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a question about btfixupprep
by Chan Kim April 29, 2014

April 29, 2014

Hi, in arch/sparc/boot/Makefile, there is a rule below. $(obj)/btfix.S: $(obj)/btfixupprep vmlinux FORCE $(call if_changed,btfix) This makes btfix.S file using btfixupprep executable. and from the definition below, quiet_cmd_btfix = BTFIX $@ cmd_btfix = $(OBJDUMP) -x vmlinux | $(obj)/btfixupprep > $@ I can see to make the btfix.S, the make runs objdump -x vmlinux | btfixupprep > btfix.S What does btfixupprep do? maybe relocations? or function name substitution(for sub architecture)? Regards, Chan

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Re: [Kernel-BR] Re: [RFC] Only a.out QMAGIC format is working
by Geyslan Gregório Bem April 28, 2014

April 28, 2014

Andi, Em 28 de abril de 2014 00:23, Andi Kleen <andi(a)firstfloor.org> escreveu: > Geyslan Gregório Bem <geyslan(a)gmail.com> writes: > > > > There should be chance to fix it. > > > > I think it too. > > If it's randomization the following could help: > > echo 0 > /proc/sys/kernel/randomize_va_space > > Does it? > Nop. After this: $ echo 0 | sudo tee /proc/sys/kernel/randomize_va_space NMAGIC segfault and the others have been killed. > -Andi > > -- > ak(a)linux.intel.com -- Speaking for myself only > > -- > Você está recebendo esta mensagem porque se inscreveu no grupo "Kernel > Brasil" dos Grupos do Google. > Para cancelar inscrição nesse grupo e parar de receber e-mails dele, envie > um e-mail para kernel-br%2Bunsubscribe(a)googlegroups.com. > Para postar neste grupo, envie um e-mail para kernel-br(a)googlegroups.com. > Para ver esta discussão na web, acesse > https://groups.google.com/d/msgid/kernel-br/8738gym90x.fsf%40tassilo.jf.int… > . > Para obter mais opções, acesse https://groups.google.com/d/optout. > -- Regards, Geyslan G. Bem hackingbits.com

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Re: [Kernel-BR] Re: [RFC] Only a.out QMAGIC format is working
by Geyslan Gregório Bem April 28, 2014

April 28, 2014

Em 20 de abril de 2014 08:45, Pavel Machek <pavel(a)ucw.cz> escreveu: > On Sat 2014-04-19 13:37:27, Geyslan Gregório Bem wrote: > > Pavel, > > > > Thank you. > > > > Maintainers, is there some chance to fix it or a.out is really > > doomed? > > There should be chance to fix it. > > I think it too. > Do you have some idea when it stopped working? > But I have no clue when it stopped. > Pavel > -- > (english) http://www.livejournal.com/~pavelmachek > (cesky, pictures) > http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html > > -- > Você está recebendo esta mensagem porque se inscreveu no grupo "Kernel > Brasil" dos Grupos do Google. > Para cancelar inscrição nesse grupo e parar de receber e-mails dele, envie > um e-mail para kernel-br%2Bunsubscribe(a)googlegroups.com. > Para postar neste grupo, envie um e-mail para kernel-br(a)googlegroups.com. > Para ver esta discussão na web, acesse > https://groups.google.com/d/msgid/kernel-br/20140420114501.GA12135%40amd.pa… > . > Para obter mais opções, acesse https://groups.google.com/d/optout. > -- Regards, Geyslan G. Bem hackingbits.com

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how BTFIXUP_CALL is used..
by Chan Kim April 27, 2014

