May 2011 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

is it safe to call spin_lock_bh() from within a soft IRQ?
by Jeff Haran May 26, 2011

May 26, 2011

My understanding is that if you have a critical data structure that is accessed in both process context and soft IRQ context on an SMP system, you can serialize access to it by using a spin lock. I also understand that to acquire such a spin lock from process context, you should use spin_lock_bh() because that will disable bottom halves on that CPU and thus prevent a dead lock that could otherwise occur if your process context code took the lock and then a software IRQ was run which attempt to acquire the same lock. What I have yet to find in the available documentation is whether in this scenario it would be safe to call spin_lock_bh() to acquire the lock from code that executes in soft IRQ context. I suspect such a practice is not advisable because it's not strictly necessary. Calling spin_lock() from the soft IRQ context code and calling spin_lock_bh() from the process context code would be most efficient because there is no need to disable bottom halves if you are already executing in soft IRQ context. But the inefficiency issue aside, can calling spin_lock_bh() from soft IRQ context cause other more serious problems like lock ups, data corruption, etc? The reason for the question is I am working on a kernel module that needs to take the same lock from both process and soft IRQ context and for the sake of modularity and simplicity I'd like to be able to use the same wrapper function to take the spin lock regardless of what context the code calling that function is executing in and am, at least for now, willing to accept a slight loss of performance due to disabling bottom halves when doing so is not strictly necessary. A corollary question would relate to taking read-write locks. Is it safe to call read_lock_bh() or write_lock_bh() from a soft IRQ? Thanks.

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CPU instruction to calculate tcp checksum and udp integrity?
by Jon Zhou May 26, 2011

May 26, 2011

hi now I am using sw to calculate the tcp checksum, is there CPU(nehalem) instruction or NIC /kernel API to do such thing? thanks a lot jon

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Self modifying code in ARM 11 architectures
by Ashok Babu May 26, 2011

May 26, 2011

Hi All, I am no success in booting up the ARM1176 processor with the linux-2.6.32 kernel. While googling about the ARM Harvard architecture, I came to know that we have to flush/invalidate the D-Cache and I-Cache when using the self modifying codes. So here my questions/doubts : 1) Is'nt it the kernel itself is self modifying code with lots of function pointers ? If yes, how is synchronization b/w d-cache and i-cache handled in the kernel ? 2) Can this be the reason for the kernel not booting for me ? Because If i disable the I-Cache in the config, then the kernel boots up without any issues. Any pointers on this will be of great help. Thanks & Best Regards Ashok

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how to run MMC tests on my ubuntu laptop?
by Robert P. J. Day May 25, 2011

