December 2010 - kernelnewbies@kernelnewbies.org

Problem with booting newly compiled kernel
by Prasad Joshi Dec. 22, 2010

Dec. 22, 2010

Hello, I seem to be always getting stuck in the new kernel booting. The problem is with mounting of the root file system. I don't have the log of the messages but, I guess, these were the messages reported VFS: Cannot open root device ............ Please append a correct "root=" boot option; here are the available partitions: Device: sda driver: sd ....... list of all partitions on sda, including correct size, offset of each parition ....... Device sdb driver: sr Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) Backtrace: It reported the correct list of sda partitions, including the driver name as sd. I have a SATA disk and the root partition has ext4 file system. The ext2/3/4 code is compiled as a part of the kernel. $ df -kh / Filesystem Size Used Avail Use% Mounted on /dev/sda1 459G 13G 423G 3% / As far as I can understand, as it is showing the correct list of partitions, the problem is not with the block device driver. But I am not sure, why it is failing to mount the file system when ext4 is also part of the kernel. grub.cfg file. menuentry 'Ubuntu, with Linux 2.6.37-rc6+' --class ubuntu --class gnu-linux --class gnu --class os { recordfail insmod part_msdos insmod ext2 set root='(hd0,msdos5)' search --no-floppy --fs-uuid --set ab9dfe8f-8e58-43ca-b16f-a42e0f02da72 linux /vmlinuz-2.6.37-rc6+ root=UUID=01432597-18e7-4609-9f85-3fad1d762ddc ro iommu=1 initrd /initrd.img-2.6.37-rc6+ } menuentry 'Ubuntu, with Linux 2.6.35-22-generic' --class ubuntu --class gnu-linux --class gnu --class os { recordfail insmod part_msdos insmod ext2 set root='(hd0,msdos5)' search --no-floppy --fs-uuid --set ab9dfe8f-8e58-43ca-b16f-a42e0f02da72 linux /vmlinuz-2.6.35-22-generic root=UUID=01432597-18e7-4609-9f85-3fad1d762ddc ro iommu=1 quiet splash initrd /initrd.img-2.6.35-22-generic } The kernel 2.6.35-22-generic boots correctly. Thanks and Regards, Prasad

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Re: A query on page cache and writepage
by Shreyansh Jain Dec. 21, 2010

Dec. 21, 2010

Hi Prasad, (My comment inline) On Sat, Dec 18, 2010 at 5:24 PM, Rajat Sharma <fs.rajat(a)gmail.com> wrote: > I am not sure if memory what for your filesystem needs mapping, may be to > support binary execution. Do you really need to support Writable or Shared > memory mappings? If you are good with Read-only mappings or Private memory > mapping (which does not modify data in page cache but modify a temporary > COWed copy), the solution is simple - do not implement writepage method at > all, there won't be any dirty data in page cache at any point of time, so no > need to flush page cache, however you need to discard page cache range when > you modify the file through f_op->write(), otherwise memory mapped files > will read stale data. > > Rajat > > On Sat, Dec 18, 2010 at 6:51 AM, Prasad Joshi <prasadjoshi124(a)gmail.com> > wrote: >> >> Hello All, >> >> I am working on a file system, that uses page cache only if a file is >> memory mapped. This is how the code is designed >> >> write() >> { >> write the data onto the disk >> >> if (file not memory mapped) >> return; >> >> /* file is memory mapped */ >> while (till all data is not syced with page cache) { >> if (data at current file offset held in page) { >> update the page >> } >> } >> } >> >> The code that updates a page is something like this >> page = find_lock_page(mapping, index); >> if (likely(!page)) { >> /* page not cached */ >> continue; >> } >> >> if (mapping_writably_mapped(mapping)) >> flush_dcache_page(page); >> >> pagefault_disable(); >> >> /* copy the data */ >> BUG_ON(!in_atomic()); >> page_buf = kmap_atomic(page, KM_USER0); >> if (__copy_from_user_inatomic(page_buf+offset, user_buf, size)) { >> kunmap(page); >> unlock_page(page); >> err = -EFAULT; >> goto out_error; >> } >> kunmap_atomic(page_buf, KM_USER0); >> pagefault_enable(); >> >> flush_dcache_page(page); >> mark_page_accessed(page); >> >> SetPageUptodate(page); >> ClearPageError(page); >> unlock_page(page); >> page_cache_release(page); >> >> If a fops->write() is called the data in page cache is already on to >> the disk. I don't want a page update from this function to trigger >> writepage() function. >> >> The writepage() function should only be called if an user updates a >> memory mapped page. >> >> Would calling page_clear_dirty() from the write() code be sufficient? Are you sure that once you have cleared the dirty bit no other process mapping this file is performing any modifications? If yes, probably that should suffice. >> >> I need to call flush_dcache_page() as a page should be coherent with >> other mappings. Does calling flush_dcache_page() result in call to >> writepage()? I very faintly remember that flush_dcache_page would invoke the mmap operations which in turn would converge back into a filesystem specific writepage call. Hence, I would expect writepage to be called for dcache flush operation. Probably this might be helpful: http://lxr.linux.no/#linux+v2.6.36/Documentation/cachetlb.txt#L279 Also, had I been in your shoes, I would have actually put a printk like thing in my writepage operation to confirm if indeed my function was not getting called from any kernel specific threads (like pdflush etc). [Please take my suggestions with a pinch of salt as I have been out of touch with this topic since ages - and in case you find them incorrect, I would be very thankful in case you can correct me too] -- Shreyansh