April 27, 2014

Hi, It's raining Suday afternoon in Korea where many people are in grief for the loss of their family members from the ferry accident last week. We have those victims and families in our thoughts and prayers.. Anyway, I have a question.. In file mm/memory.c (linux 3.3), in funrcion __pmd_alloc, I see a line below. pmd_t *new = pmd_alloc_one(mm, address); pmd_alloc_one is defined as below. #define pmd_alloc_one(mm, address) BTFIXUP_CALL(pmd_alloc_one)(mm, address) if I apply the BTFIXUP_CALL macro, (#define BTFIXUP_CALL(__name) ___f_##__name) it just becomes ___f_pmd_alloc_one which is defined in file arch/sparc/boot/btfix.S below. ----------- ... .global ___btfixup_end ___btfixup_end: ! Define undefined references .global ___f_flush_sig_insns ___f_flush_sig_insns: ... .global ___f_pmd_alloc_one ___f_pmd_alloc_one: ... --------------- which makes me think ___f_pmd_alloc_one is just an adress shared by many ___f_... functions. And I couldn't find ___f_pmd_alloc_one anywhere else. (no definition..) But actually, as I guessed, the pmd_alloc_one function is actually srmmu_pmd_alloc_one function. How is this done? I only know BTFIXUP.. thing is adjusting the functions for the correct subarchitecture but I can't understand how this is done. Could anyboy tell me how this is done? or any good reference? Thanks, Chan

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Buffer cache mechanism
by Satheesaran April 26, 2014

April 26, 2014

Hi All, I was reading through the text, "The Design of the Unix Operating System" - Maurice Bach While reading through the Buffer cache, I had the following query Buffer data structure, has Buffer header + pointer to data area + pointers for Buffer Management. Does this,"pointer to data area", corresponds to disk block or Logical Filesystem block ? I am confused about this. To add more, I am aware of the fact that disk block is of 512 bytes on the most of the hard disks and logical disk block size ( depending on filesystem ) is of 4k in size. what would be available in data area pointed in buffer ? Thanks, Satheesaran

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RE: Learning to write kernel modules
by Rahul Sharma April 25, 2014

April 25, 2014

Hi narendra, There are many books. What I feel to consider for hands on writing kernel modules yo can refer Linux Device Driver by JONATHAN CORBET, ALESSANDRO RUBINI & GREG KROAH-HARTMAN. Thanks, Rahul -----Original Message----- From: "Narendra Joshi" <narendraj9(a)gmail.com> Sent: ‎25/‎4/‎2014 8:14 PM To: "Kernelnewbies(a)kernelnewbies.org" <Kernelnewbies(a)kernelnewbies.org> Subject: Learning to write kernel modules Can someone suggest some resources for learning to write kernel modules for 3.x linux kernels? -- narendra _______________________________________________ Kernelnewbies mailing list Kernelnewbies(a)kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

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Where should I ask about USB Target code?
by Larry Martin April 25, 2014

April 25, 2014

I am developing a USB print capture device based on Gumstix Overo (TI OMAP) and the Gadget printer driver in Linaro 3.5.0 distribution. It looks like the distributed gadget driver may not be responding to USB Setup messages. I have used printk to verify that my data is correct when function composite_setup returns, but it does not appear on my Beagle 12 USB analyzer. I have not changed anything lower down than composite.c. Reading the code in usb/core is not helping much. I really want to trace the call stack from composite_setup back to the silicon, but cannot find where the .setup method of the composite driver is called. So my newbie question is, where do I go to find people who are into this part of the kernel and talk it over with them? Thanks, Larry

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Learning to write kernel modules
by Narendra Joshi April 25, 2014

April 25, 2014

Can someone suggest some resources for learning to write kernel modules for 3.x linux kernels? -- narendra

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Kworker and jbd2 constantly writing to hdd
by Jay Aurabind April 25, 2014

