August 2011 - kernelnewbies@kernelnewbies.org

ptrace() behaviour when doing PTRACE_KILL
by Pablo Antonio Aug. 29, 2011

Aug. 29, 2011

Hello, I was writing some user code that uses the ptrace() system call and found it wasn't behaving as I expected. Maybe this is simply because I don't know enough about ptrace()'s behaviour, so I'd like someone to enlighten me with some information. So, here's the code: http://codepad.org/TJ7Lua4Q Basically, I was expecting the parent process to kill the child when the later attempted to use the kill() system call, not letting it send signals to other processes. I had done this before with pretty much the same code, but instead of killing when kill() was called, I was doing it when a fork() or clone() was attempted. And it worked. If the child process tried to create a new process via fork() or clone(), then it was immediately killed and no process was created. But now that I'm doing the same thing with kill(), I'm seeing that the child process ends up killed, as expected, but the signal is sent nonetheless. I understand that when I do the PTRACE_KILL, a SIGKILL signal is sent to the child. And PTRACE_KILL is used on syscall entrance in that code. If the SIGKILL signal is delivered to the process before it continues executing the system call in kernelspace, then I don't understand why this code doesn't work as expected. If the signal is delivered after the system call is completely executed, then I don't understand why this was working for the fork() and clone() case. I'd really appreciate if someone told me what's happening here, or what I'm not seeing. Thanks, -- Pablo Antonio (AKA crazy2k) http://www.pablo-a.com.ar/

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Can not free irq 0
by Parmenides Aug. 29, 2011

Aug. 29, 2011

Hi, I wonder how an interrupt handler work, and so try to make one by myself. The first problem is which irq number should I select to hook an interrupt handler on it. In terms of the following messages, I think irq 0 can be adopted because the number of interrupts raised remains 145 and does not increase any more. This case may imply the interrupt handler of rtc clock is not working and can be replaced by another one. Furthermore, I also notice that the Local timer interrupts is increasing, and guess that the clock ticks are driven by this clock chip. That means the irq 0 may be deprecated and its handler can be replaced safely. root [ ~/work/moduleprog ]# cat /proc/interrupts CPU0 0: 145 XT-PIC-XT timer <---- is not working 1: 8 XT-PIC-XT i8042 2: 0 XT-PIC-XT cascade 5: 402 XT-PIC-XT eth0 6: 3 XT-PIC-XT floppy 9: 0 XT-PIC-XT acpi 10: 0 XT-PIC-XT uhci_hcd:usb2 11: 45 XT-PIC-XT ioc0, ehci_hcd:usb1 12: 116 XT-PIC-XT i8042 14: 750 XT-PIC-XT ide0 15: 48 XT-PIC-XT ide1 NMI: 0 Non-maskable interrupts LOC: 4932 Local timer interrupts <---- is working really SPU: 0 Spurious interrupts ... ... ... ... ... The kernel module code: #include <linux/module.h> #include <linux/kernel.h> #include <linux/interrupt.h> static irqreturn_t my_interrupt(int irq, void *dev) { return IRQ_HANDLED; } int init_module(void) { free_irq(0, NULL); if (request_irq(0, my_interrupt, IRQF_SHARED, "myinterrupt", (void *)my_interrupt)){ printk(KERN_ALERT "Can not install interrupt handler of irq 0.\n"); } return 0; } void cleanup_module(void) { } MODULE_LICENSE("GPL"); MODULE_AUTHOR("parmenides"); MODULE_SUPPORTED_DEVICE("mydevice"); Compile it and then invork insmod, I get these messages: Aug 27 23:18:35 lfs kernel: ------------[ cut here ]------------ Aug 27 23:18:35 lfs kernel: kernel BUG at mm/slab.c:521! Aug 27 23:18:35 lfs kernel: invalid opcode: 0000 [#1] SMP Aug 27 23:18:35 lfs kernel: last sysfs file: /sys/kernel/uevent_seqnum Aug 27 23:18:35 lfs kernel: Modules linked in: mydevice(+) Aug 27 23:18:35 lfs kernel: Aug 27 23:18:35 lfs kernel: Pid: 1688, comm: insmod Not tainted 2.6.34 #1 440BX Desktop Reference Platform/VMware Virtual Platform Aug 27 23:18:35 lfs kernel: EIP: 0060:[<c108a835>] EFLAGS: 00010046 CPU: 0 Aug 27 23:18:35 lfs kernel: EIP is at kfree+0x67/0x96 Aug 27 23:18:35 lfs kernel: EAX: 00000000 EBX: c155eb40 ECX: 00000000 EDX: c16cdde0 Aug 27 23:18:35 lfs kernel: ESI: 00000282 EDI: c156fc80 EBP: 00000000 ESP: cf323f70 Aug 27 23:18:35 lfs kernel: DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068 Aug 27 23:18:35 lfs kernel: Process insmod (pid: 1688, ti=cf322000 task=cfbaa030 task.ti=cf322000) Aug 27 23:18:35 lfs kernel: Stack: Aug 27 23:18:35 lfs kernel: c155eb40 00000000 00000000 c1054076 d0846080 00000000 d0846007 d0846010 Aug 27 23:18:35 lfs kernel: <0> c100112d d0846080 00000000 f63d4e2e cf322000 c10517ce 0804b018 080488f0 Aug 27 23:18:35 lfs kernel: <0> c138ba4d 0804b018 00000826 0804b008 080488f0 f63d4e2e bfddbfb8 00000080 Aug 27 23:18:35 lfs kernel: Call Trace: Aug 27 23:18:35 lfs kernel: [<c1054076>] ? free_irq+0x2e/0x40 Aug 27 23:18:35 lfs kernel: [<d0846007>] ? init_module+0x0/0x3d [mydevice] Aug 27 23:18:35 lfs kernel: [<d0846010>] ? init_module+0x9/0x3d [mydevice] Aug 27 23:18:35 lfs kernel: [<c100112d>] ? do_one_initcall+0x44/0x120 Aug 27 23:18:35 lfs kernel: [<c10517ce>] ? sys_init_module+0xa7/0x1d9 Aug 27 23:18:35 lfs kernel: [<c138ba4d>] ? syscall_call+0x7/0xb Aug 27 23:18:35 lfs kernel: Code: e2 05 03 15 c0 65 68 c1 8b 02 25 00 80 00 00 66 85 c0 74 03 8b 52 0c 8b 02 25 00 80 00 00 66 85 c0 74 03 8b 52 0c 80 3a 00 78 04 <0f> 0b eb fe 8b 4a 18 64 a1 e8 5d 5f c1 8b 1c 81 8b 03 3b 43 04 Aug 27 23:18:35 lfs kernel: EIP: [<c108a835>] kfree+0x67/0x96 SS:ESP 0068:cf323f70 Aug 27 23:18:35 lfs kernel: ---[ end trace 00973d9f77f0e389 ]--- The problem is likely caused by free_irq(), but I don't know why and how to resolve it.