May 25, 2011

probably a simple question but i'd like to play with the MMC driver; in particular, i want to experiment with the mmc_test module on my ubuntu laptop if that's possible. i've configured the kernel so that i have a loadable mmc_test module and i can certainly load and unload it, and i found what looks like a coherent example of its use here: http://us.generation-nt.com/answer/patch-mmc-test-move-files-sysfs-debugfs-… the problem *seems* to be that, when i insert an SD card into the slot on my ubuntu laptop, what shows up in /var/log/messages is: May 25 10:41:50 lynx kernel: [44208.051370] usb 1-1.1: new high speed USB device number 9 using ehci_hcd May 25 10:41:50 lynx kernel: [44208.177928] scsi10 : usb-storage 1-1.1:1.0 May 25 10:41:51 lynx kernel: [44209.173498] scsi 10:0:0:0: Direct-Access Generic- Multi-Card 1.00 PQ: 0 ANSI: 0 CCS May 25 10:41:51 lynx kernel: [44209.174871] sd 10:0:0:0: Attached scsi generic sg2 type 0 May 25 10:41:52 lynx kernel: [44210.332466] sd 10:0:0:0: [sdb] 7729152 512-byte logical blocks: (3.95 GB/3.68 GiB) May 25 10:41:52 lynx kernel: [44210.333320] sd 10:0:0:0: [sdb] Write Protect is off May 25 10:41:52 lynx kernel: [44210.339425] sdb: sdb1 sdb2 sdb3 May 25 10:41:52 lynx kernel: [44210.341786] sd 10:0:0:0: [sdb] Attached SCSI removable disk May 25 10:41:53 lynx kernel: [44210.846189] EXT3-fs: barriers not enabled May 25 10:41:53 lynx kernel: [44210.847598] kjournald starting. Commit interval 5 seconds May 25 10:41:53 lynx kernel: [44210.866802] EXT3-fs (sdb2): using internal journal May 25 10:41:53 lynx kernel: [44210.866810] EXT3-fs (sdb2): mounted filesystem with ordered data mode ... snip ... so that, clearly, this linux 2.6.39+ kernel sees the device as SCSI, handled by the usb-storage driver. under the circumstances, how would i (if it's even possible) access the card at the level necessary to run things like MMC tests? obviously, i would first unmount the two filesystems on it since those tests are destructive. but i've loaded the mmc_test module and inserted the card, and i don't see the appropriate subdirectory under /sys/kernel/debug. would someone with MMC/SD experience point me in the right direction as to how to start accessing the card at the driver level from user space, given my situation above? thanks. rday -- ======================================================================== Robert P. J. Day Ottawa, Ontario, CANADA http://crashcourse.ca Twitter: http://twitter.com/rpjday LinkedIn: http://ca.linkedin.com/in/rpjday ========================================================================

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Get log for panic
by Yermandu Patapitafious May 25, 2011

May 25, 2011

Hi all, I'm looking some way to get kernel log from boot panic. Maybe I'm wrong but is possible collect this info local? I search for remote collect in google, i try some ways but not successful. My notebook doesn't come with modem, so i think in use some local way or over Ethernet. How i can get this log? -- yermandu

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knewbies project? - updating LDD3 source
by Jim Cromie May 25, 2011

May 25, 2011

over at http://code.google.com/p/ldd3/ it says: The famous "Linux Device Drivers" released the sample code. but the code does not reflect the latest kernel updates, some of code cannot even compile. This project is to make it compatible with the current kernel. http://lwn.net/Kernel/LDD3/ http://examples.oreilly.com/9780596005900/ Neither the OReilly tarball, nor the googlecode's svn repo will compile for me on an updated F-14 box, neither against uname -r, or a local git-tree. So I pulled the svn-tree, and made these changes. I got a fair way to getting things to compile. Changes are quick-n-dirty, and some may be wrong, esp around workqueue stuff - I pretty much did what compiler told me, w/o any analysis. I didnt even get compilation on the aio/iovec users, on the changes from 2003. I havent really gotten my head around the whole conversion strategy; I know a loop over iovec elements is probably needed, but Im unclear where it should be. and Im unsure whether these functions are now cluttering up things. static void sculld_do_deferred_op(void *p) static int sculld_defer_op(int write, struct kiocb *iocb, const struct iovec *iov, size_t count, loff_t pos) I guess the point is Ive run out of time now, and am hoping for a dose of clarity, and further patches, to get LDD3 source compiling, up-to-date, and reflecting current best practices. GRUMBLING: its annoying that the googlecode web-page obfuscates the site owner, making it impossible to reach him. Username: guanzhi1...@gmail.com Is there another LDD3 repo somewhere, that a google search didnt reveal to me ? perhaps on kernel.org ?? Should there be ? Im attaching my svndiff, in hte hopes that folks here will apply it and improve upon it. thanks ~jimc

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Re: knewbies project? - updating LDD3 source (Jim Cromie)
by Vikram Narayanan May 24, 2011

