October 2014 - kernelnewbies@kernelnewbies.org

BUG: unable to handle kernel NULL pointer dereference at (null)
by Kevin Wilson Oct. 23, 2014

Oct. 23, 2014

Hello, I am getting this message when running a patched kernel: BUG: unable to handle kernel NULL pointer dereference at (null) Is there some kernel configuration item which enables getting , instead "(null)", the proper value (I assume it should be a method name) Regards, Kevin

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i2c-dev
by John de la Garza Oct. 22, 2014

Oct. 22, 2014

I have my kernel built with dev-i2c and i2c_i801 but do not have a /dev entry. lspci shows this: 00:1f.3 SMBus: Intel Corporation 5 Series/3400 Series Chipset SMBus Controller (rev 06) dmesg shows this: [ 1.566003] i801_smbus 0000:00:1f.3: enabling device (0000 -> 0003) ls /sys/bus/i2c/devices/ shows nothing... on running this on a MacBookPro6,2 What am I missing? Shouldn't I see a i2c device? I think SMBus is a subset of i2c and I should be able to use that subset, right?

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[PATCH] staging: Fix checkpatch issue with brackets in rtw_ap.c
by Nicholas Krause Oct. 22, 2014

Oct. 22, 2014

Fix checkpatch error message with opening bracket of if statement, not being on the same line as a if statement in rtw_ap.c Signed-off-by: Nicholas Krause <xerofoify(a)gmail.com> --- drivers/staging/rtl8723au/core/rtw_ap.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/drivers/staging/rtl8723au/core/rtw_ap.c b/drivers/staging/rtl8723au/core/rtw_ap.c index 6b4092f..927b2a6 100644 --- a/drivers/staging/rtl8723au/core/rtw_ap.c +++ b/drivers/staging/rtl8723au/core/rtw_ap.c @@ -1567,8 +1567,7 @@ void bss_cap_update_on_sta_join23a(struct rtw_adapter *padapter, struct sta_info } } - if (rtw_ht_operation_update(padapter) > 0) - { + if (rtw_ht_operation_update(padapter) > 0) { update_beacon23a(padapter, WLAN_EID_HT_CAPABILITY, NULL, false); update_beacon23a(padapter, WLAN_EID_HT_OPERATION, NULL, true); } -- 1.9.1

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understanding cpuidle
by Ran Shalit Oct. 21, 2014

Oct. 21, 2014

Hello, I try to understand the cpuidle main concept but have some difficulties. I could not find any documentation to explain the cpuidle. what does it mean that it enters idle when "no thread to run" ?if I have only one process which does only while(1) { printf("C"); mdelay(1000); } Can I expect it to enter idle for 1 second and then print "C" and get again to idle ? Thanks Ran

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booting kernel with kvm
by harisha ja Oct. 18, 2014