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question about oops and panic
by Parmenides Aug. 29, 2011

Aug. 29, 2011

Hi, 1. I think oops and panic are both some way to deal with errors occurs in kernel space. Is there any relationship between them? 2. I make a NULL pointer reference deliberately in a kernel module and get an oops like: ... ... ... Aug 29 00:58:45 lfs kernel: Call Trace: Aug 29 00:58:45 lfs kernel: [<c100112d>] ? do_one_initcall+0x44/0x120 Aug 29 00:58:45 lfs kernel: [<c10517ce>] ? sys_init_module+0xa7/0x1d9 Aug 29 00:58:45 lfs kernel: [<c138d49d>] ? syscall_call+0x7/0xb ... ... ... I wonder what is the meaning of the tow numbers after a function name.

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BlueTooth: HCI: Error message
by Pradeep Kumar Aug. 29, 2011

Aug. 29, 2011

Hi, I am seeing following error in dmesg log while I am trying to receive data(to my HTC mobile phone running Android Froyo) over BT from some external device. >> hci_acldata_packet: hci0 ACL packet for unknown connection handle can some one help me in decoding it? when would we see such message.? thanks Pradeep

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understanding GPIO registers
by OrazioPirataDelloSpazio (Lorenzo) Aug. 28, 2011

Aug. 28, 2011

Hi there, I have a motherbord (VIA EPIA LT) with a digital I/O port composed by 4 GPI and 4 GPO (chip: SMSC SCH3114). I want to provide voltage to GPO and read the input value of GPI with a software. Using the generic gpio kernel module, I tried to export pins without success : echo N > /sys/class/gpio/export write error : invalid argument I tried for several values of N (from 1 to 1000 !) then I gave up thinking I would have needed some information from the hardware producer. Now I have got this information that is the following offsets and addresses. How can I use these registers to fix the export problem or alternatively how to write a simple userspace C program to read and write these GPIO? I read gpio.txt but I'm still confused on how to pass from GPIO numbers to registers. Thanks Lorenzo #define sGPIOBaseAddr 0A00 #define GPI1_CTRL_REG 0x6E #define GPI2_CTRL_REG 0x6F #define GPI3_CTRL_REG 0x72 #define GPI4_CTRL_REG 0x73 #define GPO1_CTRL_REG 0x2C #define GPO2_CTRL_REG 0x2D #define GPO3_CTRL_REG 0x35 #define GPO4_CTRL_REG 0x36

