September 2015 - kernelnewbies@kernelnewbies.org

Help debugging linux-next.
by Lucas Tanure Sept. 13, 2015

Sept. 13, 2015

Hi, I would like some tips about how debug a issue with linux-next. I'm trying to find things to do in kernel, and the first thing is boot the linux-next tree. I'm able to compile the source, but when I boot I got a black screen a few times, or a just a warn in dmesg. I'm trying to understand the issue, but no success. I tried to get kdump from the issue, but didn't work. I also tried to go back a few commits in linux-next, but my system doesn't boot at all. How I can find the commit that create the problem, since every commit that I tested I got black screen ? Whats the best way to debug this kind of issue ? Thanks! My full warning: ------------[ cut here ]------------ WARNING: CPU: 3 PID: 243 at drivers/gpu/drm/drm_drv.c:569 drm_dev_alloc+0x251/0x320 [drm]() Modules linked in: i915(+) joydev input_leds mousedev intel_rapl iosf_mbi x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm ttm hid_generic drm_kms_helper crct10dif_pclmul snd_hda_intel crc32_pclmul usbhid snd_hda_codec crc32c_intel drm hid ghash_clmulni_intel snd_hda_core eeepc_wmi asus_wmi aesni_intel iTCO_wdt sparse_keymap snd_hwdep led_class aes_x86_64 lrw snd_pcm iTCO_vendor_support rfkill mxm_wmi evdev gf128mul intel_gtt e1000e glue_helper mac_hid snd_timer syscopyarea ablk_helper cryptd sysfillrect psmouse snd sysimgblt pcspkr fb_sys_fops ptp mei_me i2c_i801 i2c_algo_bit soundcore mei shpchp i2c_core pps_core lpc_ich serio_raw wmi fan battery processor thermal video button sch_fq_codel ip_tables x_tables ext4 crc16 mbcache jbd2 sd_mod atkbd libps2 ahci libahci libata xhci_pci xhci_hcd ehci_pci ehci_hcd scsi_mod usbcore usb_common i8042 serio CPU: 3 PID: 243 Comm: systemd-udevd Not tainted 4.2.0-next-20150912-ARCH #5 Hardware name: System manufacturer System Product Name/Maximus IV GENE-Z, BIOS 3603 11/09/2012 0000000000000000 000000005ca47666 ffff88060f70b9d0 ffffffff812b9159 0000000000000000 ffff88060f70ba08 ffffffff81074e62 ffff880612d39000 ffffffffa06c7100 ffff880612f66098 ffffffffa06c7100 ffffffffa0691760 Call Trace: [<ffffffff812b9159>] dump_stack+0x4b/0x72 [<ffffffff81074e62>] warn_slowpath_common+0x82/0xc0 [<ffffffff81074faa>] warn_slowpath_null+0x1a/0x20 [<ffffffffa0422291>] drm_dev_alloc+0x251/0x320 [drm] [<ffffffffa0424d0b>] drm_get_pci_dev+0x3b/0x1e0 [drm] [<ffffffffa05dd2d4>] i915_pci_probe+0x34/0x50 [i915] [<ffffffff812fdec5>] local_pci_probe+0x45/0xa0 [<ffffffff812fde10>] ? pci_match_device+0xe0/0x110 [<ffffffff812ff053>] pci_device_probe+0x103/0x150 [<ffffffff813d7942>] driver_probe_device+0x222/0x490 [<ffffffff813d7c34>] __driver_attach+0x84/0x90 [<ffffffff813d7bb0>] ? driver_probe_device+0x490/0x490 [<ffffffff813d557c>] bus_for_each_dev+0x6c/0xc0 [<ffffffff813d70fe>] driver_attach+0x1e/0x20 [<ffffffff813d6c4b>] bus_add_driver+0x1eb/0x280 [<ffffffff813d8540>] driver_register+0x60/0xe0 [<ffffffff812fd73c>] __pci_register_driver+0x4c/0x50 [<ffffffffa0424f90>] drm_pci_init+0xe0/0x110 [drm] [<ffffffffa06e6000>] ? 0xffffffffa06e6000 [<ffffffffa06e60a4>] i915_init+0xa4/0xab [i915] [<ffffffff81002123>] do_one_initcall+0xb3/0x200 [<ffffffff81199801>] ? __vunmap+0x91/0xe0 [<ffffffff811589a0>] do_init_module+0x5f/0x1ef [<ffffffff810fa707>] load_module+0x2197/0x27e0 [<ffffffff810f7550>] ? symbol_put_addr+0x50/0x50 [<ffffffff81188695>] ? __pte_alloc_kernel+0xa5/0xf0 [<ffffffff810fae9e>] SyS_init_module+0x14e/0x190 [<ffffffff8157046e>] entry_SYSCALL_64_fastpath+0x12/0x71 ---[ end trace d2652104b24a32ff ]---

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What's the difference between /proc/vmcore and /proc/kcore ?
by Lucas Tanure Sept. 13, 2015

Sept. 13, 2015

Hi, What's the difference between /proc/vmcore and /proc/kcore ? Thanks -- Lucas Tanure

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Tips for Kernel Module Debugging
by Lucas Tanure Sept. 12, 2015