Oct. 18, 2014

Hi All, I am interested in Linux kernel development. I have subscribed for newbies mail for a while and this is my first mail to the group. My intention and interest is to work on network( if possible mm) side of kernel. First of all thanks for all the kernel developers and the guys here for contribution to Linux community. Here is my doubt. 1) I downloaded the linux source code and created the config using make defconfig and created image using make ( I did not do make install as I want test it with kvm) I have windows 7 system and I have installed ubuntu using vmware. I have installed KVM on ubuntu and I am trying to boot the kernal image with KVM. But I am not sure what is the problem. I am stuck in this screen. Is something I am missing here? The approach using kvm to put some logs and to see module initialization is wrong?. The command I am using kvm -kernel ./arch/x86/boot/bzImage -append root=/root/ I see the below message and then the qemu prompt does not boot and stops by displaying below traceback. Could not access KVM kernel module: No such file or directory failed to initialize KVM: No such file or directory QEMU 5.1654731 Stack: 5.1654731 c18ea844 claea9a0 00000000 fffffffa d?861efc 00008001 d?8611 a35f91 5.1654731 cl8ddba8 d?861efc d7861efc fffffffa 00000000 d7b6e000 cl8dd6 ff3dc0 5.1654731 d7b6e000 6e6b6e75 2d6e??61 636f 6c62 2c30286b c1002930 d78611 13c248 5.1654731 Call Trace: 5.1654731 l<c1a35f91>1 mount_block_root+Ox158/0x1de 5.1654731 l<c1002930>1 ? do_general_protection+0x40/0x170 5.1654731 l<c113c248>1 ? SyS_mknod+0x28/0x30 5.1654731 l<cla3610a>1 mount_root+Oxf3/Oxfb 5.1654731 l<c1a36235>1 prepare_namespace+0x123/0x167 5.1654731 l<c112cf30>l ? SyS_access+0x20/0x30 5.1654731 l<cla35cf7>1 kernel_init_freeable+Ox1b5/0x1c2 5.1654731 l<c1a35545>1 ? do_early_param+0x74/0x74 5.1654731 l<c174caab>1 kernel_init+Oxb/Oxe0 5.1654731 l<c175a041>1 ret_from_kernel_thread+0x21/0x30 5.1654731 l<c174caa0>1 ? rest_init+0x60/0x60 5.1654731 Code: 00 00 00 00 31 ff 83 3d 8c a9 ae cl 00 74 05 e8 Oe dO 9 c? 44 24 04 a0 a9 ae cl c7 04 24 44 a8 Be cl e8 b6 05 00 00 fb 3116 <35>1 15 83 75 f0 01 8b 45 f0 ff 15 80 a9 ae cl 01 c6 8d be 5.1654731 EIP: l<c174f2e9>1 panic+0x165/0x197 SS:ESP 0068:d7861eb8 5.1654731 --I end trace a4Obaf277b417d8d 1-- Thanks Harish

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epoll improvements
by Nev Ikte Oct. 17, 2014

Oct. 17, 2014

Hi, I've a server using epoll and I've noticed that when the traffic is low, the epoll_wait() latency goes up. I've tried to reproduce it with a single client and basically, if ep_poll() is able to find an event or the timeout is 0, the latency is down to 5usec, otherwise if it enters the waitqueue the latency goes up to 10-25usec, which impact the application performance. Looking at the code there is something like a todo ("Is it worth to try to dig for events ?") https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/fs/eve… Anyone knows how the situation can be improved? in theory having something like a 50usec spin loop checking for events before entering in the waitqueue should improve the situation. suggestion? patches? thanks!

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USB Start Learning Codebase
by nick Oct. 17, 2014

Oct. 17, 2014

Hey Guys, I am asking here about how to start with the usb stack as I am interested in learning that alongside the btrfs codebase. Nick

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Share the project directory or a patch?
by Freeman Zhang Oct. 16, 2014

Oct. 16, 2014

Hi list, I'm building a kernel module (a stackable file system) with some userspace tools, and I'd like to share them. I don't know if I should share it in the form of patch or just as a pack of source codes. Under which circumstances do I need to make a patch? All the best! Freeman

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Socket receive, send
by Grzegorz Dwornicki Oct. 14, 2014

Oct. 14, 2014

Hey Is there a good documentation on how messages are taking the tour from User calling read/write on socket fd, to kernel handling the actual send/receive functions? I wish to write code to capture the messages (no netfilter - I wish to bypass it) for processing. I know there is a socket->ops structure with functions pointers. I am at the point to look the inet version on that pointers. But if there is a documentation on this it will save me some time. Grzegorz.

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How to debug this condition of "eth2: tx hang 1 detected on queue 11, resetting adapter" ?
by lx Oct. 14, 2014