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I need suggestions for a practical work related with Kernel Development
by Facundo Viale Aug. 27, 2011

Aug. 27, 2011

Hi! I'm new here and i what to introduce myself i'm teacher in a University in the course Operation Systems. During the course the students learn some Operatyng Systems concepts, specially everything relating to the Kernel. As a practice task, they also have to use C to make a program with some Kernel functionalities. This year this task consists on programming a File System (I chose FAT32 since I thought it was the easiest one to implement) using FUSE and simulating a Hard Disk and a RAID behavior. Since I'm not a Kernel expert I'm looking for some advice and ideas. The aim of the practice task I'm creating is to help the students make a program that simulates the behavior and functionalities of a Kernel (such as a File System, Memory Administrator, Planner, etc.), but at the same I would like those programs to really interact with the Kernel, being not only ideal simulation cases (like FUSE). But, as I said, I don't know that much to have a good idea of what can I use to make the most from the Kernel in the task. I could really use some ideas! Some of the things I have in mind: - Use netlinks - Build a kernel module - I'm also interested in the /dev/mem ¡Thanks a lot in advance!

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Need help with the Uncompressed kernel be overriden after decompress_kernel called?
by jiangtao.jit Aug. 27, 2011

Aug. 27, 2011

Hi all. In arch/x86/boot/compressed/head_32.S before the call of decompress_kernel() it load the address of z_extract_offset_negative(%ebx) as the output address and actually the output_len of the decompressed kernel is larger than extract_offset so the decompressed data will override the uncompressed data begin at input_data Is that the case? How does it worked as the the input buffer is covered by the output buffer while uncompressing? It confused me a lot. or I'd made some misunderstanding on the decompressing routine? Thanks. 2011-08-27 jiangtao.jit

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The core in which NAPI is using
by J.Hwan Kim Aug. 27, 2011

Aug. 27, 2011

Hi, everyone My ethernet card always interrupts at Core 0 . The driver of the device is using NAPI. When NAPI is appled, does the core in which NAPI is processing vary? Is the NAPI triggered by software interrupt, isn't it? My system monitor indicates the CPU loading varies randomly among 8 cores. Can you give an information if the core which NAPI is using varies? Thanks in advance. Best Regards, J.Hwan Kim

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(struct spi_transfer)->rx_buf == (struct spi_transfer)->tx_buf?
by Arvid Brodin Aug. 26, 2011

Aug. 26, 2011

I was tracing calls to dma_map_single() and noticed that spi drivers call this function repeatedly on the same buffer address (with no dma_unmap_single() between). Is this really OK? Looking into it I saw that the spi drivers' tx_buf and rx_buf were equal (same address), and these are "dma mapped" simultaneously in many spi drivers (tx_buf as DMA_TO_DEVICE; rx_buf as DMA_FROM_DEVICE). If this buffer (tx_buf === rx_buf) is both read from and written to using DMA, then shouldn't they use DMA_BIDIRECTIONAL? Also, DMA_TO_DEVICE mappings should be done before starting the transfer to the device, while DMA_FROM_DEVICE mappings should be done after the device has finished its transfer, if I understand dma_map_single() correctly (because this is just a cache synchronization thing, right?) This whole thing just seemed strange to me and I'm hoping someone can explain what's going on! BTW, the declaration of struct spi_transfer (http://lxr.linux.no/linux+*/include/linux/spi/spi.h#L430) has this comment: /* it's ok if tx_buf == rx_buf (right?) */ Since spi is always full duplex, I'm guessing that the idea with using only one buffer is that incoming bytes overwrites queued bytes? -- Arvid Brodin Enea Services Stockholm AB

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How to understand 'make oldconfig'?
by Parmenides Aug. 26, 2011

Aug. 26, 2011

Hi, I have tried to understand 'make oldconfig' command while configurating kernel. I do some experiments and get the following ideas: 1. When there is no a .config in /usr/src/linux, (1) If there is no a /boot/config-x.y.z, make will ask some questions and then produce a .config. (2) Otherwise, make will copy the /boot/config-x.y.z to /usr/src/linux/.config. My question: According to the messages generated by make, I get that both 'make defconfig' and 'make oldconfig' will gerenate .config based on 'i386_defconfig'. Why does 'make oldconfig' ask some questions, while 'make defconfig' does not? 2. When there is a .config in /usr/src/linux indeed, make do nothing but generate a copy of .config, namely .config.old. My question: According to Love, "After making changes to your configuration file, or when using an existing configuration file on a new kernel tree, you can validate and update the configuration: make oldconfig." But, whether I edit .config and make some changes or I copy an existing .config into /usr/src/linux, 'make oldconfig' seems do nothing. So, how can I understand 'make oldconfig' in this case?

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