August 2014 - kernelnewbies@kernelnewbies.org

Nick Krause page fault
by nayobix Aug. 15, 2014

Aug. 15, 2014

Guys, I just dont understand, why Nick Krause isn't still banned from this mailing list. This mailing list seems like some schizophrenia forum.... Regards, B. -- nayobix

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Trace Help
by Nick Krause Aug. 15, 2014

Aug. 15, 2014

I am just going to be blunt and assume that my trace is wrong. I am tracing the bug , https://bugzilla.kernel.org/show_bug.cgi?id=72291. Here are my trace steps 1.Start in _break_lease and find locks_insert_block and trace into that function 2. In that function we hit the internal function, _locks_insert_block and I trace into that function 3. When I trace into that function , I get see we are using the same spinlocks as the other functions and come to the conclusion we are not holding the right spinlock and are looping indefinitely 4. This comment , /* Must be called with i_lock held. */ seems to a value thing to check if we are holding the i_lock spinlock 5.I trace back to where we are calling in the function, _break_lease and we are calling like this, locks_insert_block(flock, new_fl); I known that flock is the lock that we are calling with and logically needs the i_lock 6. flock = inode->i_flock; is clearly not the right lock and we are already holding it in another spinlock as part of this function , spin_lock(&inode->i_lock); This means that we are looping forever trying to get the i_lock that is already held by another spinlock, causing us to loop forever when we call _break_lease. Nick

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Sparse fixes
by Lucas Tanure Aug. 15, 2014

Aug. 15, 2014

Hi, If I do : $ cat drivers/staging/android/TODO TODO: - checkpatch.pl cleanups - *sparse fixes* - rename files to be not so "generic" - make sure things build as modules properly - add proper arch dependencies as needed - audit userspace interfaces to make sure they are sane Please send patches to Greg Kroah-Hartman <greg(a)kroah.com> and Cc: Brian Swetland <swetland(a)google.com> *What are sparse fixes ? * *It's a tool to run in the kernel code ? * Thanks -- Lucas Tanure +55 (19) 988176559

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How to find the device address inside kernel
by Ulka Vaze Aug. 15, 2014

Aug. 15, 2014

Hi, I want to find the device address of scsi generic /dev/sg2 inside kernel. Is there any way to find that ? Any pointers are appreciated. Regards, -Ulka -- Director L2IT -Learn & Leverage Information Technology Leading Professional Training Institute in Pune www.l2it.com

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Skb Documentation?
by Nick Krause Aug. 15, 2014

Aug. 15, 2014

After searching around in the documentation directory, I need no information on skb data structure and other information relating to skb data type. If someone knowns where there is Documentation in the kernel directory please tell me, otherwise I would be glad to write up. Regards Nick

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usb_driver hotplug probe callback
by Jaret Flores Aug. 15, 2014

Aug. 15, 2014

I know I am not supposed to get too much help on the eudyptula challenges, but I can't seem to figure this last thing out. The goal is to write (the skeleton of) a usb driver module that loads and registers the driver when a usb keyboard is plugged in. What I have so far does exactly that except that the struct usb_driver: 1) probe function is not called (neither via keyboard plugin nor when module is loaded manually with modprobe). 2) disconnect function is called only after the module is unloaded (with rmmod) AND THEN the keyboard is unplugged. >From ldd3: for probe: "This function is called by the USB core when it thinks it has a struct usb_interface that this driver can handle." for disconnect: "This function is called by the USB core when the struct usb_interface has been removed from the system or when the driver is being unloaded from the USB core." >From the quotes, it seems the kernel does not think my driver is valid to handle the keyboard (though 2 may not actually be abnormal behavior). I am thinking, perhaps the struct usb_device_id table is wrong or incomplete: static struct usb_device_id hw_id_table[] = { {USB_INTERFACE_INFO(USB_INTERFACE_CLASS_HID, USB_INTERFACE_SUBCLASS_BOOT, USB_INTERFACE_PROTOCOL_KEYBOARD)}, {} }; MODULE_DEVICE_TABLE(usb, hw_id_table); There is also a USB_DEVICE_INFO() macro, but I cannot seem to find a file analogous to include/uapi/linux/hid.h which (would) define the arguments to USB_DEVICE_INFO(). Is this the problem? Or am I missing something else? Thanks for the info, Jaret

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Re: [PATCH] usb: Fix switch statement in ohci-tmio.c
by Nick Krause Aug. 15, 2014