Oct. 14, 2014

hi all: I want to send sk_buff by "dev_queue_xmit", when I just send 2 packets, the network card may be hang. I want to know how to debug this condition. the /var/log/messages is: ######################################### [root@10g-host2 test]# tail -f /var/log/messages Sep 29 10:38:22 10g-host2 acpid: waiting for events: event logging is off Sep 29 10:38:23 10g-host2 acpid: client connected from 2018[68:68] Sep 29 10:38:23 10g-host2 acpid: 1 client rule loaded Sep 29 10:38:24 10g-host2 automount[2210]: lookup_read_master: lookup(nisplus): couldn't locate nis+ table auto.master Sep 29 10:38:24 10g-host2 mcelog: failed to prefill DIMM database from DMI data Sep 29 10:38:24 10g-host2 xinetd[2246]: xinetd Version 2.3.14 started with libwrap loadavg labeled-networking options compiled in. Sep 29 10:38:24 10g-host2 xinetd[2246]: Started working: 0 available services Sep 29 10:38:25 10g-host2 abrtd: Init complete, entering main loop Sep 29 10:39:41 10g-host2 kernel: vmalloc mmap_buf=ffffc90016e29000 mmap_size=4096 Sep 29 10:39:41 10g-host2 kernel: insmod module wsmmap successfully! Sep 29 10:39:49 10g-host2 kernel: mmap_buf + 1024 is ffffc90016e29400 Sep 29 10:39:49 10g-host2 kernel: data ffffc90016e2942a, len is 42 Sep 29 10:39:49 10g-host2 kernel: udp data ffffc90016e29422 Sep 29 10:39:49 10g-host2 kernel: ip data ffffc90016e2940e Sep 29 10:39:49 10g-host2 kernel: eth data ffffc90016e29400 Sep 29 10:39:49 10g-host2 kernel: h_source is ffffc90016e29406, dev_addr is ffff880c235c4750, len is 6result is 0 Sep 29 10:39:50 10g-host2 kernel: mmap_buf + 1024 is ffffc90016e29400 Sep 29 10:39:50 10g-host2 kernel: data ffffc90016e2942a, len is 42 Sep 29 10:39:50 10g-host2 kernel: udp data ffffc90016e29422 Sep 29 10:39:50 10g-host2 kernel: ip data ffffc90016e2940e Sep 29 10:39:50 10g-host2 kernel: eth data ffffc90016e29400 Sep 29 10:39:50 10g-host2 kernel: h_source is ffffc90016e29406, dev_addr is ffff880c235c4750, len is 6result is 0 Sep 29 10:39:52 10g-host2 kernel: ixgbe 0000:03:00.0: eth2: Detected Tx Unit Hang Sep 29 10:39:52 10g-host2 kernel: Tx Queue <11> Sep 29 10:39:52 10g-host2 kernel: TDH, TDT <0>, <5> Sep 29 10:39:52 10g-host2 kernel: next_to_use <5> Sep 29 10:39:52 10g-host2 kernel: next_to_clean <0> Sep 29 10:39:52 10g-host2 kernel: ixgbe 0000:03:00.0: eth2: tx_buffer_info[next_to_clean] Sep 29 10:39:52 10g-host2 kernel: time_stamp <fffd3dd8> Sep 29 10:39:52 10g-host2 kernel: jiffies <fffd497f> Sep 29 10:39:52 10g-host2 kernel: ixgbe 0000:03:00.0: eth2: tx hang 1 detected on queue 11, resetting adapter Sep 29 10:39:52 10g-host2 kernel: ixgbe 0000:03:00.0: eth2: Reset adapter Sep 29 10:39:52 10g-host2 kernel: ixgbe 0000:03:00.0: master disable timed out Sep 29 10:39:53 10g-host2 kernel: ixgbe 0000:03:00.0: eth2: detected SFP+: 5 Sep 29 10:39:54 10g-host2 kernel: ixgbe 0000:03:00.0: eth2: NIC Link is Up 10 Gbps, Flow Control: RX/TX ######################################### some information of my computer is: ######################################### ethtool -i eth2 driver: ixgbe version: 3.21.2 firmware-version: 0x1bab0001 bus-info: 0000:03:00.0 supports-statistics: yes supports-test: yes supports-eeprom-access: yes supports-register-dump: yes supports-priv-flags: no LSB Version: :base-4.0-amd64:base-4.0-noarch:core-4.0-amd64:core-4.0-noarch:graphics-4.0-amd64:graphics-4.0-noarch:printing-4.0-amd64:printing-4.0-noarch Distributor ID: CentOS Description: CentOS release 6.5 (Final) Release: 6.5 Codename: Final ######################################### kernel version is: 2.6.32-431.el6.x86_64 Thank you for your help.

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