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Re: writing boot loader
by vamidhar s Dec. 21, 2010

Dec. 21, 2010

processor -bcm53003 its mips 32 . i am planning to port linux 2.6.27. i got some reference code to builld cfe bootloader,but i dont know where to start in that code. bootloader has to perform these low level initialization Reset and ROM trap handler vectors • CPU and FPU initialization • L1 and L2 Cache initialization • Multiprocessor initialization • Memory controller initialization • PCI and LDT bus configuration • Environment variables • Console device initialization • Bootstrap device initialization On Fri, Dec 17, 2010 at 7:57 PM, Chaitannya Mahatme <chaitannya(a)gmail.com>wrote: > On Friday 17 December 2010 03:05 PM, Anuz Pratap Singh Tomar wrote: > > > > On Fri, Dec 17, 2010 at 8:46 AM, Mahatme <chaitannya(a)gmail.com> wrote: > >> Hi Vamidhar, >> >> >> You need to provide more information regarding your development. What >> bootloader you want to install / create depends on many factors >> >> 1. What is your target application. >> 2. Chip architecture : does it have MMU (most significant parameter) >> 3. Is there a bootloader existing for the architecture (u-boot / Grub >> / Lilo ) have ready made ports for lot of architectures. You would have to >> see if they already have done the development. >> 4. What OS you are planning to port.. or there is no OS to be >> installed. E.g. some bootloaders like u-boot are optimized for Linux >> kernel. >> >> Please answer to those question so that you would get more relevant >> answer. >> >> Chaitannya, > > its utterly rude to top post. Please don't do that.(read community > guidelines) > > its most likely Linux(if not, probably this in not the list for it), and > there were couple of mails where he did discuss about arch and detail. > > > > > Got your point... It's just that I am following this convention since past > 10 years (No one told me it was rude). > Also about the Vamidhar post I did not find any old reference. > > > -- > Cheers !!! > Chaitannya > > follow me on twitter http://twitter.com/chaitannya > > I believe there's a hero in all of us > who keeps us honest, gives us strength, makes us noble, and finally allows > us to die with pride, > even though sometimes we have to be steady, and give up the thing we want > the most... even our dreams. > - Spider Man 2 > -- To unsubscribe from this list: send an email with "unsubscribe > kernelnewbies" to ecartis(a)nl.linux.org Please read the FAQ at > http://kernelnewbies.org/FAQ

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Low on disk space after compiling new kernel.
by Rishi Agrawal Dec. 21, 2010