April 25, 2014

Hi, My kernel is 3.13.0-24, ubuntu 14.04. I have an ext4 root partition, and I can see 2 threads (kworker,jbd2) periodically writing to hdd at about roughly (1,5) second interval. I disabled journalling so that jbd2 is gone. Still, the kworker thread is bugging me. Is it really necessary for the system to work properly? cat /proc/<PID>/stack of the kworker is: [<ffffffff810846f1>] worker_thread+0x1d1/0x410 [<ffffffff8108b312>] kthread+0xd2/0xf0 [<ffffffff8172637c>] ret_from_fork+0x7c/0xb0 [<ffffffffffffffff>] 0xffffffffffffffff It doesnt make any sense to me. On tracing this kworker, I found this line: kworker/u8:1-68 [000] d... 1135.724955: workqueue_queue_work: \ work struct=ffff8800701e00b8 function= \ ata_sff_pio_task workqueue=ffff880073e6f600 req_cpu=256 cpu=0 So it seems the function ata_sff_pio_task in drivers/ata/libata-sff.c#L1343 is being run. Why is it getting called periodically? Is it possible to suppress it ? Someone else has also posted about it in arch linux forum: https://bbs.archlinux.org/viewtopic.php?id=178632, smelling a kernel bug. But I dont feel it could be a bug, because some other kernel thread must be requesting some operation, which could be the reason for a "generic" ata code to pop up. I'm concerned because my harddisk heats up unnecessarily (though not violently), and I never had such a situation while using windows (couple of years ago). I am a noob when it comes to kernel programming, (just started ldd3), so please correct me if I'm wrong. Please also suggest something to fix this issue, or to investigate more into this. Thanks and Regards, Jay

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Re: cgroups: cannot write on file memory.oom_control
by Hedi Boufaied April 25, 2014