May 24, 2011

> over at http://code.google.com/p/ldd3/ > it says: > The famous "Linux Device Drivers" released the sample code. but the > code does not reflect the latest kernel updates, some of code cannot > even compile. This project is to make it compatible with the current > kernel. > > http://lwn.net/Kernel/LDD3/ > http://examples.oreilly.com/9780596005900/ > > Neither the OReilly tarball, nor the googlecode's svn repo will compile for me > on an updated F-14 box, neither against uname -r, or a local git-tree. > > So I pulled the svn-tree, and made these changes. > I got a fair way to getting things to compile. > Changes are quick-n-dirty, and some may be wrong, > esp around workqueue stuff - I pretty much did what compiler told me, > w/o any analysis. > > I didnt even get compilation on the aio/iovec users, on the changes from 2003. > I havent really gotten my head around the whole conversion strategy; > I know a loop over iovec elements is probably needed, > but Im unclear where it should be. > > and Im unsure whether these functions are now cluttering up things. > > static void sculld_do_deferred_op(void *p) > static int sculld_defer_op(int write, struct kiocb *iocb, const struct > iovec *iov, > size_t count, loff_t pos) > > I guess the point is Ive run out of time now, and am hoping for a dose > of clarity, and further patches, to get LDD3 source compiling, up-to-date, > and reflecting current best practices. > > > GRUMBLING: its annoying that the googlecode web-page obfuscates the > site owner, making it impossible to reach him. > > Username: guanzhi1...@gmail.com You can actually see the mail ID. click on the dots and it will ask for a captcha and it will be revealed. Try that. - Thanks, Vikram

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Problem registering the Platform ADC driver
by conn intel May 24, 2011

May 24, 2011

Dear Friends, I am having issue with registering the platform device driver for ADC. http://pastebin.com/Ym1NTkfL - Link contains the snip code of kernel platform device and driver registration code . I have build the driver as module. When I load the driver as module, the probe function is not called from the driver. Can any one suggest what is missing in the code? I tried to find and study over internet about how to create platform device driver but in vain. Output: # insmod adc_at91.ko <8>Under at91_adc_init # rmmod adc_at91.ko <8>Under at91_adc_exit Thank you, Ankur.

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pid_task function fails to execute
by conn intel May 24, 2011

May 24, 2011

Hello friends, I am having issue with the pid_task function with arguments first as userspace pid (using getpid fn) and 2nd argument PIDTYPE_PID. "pid_task(<pid from userspace>, PIDTYPE_PID);" Can anyone assist me what can be the cause? Have a Good Day, Thank you, Ankur. *The kernel gives exception as below:* Unable to handle kernel NULL pointer dereference at virtual address 000001dd pgd = c7c04000 [000001dd] *pgd=779fe031, *pte=00000000, *ppte=00000000 Internal error: Oops: 1 [#1] last sysfs file: /sys/devices/platform/i2c-gpio.1/i2c-1/1-0048/temp1_pid <8>Modules linked in: tmp102 <8>CPU: 0 Tainted: G W (2.6.33.2 #100) <8>PC is at pid_task+0x18/0x44

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How to use the cryptographic API (e.g. md5 checksum)?
by Arvid Brodin May 23, 2011

May 23, 2011

Hi, I want to perform an md5 checksum on a process' text segment (I create a file /proc/<pid>/text_checksum that, when read, should give the md5sum). The crypto api documentation (Documentation/crypto/api-intro.txt) seems to be quite lacking. The only example is: tfm = crypto_alloc_hash("md5", 0, CRYPTO_ALG_ASYNC); if (IS_ERR(tfm)) fail(); /* ... set up the scatterlists ... */ desc.tfm = tfm; desc.flags = 0; if (crypto_hash_digest(&desc, sg, 2, result)) fail(); crypto_free_hash(tfm); Looking at some existing code, I see usage of crypto_hash_init(), crypto_hash_final(), desc.flag set to CRYPTO_TFM_REQ_MAY_SLEEP, ... (e.g. in fs/ecryptfs/crypto.c). Does anybody know what they do? Do I need to, or should I, use them? The functions are are declared in include/linux/crypto.h as some kind of wrapper functions, but lack documentation. Also, Google has not been my friend here. Thanks, Arvid Brodin Enea Services Stockholm AB

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