Aug. 15, 2014

On Thu, Aug 14, 2014 at 2:05 PM, Nicholas Krause <xerofoify(a)gmail.com> wrote: > I am fixing the bug on at the link, https://bugzilla.kernel.org/show_bug.cgi?id=79931. > This bug report states that in the function, tmio_hc_stop the switch has no needed breaks. > Further more this patch fixes this bug by adding the needed breaks. > > Signed-off-by: Nicholas Krause <xerofoify(a)gmail.com> > --- > drivers/usb/host/ohci-tmio.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/usb/host/ohci-tmio.c b/drivers/usb/host/ohci-tmio.c > index bb40958..d2b5382 100644 > --- a/drivers/usb/host/ohci-tmio.c > +++ b/drivers/usb/host/ohci-tmio.c > @@ -100,12 +100,16 @@ static void tmio_stop_hc(struct platform_device *dev) > switch (ohci->num_ports) { > default: > dev_err(&dev->dev, "Unsupported amount of ports: %d\n", ohci->num_ports); > + break; > case 3: > pm |= CCR_PM_USBPW3; > + break; > case 2: > pm |= CCR_PM_USBPW2; > + break; > case 1: > pm |= CCR_PM_USBPW1; > + break; > } > tmio_iowrite8(0, tmio->ccr + CCR_INTC); > tmio_iowrite8(0, tmio->ccr + CCR_ILME); > -- > 1.9.1 > If someone wants to send out this patch for me,that would be great :). Nick

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[PATCH] usb: Fix switch statement in ohci-tmio.c
by Nicholas Krause Aug. 14, 2014

Aug. 14, 2014

I am fixing the bug on at the link, https://bugzilla.kernel.org/show_bug.cgi?id=79931. This bug report states that in the function, tmio_hc_stop the switch has no needed breaks. Further more this patch fixes this bug by adding the needed breaks. Signed-off-by: Nicholas Krause <xerofoify(a)gmail.com> --- drivers/usb/host/ohci-tmio.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/usb/host/ohci-tmio.c b/drivers/usb/host/ohci-tmio.c index bb40958..d2b5382 100644 --- a/drivers/usb/host/ohci-tmio.c +++ b/drivers/usb/host/ohci-tmio.c @@ -100,12 +100,16 @@ static void tmio_stop_hc(struct platform_device *dev) switch (ohci->num_ports) { default: dev_err(&dev->dev, "Unsupported amount of ports: %d\n", ohci->num_ports); + break; case 3: pm |= CCR_PM_USBPW3; + break; case 2: pm |= CCR_PM_USBPW2; + break; case 1: pm |= CCR_PM_USBPW1; + break; } tmio_iowrite8(0, tmio->ccr + CCR_INTC); tmio_iowrite8(0, tmio->ccr + CCR_ILME); -- 1.9.1

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Understanding page statistics
by Martin Ichilevici de Oliveira Aug. 14, 2014

Aug. 14, 2014

Hello, I'm starting to study and learn the kernel, and I'm particulary interested in the virtual memory mechanism and it's application in NUMA architectures. As far as I could understand, the kernel keeps track of some information/statistics about each page, and I'd like to read them with a kernel module - just to see what kind of information is available (something more detailed than /proc/<pid>/maps). In a LWN article [1], I read the following: "The scheduler will periodically scan through each process's address space, revoking all access permissions to the pages that are currently resident in RAM. The next time the affected process tries to access that memory, a page fault will result. The scheduler will trap that fault and restore access to the page in question; it will also increment an access counter in a per-process array indexed by the NUMA node number." I've built a simple kernel module that, given a PID and virtual address, retrieves the corresponding struct page. I'm now unsure now where to look for such statistics and counters. Any hints on relevant data structures are appreciated. Thank you, Martin [1] : http://lwn.net/Articles/568870/

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Questions about Kernel Memory that I didn't find answers in Google - Please Help
by Lucas Tanure Aug. 14, 2014