Dec. 21, 2010

Hi All, I installed the kernel 2.6.36 into my Fedora 12 system. I am now low on disk space. [root@rishi-desktop kernels]# du -sh linux-2.6.36/ 4.4G linux-2.6.36/ It shows that the new compiled kernel is taking around 4.4GB. The /lib/modules/2.6.36 is taking around 780M on my disk. I wanted to free some of the space occupied by the compiled code. I understand that the /lib/modules/2.6.36 directory can't be deleted as it contains the compiled modules. I wanted to delete the files in /usr/src/kernel/2.6.36, without effecting my newly installed kernel. -> Can I delete them? -> What is the best way to delete them, I want to keep the source files? -> Should I run make clean to remove the compiled code? -> Any other way? -- Regards, Rishi Agrawal

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Suggestion for the LISTDOMAIN
by Michelle Konzack Dec. 20, 2010

Dec. 20, 2010

Hello * and owners of <kernelnewbies.org>, since I am ISP I am runing into troubles with spam coming from listservers or faked Froms: I suggest you to CHANGE the LISTDOMAIN from kernelnewbies.org to lists.kernelnewbies.org which makes spamfiltering much easier. Thanks, Greetings and nice Day/Evening Michelle Konzack -- ##################### Debian GNU/Linux Consultant ###################### Development of Intranet and Embedded Systems with Debian GNU/Linux itsystems@tdnet France EURL itsystems@tdnet UG (limited liability) Owner Michelle Konzack Owner Michelle Konzack Apt. 917 (homeoffice) 50, rue de Soultz Kinzigstraße 17 67100 Strasbourg/France 77694 Kehl/Germany Tel: +33-6-61925193 mobil Tel: +49-177-9351947 mobil Tel: +33-9-52705884 fix <http://www.itsystems.tamay-dogan.net/> <http://www.flexray4linux.org/> <http://www.debian.tamay-dogan.net/> <http://www.can4linux.org/> Jabber linux4michelle(a)jabber.ccc.de Linux-User #280138 with the Linux Counter, http://counter.li.org/

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Suggestion for the LISTDOMAIN
by Michelle Konzack Dec. 20, 2010

Dec. 20, 2010

Hello * and owners of <kernelnewbies.org>, since I am ISP I am runing into troubles with spam coming from listservers or faked Froms: I suggest you to CHANGE the LISTDOMAIN from kernelnewbies.org to lists.kernelnewbies.org which makes spamfiltering much easier. Thanks, Greetings and nice Day/Evening Michelle Konzack -- ##################### Debian GNU/Linux Consultant ###################### Development of Intranet and Embedded Systems with Debian GNU/Linux itsystems@tdnet France EURL itsystems@tdnet UG (limited liability) Owner Michelle Konzack Owner Michelle Konzack Apt. 917 (homeoffice) 50, rue de Soultz Kinzigstraße 17 67100 Strasbourg/France 77694 Kehl/Germany Tel: +33-6-61925193 mobil Tel: +49-177-9351947 mobil Tel: +33-9-52705884 fix <http://www.itsystems.tamay-dogan.net/> <http://www.flexray4linux.org/> <http://www.debian.tamay-dogan.net/> <http://www.can4linux.org/> Jabber linux4michelle(a)jabber.ccc.de Linux-User #280138 with the Linux Counter, http://counter.li.org/

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add_timer crashes the kernel,Why?
by lijin liu Dec. 20, 2010

Dec. 20, 2010

Hello everyone! I want to use the timer in my kernel module. I read the book _Linux kernel development 3rd version_ and LDD 3rd version. Both the two books tell me write the code like this: struct timer_list my_timer; init_timer(&my_timer); my_timer.expires = jiffies + wait; my_timer.data = 0; my_timer.function=my_function; //active the timer: add_timer(&timer); When I insmod the module, the kernel crashed, and when I change my code to *mod_timer* rather than add_timer. It just works! But why the add_timer crash the kernel?

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Re: add_timer crashes the kernel,Why?
by lijin liu Dec. 20, 2010

Dec. 20, 2010

On Mon, Dec 20, 2010 at 4:42 PM, Raz <raziebe(a)gmail.com> wrote: > try to remove mytimer from stack Yes, I made a stupid mistake, It works now.

