and modversions. CC [M] /home/rahul/KerenelTryouts/test.o /bin/sh: 1: /home/rahul/linux-3.13.6/scripts/recordmcount: not found make[2]: *** [/home/rahul/KerenelTryouts/test.o] Error 127 make[1]: *** [_module_/home/rahul/KerenelTryouts] Error 2 make[1]: Leaving directory `/home/rahul/linux-3.13.6' make: *** [all] Error 2 Here is my make file for your reference KERNELDIR=/home/rahul/linux-3.13.6 obj-m += test.o all: ifneq ($(KERNELDIR), ) make -C $(KERNELDIR) M=$(PWD) modules else make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules endif clean: make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean Please help me out with this. Regards Rahul

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how to "rmmod module"
by 于运超 March 15, 2014

March 15, 2014

Hi, when u insmod module,yours PC maybe dump. and u can not rmmod your module except reboot. i want to know has other ways to solution module loader error?

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Is my custom field added in page struct guaranteed zero when a page is allocated ?
by 朱 March 14, 2014

March 14, 2014

hi, I add a u64 field in struct page to record corresponding disk sector postion. I will change and read this field when dealing with page cache staff. I want it stays zero unless my code change its value. Will the kernel 's allocating code guarantee that the field is zero when the page is allocated? or Need I add some code to the allocating routine to explicitly fill the field with zero? Regard， Lingyu Zhu

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