April 25, 2014

Hi Rami, I have looked at the example code in your slides and wrote something similar to handle the OoM condition and it seems to work fine. Thank you for that. Since it would be even better for me to avoid playing with OoM, I explored another option for monitoring memory usage: keeping the OoM killer enabled and using the "memory threshold" feature (see below) to get notified when a group's memory usage exceeds the limit. First, my C code for monitoring the memory usage looked like this (running as a separate process): // Assuming that initial memory usage is below the threshold while(1) { if (read(efd, &counter, sizeof(uint64_t)) != sizeof(uint64_t)) die("read eventfd"); printf("Event received: memory usage ABOVE limit\n"); if (read(efd, &counter, sizeof(uint64_t)) != sizeof(uint64_t)) die("read eventfd"); printf("Event received: memory usage BELOW limit\n"); } Then I thought: what happens if mem usage crosses the threshold more than once between 2 consecutive calls to read() ? (a scenario that cannot be formally excluded). I realised that in this situation the "counter" value returned by read() would contain the number of occurrences crossing events. So for example if, between 2 calls to read(), the memory usage goes beyond then below the threshold, the value of "counter" after the 2nd read will be 2. I ended up using this counter behaviour to determine if the current usage is below or beyond the limit: counter = 0; above_mem_limit = 0; while(1) { if (read(efd, &counter, sizeof(uint64_t)) != sizeof(uint64_t)) die("read eventfd"); if(counter%2) above_mem_limit = !above_mem_limit; printf("Event received! (counter=%d), above_mem_limit=%d\n", counter, above_mem_limit); } My question: I have never seen this "event counter" behaviour documented anywhere. The cgroups docs and forums do not say anything about the 64bit value returned by the read() call. Do you think one can safely rely on this to count the number of crossing events ? Thanks and Regards, Hedi ---- From https://www.kernel.org/doc/Documentation/cgroups/memory.txt: 9. Memory thresholds Memory cgroup implements memory thresholds using the cgroups notification API (see cgroups.txt). It allows to register multiple memory and memsw thresholds and gets notifications when it crosses. To register a threshold, an application must: - create an eventfd using eventfd(2); - open memory.usage_in_bytes or memory.memsw.usage_in_bytes; - write string like "<event_fd> <fd of memory.usage_in_bytes> <threshold>" to cgroup.event_control. Application will be notified through eventfd when memory usage crosses threshold in any direction. It's applicable for root and non-root cgroup. ---- Best Regard, Hedi From: Hedi Boufaied/NCE/AMADEUS To: Rami Rosen <roszenrami(a)gmail.com>@AMAEXTMAIL_MUC, Cc: kernelnewbies <kernelnewbies(a)kernelnewbies.org> Date: 22/04/2014 13:12 Subject: Re: cgroups: cannot write on file memory.oom_control Hi Rami, Thank you for the advice. Yes, I will try using the event handler. Best Regards, Hedi From: Rami Rosen <roszenrami(a)gmail.com> To: Hedi Boufaied <hedi.boufaied(a)amadeus.com>, Cc: kernelnewbies <kernelnewbies(a)kernelnewbies.org> Date: 18/04/2014 22:38 Subject: Re: cgroups: cannot write on file memory.oom_control Sent by: kernelnewbies-bounces(a)kernelnewbies.org Hi Hedi, Well, you can use disabling oom in conjunction with event handler. Thus, you can free memory by changing memory setting of other cgroups when an oom occurs in a specific cgroup, and avoid having an oops in that cgroup. You can see an example of using event handler in conjunction with disabling the oom killer in "Namespaces and cgroups in linux", in slides 101/102, see: http://ramirose.wix.com/ramirosen A shameless plug - I wrote this presentation of 121 slides about namespaces and cgroups. Regards, Rami Rosen בתאריך 17 באפר 2014 11:24, "Hedi Boufaied" <hedi.boufaied(a)amadeus.com> כתב: Hi Rami, Thanks a lot for your sequence. I followed it and it does work. I now see my process paused in sleep state instead of getting killed when the cgroup reaches OoO. This being said: * I do not really understand why the use_hierarchy option needs to be disabled in order to allow disabling of the oom killer... * I'm not sure that disabling the OoO killer is safe/reliable enough: in some of the trials I made, I saw other processes (xterms) not part of the OoO cgroup getting completely stuck and I had to reboot my machine... Best Regards, Hedi From: Rami Rosen <roszenrami(a)gmail.com> To: Hedi Boufaied <hedi.boufaied(a)amadeus.com>, Cc: kernelnewbies <kernelnewbies(a)kernelnewbies.org> Date: 15/04/2014 15:39 Subject: Re: cgroups: cannot write on file memory.oom_control Hi, Hedi, This sequence works for me: echo 0 > /sys/fs/cgroup/memory/memory.use_hierarchy mkdir /sys/fs/cgroup/memory/0 Then, the following two commands changes the value of oom_kill_disable: echo 1 > /sys/fs/cgroup/memory/0/memory.oom_control echo 0 > /sys/fs/cgroup/memory/0/memory.oom_control For more info, please look for the text about enabling/disabling use_hierarchy in section 6, http://lxr.free-electrons.com/source/Documentation/cgroups/memory.txt. Regards, Rami Rosen http://ramirose.wix.com/ramirosen On Mon, Apr 14, 2014 at 12:22 PM, Hedi Boufaied <hedi.boufaied(a)amadeus.com> wrote: > Hi everyone, > > I am working with cgroups on OpenSuse (over VirtualBox) and I cannot disable > the OOM killer by writing to the file memory.oom_control: > >> echo 1 > memory.oom_control >> -bash: echo: write error: Invalid argument > > I can change the memory limit and several other settings by writing to the > appropriate files (like memory.limit_in_bytes) but I could never write to > file memory.oom_control although I am root. > > I saw someone posted a similar issue a few days ago but there was no > reply... > > I have copied below the sequence of command I am using. Any idea what could > be the issue ? > > Thanks in advance for your help! > > Hedi > > > ---- > > /sys/fs> su - root > > /sys/fs> cd cgroup > > /sys/fs/cgroup> cgcreate -g memory:/mygroup > > /sys/fs/cgroup> cd memory/mygroup > > /sys/fs/cgroup/memory/mygroup> echo 32M > memory.limit_in_bytes > > /sys/fs/cgroup/memory/mygroup> cat memory.limit_in_bytes > 33554432 > > /sys/fs/cgroup/memory/mygroup> echo 1 > memory.oom_control > -bash: echo: write error: Invalid argument > > /sys/fs/cgroup/memory/mygroup> cat memory.oom_control > oom_kill_disable 0 > under_oom 0 > > --- > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies(a)kernelnewbies.org > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > _______________________________________________ Kernelnewbies mailing list Kernelnewbies(a)kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

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