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Re: strncpy_from_user called from invalid context?
by Dave Hylands Dec. 20, 2010

Dec. 20, 2010

Hi Greg, On Sat, Dec 18, 2010 at 2:27 PM, Greg Kerr <kerrgi(a)gmail.com> wrote: > In order to learn the jprobes interface, I am a writing a fairly silly example > jprobe. However, I'm having issues copying a string from userspace.... > Basically somehow I wind up calling a function that may sleep from an invalid > context (interrupts disabled or something). > > I have the source of the function in question and the stack trace below. If > anyone could give me a few pointers it would be greatly appreciated. I'd get rid of the 1K stack variable. I think on x86, the kernel stack is only 4K. Use kmalloc instead. If your stack variable is crossing the page boundary and nothing is mapped into memory there, then that could cause the page fault. I'd also recommend using strlcpy rather than strncpy. See: <http://www.gratisoft.us/todd/papers/strlcpy.html> Your use of strncpy is incomplete. To be complete, you need to do: strncpy( dest, src, sizeof( dest )); dest[ sizeof( dest ) - 1 ] = '\0'; I'm not 100% sure about strncpy_from_user but with regular strncpy, if the length of the source is >= sizeof the destination, then your destination string won't be null terminated. And of course, you should make sure that the user-mode program passed in a valid pointer. -- Dave Hylands Shuswap, BC, Canada http://www.DaveHylands.com/

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Fwd: strncpy_from_user called from invalid context?
by Mulyadi Santosa Dec. 20, 2010

Dec. 20, 2010

Resending it to the new shiny mailing list address :D ---------- Forwarded message ---------- From: Mulyadi Santosa <mulyadi.santosa(a)gmail.com> Date: Sun, Dec 19, 2010 at 12:36 Subject: Re: strncpy_from_user called from invalid context? To: Greg Kerr <kerrgi(a)gmail.com> Cc: kernelnewbies(a)nl.linux.org Hi Greg.... let us see the basic situation first...since I am not an expert either... On Sun, Dec 19, 2010 at 05:27, Greg Kerr <kerrgi(a)gmail.com> wrote: > [ 421.250737] BUG: sleeping function called from invalid context at > arch/x86/mm/fault.c:1074 > [ 421.250742] in_atomic(): 0, irqs_disabled(): 1, pid: 1718, name: dmesg > [ 421.250745] Pid: 1718, comm: dmesg Not tainted 2.6.35.9-64.fc14.x86_64 #1 > [ 421.250748] Call Trace: > [ 421.250756] [<ffffffff8103d1d5>] __might_sleep+0xeb/0xf0 > [ 421.250761] [<ffffffff8146cbf4>] do_page_fault+0x15c/0x265 > [ 421.250765] [<ffffffff8146a075>] page_fault+0x25/0x30 > [ 421.250770] [<ffffffff8121db83>] ? strncpy+0xc/0x27 > [ 421.250774] [<ffffffffa000f049>] j_sys_open+0x37/0xc6 [exe_probe] I am not 100% sure if I "cut" the stack trace into the most relevant path, so let's just assume it is indeed correct. First, irqs_disabled = 1 makes me think that you probably hook into atomic code path. Before answering that, may we know, where do you put this hook anyway? at the sys_open() itself? or somewhere else? Second complication is that fairly likely, it retrieves file name (I hope I read your code correctly) from use memory area that might be swapped out. If it is the problem, then mlock() it could be the workaround. However, the solution might be non All in all, it's better to also write down the way you register the probe etc, that way we could have better understanding of your work, thus might pinpoint another root of the problem itself. PS: on a second thought, I am curious on why I see __do_fault in early "stage" of your back trace. Could it be that your code might be called during page fault itself? Thus it's something like: fault--> supposed to be atomic from here on-->read a portion of a file--> your probe called--> do something that blocks--> boom? -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com -- regards, Mulyadi Santosa Freelance Linux trainer and consultant blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com

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