Sept. 12, 2015

Hi, I'm testing the linux-next tree and I got this stack: [ 2.158054] Call Trace: [ 2.158058] [<ffffffff812b9159>] dump_stack+0x4b/0x72 [ 2.158061] [<ffffffff81074e62>] warn_slowpath_common+0x82/0xc0 [ 2.158063] [<ffffffff81074faa>] warn_slowpath_null+0x1a/0x20 [ 2.158066] [<ffffffffa0572291>] drm_dev_alloc+0x251/0x320 [drm] [ 2.158070] [<ffffffffa0574d0b>] drm_get_pci_dev+0x3b/0x1e0 [drm] [ 2.158081] [<ffffffffa07062d4>] i915_pci_probe+0x34/0x50 [i915] How is the best way to debug this ? I really need to add a print, compile and boot many times ? How would you guys debug this ? I know a way to boot two kernels, and the second get the dump from the first. But this isn't a Oops or Panic, it's just a warning. So the second kernel will not be triggered. Tips ? Thanks -- Lucas Tanure +55 (19) 988176559

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Set the ACPI=on on the cmdline, and the OS can not boot.
by tianlilai Sept. 10, 2015

Sept. 10, 2015

Hi,Everyone,I have a problem as follow: When I set the ACPI=on on the cmdline,and the OS can not boot(If set ACPI=off, The system is OK). The attachmemt file is the booting log. Would help me slove this ploblem? Thanks very much. Note:kernel version v2.6.18,and the arch is x86_64. Regards laitianli

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Use a variable before it's declaration
by Rock Lee Sept. 10, 2015

Sept. 10, 2015

Hi, all: Here is a snippet of linux-v3.4 which drives me crazy. Because init_task hasn't been declared yet when init_thread_union is initializing. Why is there no compiling error? Any hint would be helpful. union thread_union init_thread_union __init_task_data = { INIT_THREAD_INFO(init_task) }; /* * Initial task structure. * * All other task structs will be allocated on slabs in fork.c */ struct task_struct init_task = INIT_TASK(init_task); -- Rock Lee

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SPI operations on interrupt context!?
by Daniel. Sept. 9, 2015

Sept. 9, 2015

Hi all, I'm dealing with a SPI driver and I have a doubt. I need to read and write data to spi (registers and values) inside interrupt handler. I want to know if this pattern is safe or if I'll face problems with it. This code is being added to gpio-mcp23s08.c driver to handle IRQ and save INTCAP at interruption time. INTCAP register keeps the input port status at interruption time. I want to capture this as fast as possible and put it at a circular queue. I write this code inspired by spi_sync function, but using spinlocks so it doesn't sleeps. But, these spin_(un)lock calls seems a bad ideia to me. Any better idea or guidelines? Here is the code. https://gist.github.com/gkos/4cce494e90518077084a#file-gpio-mcp23s08-c-L440 The functions are mcp23s17_read_irqsafe and mcp23s17_read_irqsafe_complete PS: The code is a little messed up (because I've been trying to optimize this INTCAP capturing by many means) Cheers - dhs -- *"Do or do not. There is no try"* *Yoda Master*

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Videobuf2's vb2_dqbuf return (-EINVAL) error on streamoff
by Chetan Nanda Sept. 9, 2015

Sept. 9, 2015

Hi, I am working on a V4L2 based video decoder driver, At user side there are two contexts. One is queuing/dequeuing buffers from driver (in a separate thread) and other is the main context, from where I am calling streamon, streamoff. When I call a streamoff from main context and thread is blocking on dqbuf, This cause the blocking thread to unblock from dqbuf with an error (EINVAL). Seems this error coming from videobuf2-core, as streamoff will unblock the waiting thread, and this thread will go and check (in function __vb2_wait_for_done_vb) for q->streaming and will return error as q->streaming will be set to false on streamoff. Is it the right behavior of vb2_dqbuf to return error when streamoff is called? Or is it a right way to have this kind of mechanism i.e.on userside one thread is queue/dequeue buffers while another is doing streamoff. Thanks for your help and idea. Thanks, Chetan Nanda

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Eudyptula task 2
by Yacdaniel Hurtado García Sept. 9, 2015

Sept. 9, 2015

Hi, i am doing task 2 of eudyptula, i cloned the repository, build, install and boot the kernel, when i send my response to little i attach the uname -a output and the .config but he answers this: Linus's tree is newer than this, or you forgot to set the requested configuration option :( atm i get this kernel version: 4.2.0-rc8 i dont know if i am doing something wrong.Thanks

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linux aslr entropy bits
by 慕冬亮 Sept. 8, 2015

Sept. 8, 2015

Rs: number of bits randomized in the stack area, Rm: number of bits randomized in the mmap() area, Rx: number of bits randomized in the main executable area What's those three parameters? And how to calculate the aslr entropy bits? - mudongliang

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How to get the dentry value - no path_lookup
by Pria Mn Sept. 7, 2015

Sept. 7, 2015

Hi, I happened to come across the below discussion. http://lists.kernelnewbies.org/pipermail/kernelnewbies/2012-August/005914.h… I am having a similar issue. I am using Rhel7-3.10.0-123 kernel. I tried all the options that are mentioned above and none of the api's including kern_path() return valid dentry value. My requirement is to fetch directory name from filepath. Can anybody suggest a work-around for this ?

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