Aug. 14, 2014

Hi, I'm looking for some site, pdf, book etc, that can answer this questions. For now I have : http://unix.stackexchange.com/questions/5124/what-does-the-virtual-kernel-m… I want to understand a few things about the memory and the execution of Linux kernel. Taking from a X86 and grub I have: 1) Grub loads kernel and root file system in memory, and the vmlinux has the code to decompress it self, right ? linux 2) The address of load kernel is always the same ? And It's at compilation time that is chosen ? 2a) The kernel takes places in 3g-4g memory place, and user space from 0 to 3gb. But if the pc has only 256mb of memory ? And when pc has 16gb of memory, the user space will be split in two ? 2b) And if kernel has soo many modules that needs more than 1gb to run ? 2c) How we configure all of that memory configs ? make menuconfig and friends ? 3) The function A will call functon B. B is at 0xGGGGGG in .text section, but kernel was loaded in address 0xJJJJJJJJJJ, how A will find B ? 4) Please consider this: $ readelf -S -W vmlinux There are 37 section headers, starting at offset 0xe05718: Section Headers: [Nr] Name Type Address Off Size ES Flg Lk Inf Al [ 0] NULL 0000000000000000 000000 000000 00 0 0 0 [ 1] .text PROGBITS ffffffff81000000 200000 53129a 00 AX 0 0 4096 [ 2] .notes NOTE ffffffff8153129c 73129c 0001d8 00 AX 0 0 4 [ 3] __ex_table PROGBITS ffffffff81531480 731480 002018 00 A 0 0 8 [ 4] .rodata PROGBITS ffffffff81600000 800000 1655ee 00 A 0 0 64 [ 5] __bug_table PROGBITS ffffffff817655f0 9655f0 005424 00 A 0 0 1 [ 6] .pci_fixup PROGBITS ffffffff8176aa18 96aa18 002f88 00 A 0 0 8 [ 7] .tracedata PROGBITS ffffffff8176d9a0 96d9a0 00003c 00 A 0 0 1 [ 8] __ksymtab PROGBITS ffffffff8176d9e0 96d9e0 00e710 00 A 0 0 16 [ 9] __ksymtab_gpl PROGBITS ffffffff8177c0f0 97c0f0 00a150 00 A 0 0 16 [10] __kcrctab PROGBITS ffffffff81786240 986240 007388 00 A 0 0 8 [11] __kcrctab_gpl PROGBITS ffffffff8178d5c8 98d5c8 0050a8 00 A 0 0 8 [12] __ksymtab_strings PROGBITS ffffffff81792670 992670 01cb42 00 A 0 0 1 [13] __init_rodata PROGBITS ffffffff817af1c0 9af1c0 0000e8 00 A 0 0 32 [14] __param PROGBITS ffffffff817af2a8 9af2a8 000b00 00 A 0 0 8 [15] __modver PROGBITS ffffffff817afda8 9afda8 000258 00 A 0 0 8 [16] .data PROGBITS ffffffff81800000 a00000 0e1180 00 WA 0 0 4096 [17] .vvar PROGBITS ffffffff818e2000 ae2000 001000 00 WA 0 0 16 [18] .data..percpu PROGBITS 0000000000000000 c00000 015300 00 WA 0 0 4096 [19] .init.text PROGBITS ffffffff818f9000 cf9000 0503ea 00 AX 0 0 16 [20] .init.data PROGBITS ffffffff8194a000 d4a000 09e4c8 00 WA 0 0 4096 [21] .x86_cpu_dev.init PROGBITS ffffffff819e84c8 de84c8 000018 00 A 0 0 8 [22] .parainstructions PROGBITS ffffffff819e84e0 de84e0 00bd3c 00 A 0 0 8 [23] .altinstructions PROGBITS ffffffff819f4220 df4220 005f40 00 A 0 0 1 [24] .altinstr_replacement PROGBITS ffffffff819fa160 dfa160 001a69 00 AX 0 0 1 [25] .iommu_table PROGBITS ffffffff819fbbd0 dfbbd0 0000f0 00 A 0 0 8 [26] .apicdrivers PROGBITS ffffffff819fbcc0 dfbcc0 000020 00 WA 0 0 8 [27] .exit.text PROGBITS ffffffff819fbce0 dfbce0 0009bc 00 AX 0 0 1 [28] .smp_locks PROGBITS ffffffff819fd000 dfd000 005000 00 A 0 0 4 [29] .data_nosave PROGBITS ffffffff81a02000 e02000 001000 00 WA 0 0 4 [30] .bss NOBITS ffffffff81a03000 e03000 122000 00 WA 0 0 4096 [31] .brk NOBITS ffffffff81b25000 e03000 425000 00 WA 0 0 1 [32] .comment PROGBITS 0000000000000000 e03000 000027 01 MS 0 0 1 [33] .debug_frame PROGBITS 0000000000000000 e03028 002560 00 0 0 8 [34] .shstrtab STRTAB 0000000000000000 e05588 00018a 00 0 0 1 [35] .symtab SYMTAB 0000000000000000 e06058 1a29f8 18 36 43659 8 [36] .strtab STRTAB 0000000000000000 fa8a50 180d92 00 0 0 1 Key to Flags: W (write), A (alloc), X (execute), M (merge), S (strings), l (large) I (info), L (link order), G (group), T (TLS), E (exclude), x (unknown) O (extra OS processing required) o (OS specific), p (processor specific) So the vmlinux is loaded in memory like a dd ? 5) In my function A, inside the module that I wrote, a non-initialized variable will take place in non-initialized section that was loaded in memory ? Or my modules has a new sections for it's own use, and my module is loaded my memory like a process, with all his sections? So how another module or kernel code will fin my exported variable/function ? 6) Let's suppose: I have a int variable, with 17 as content, and the address is 0xGGGGGG. If I stop the linux in this time, read my memory at address 0xGGGGGG I will got 17, right ? 0xGGGGGGG will be bigger than 0xc0000000 always, right ? 7) Now take int from question and change for: struct mystruct * foo = (struct mystruct* ) kmalloc(sizeof(struct mystruct)); I will be able to read at address 0xGGGGGG the struct that created, and it address will be greater than 0xc0000000, right ? But for this struct, the memory will be allocated for ever, until I free the pointer, right ? Well, this just a start. I really want to understand how kernel is run, loaded etc. Any help is appreciate, answering my questions, links to read, books to read. Actually, I didn't find any book with that kind of information . -- Lucas Tanure +55 (19) 988176559

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