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Re: Kernelnewbies Digest, Vol 37, Issue 37
by Frank Martinez Dec. 28, 2013

Dec. 28, 2013

unsubscribe On Sat, Dec 28, 2013 at 12:00 PM, <kernelnewbies-request(a)kernelnewbies.org>wrote: > Send Kernelnewbies mailing list submissions to > kernelnewbies(a)kernelnewbies.org > > To subscribe or unsubscribe via the World Wide Web, visit > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > or, via email, send a message with subject or body 'help' to > kernelnewbies-request(a)kernelnewbies.org > > You can reach the person managing the list at > kernelnewbies-owner(a)kernelnewbies.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of Kernelnewbies digest..." > > > Today's Topics: > > 1. Re: Can't cleanly unload driver (Valdis.Kletnieks(a)vt.edu) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Sat, 28 Dec 2013 00:13:08 -0500 > From: Valdis.Kletnieks(a)vt.edu > Subject: Re: Can't cleanly unload driver > To: Eric Fowler <eric.fowler(a)gmail.com> > Cc: kernelnewbies(a)kernelnewbies.org > Message-ID: <221197.1388207588(a)turing-police.cc.vt.edu> > Content-Type: text/plain; charset="us-ascii" > > On Fri, 27 Dec 2013 19:33:50 -0800, Eric Fowler said: > > > I suspect I am doing something wrong in the code with > > register/unregister_chrdev(), but I have been over that code a million > > times. It looks fine. > > > > Now: > > insmod the device, OK > > rmmod the device, OK > > Check /proc/devices , device # is present > > insmod the device again, fails with ERROR: could not insert module > > ./foobar.ko: Device or resource busy > > It does smell like an unregister issue. You may want to try adding > printk() calls to print out the return code from register and unregister. > I'm willing to bet that (a) the unegister is failing because somebody > still has a reference on the device, and (b) the second register call fails > because the device already exists, causing your module_init() to bail out. > > The fun is that you may not have taken a reference on the device directly > yourself - you may have called some other get_foo() that ends up taking an > implicit reference under the covers, causing issues when you fail to call > put_foo() at the right place... >

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Query regarding physically discontiguous memory
by Pritam Bankar Dec. 26, 2013

Dec. 26, 2013

Hi, I just started reading Memory Managment chapter from book Professional Linux Kernel Architecture. At very start of chapter I came across terms FLATMEM, DISCONTIGMEM and SPARSEMEM. Out of these DISCONTIGMEM and SPARSEMEM are available to NUMA systens only. Book also says UMA systems can also choose DISCONTIGMEM option if there address space contains large holes. Some googling says DISCONTIGMEM is prefered when we have physical discontiguous memory. This is what I don't understand what does it mean by containing large holes? physical discontiguous memory? Is it like when I put 2 RAM chips in a system then memory for them will be discontiguous? Would /proc/iomem give me details I wanted? Per my understanding RAM memory will ALWAYS be contiguous whether its 512 MB or 4 GB. Please give me graceful example of discontiguous physical memory That will really help me out.

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how to use mmap() on a disk file to get a kernel address?
by Yu Bi Dec. 26, 2013

Dec. 26, 2013

Hi, I try to mmap a file in a linux kernel module. I have tried to use the function do_mmap_pgoff. But the address returned is memory virtual address in current process' user space, i.e., below the kernel boundary. Instead, I want to map the file in the kernel space and get the kernel virtual address of the mapped region. Is there any kernel API in Linux support this operation? Or I have to reimplement a kernel mmap version ? But reimplement a kernel version mmap() is not easy I guess. Do you have any idea?

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MPC8641 based custom board kernel Bug
by Ashish Khetan Dec. 26, 2013

Dec. 26, 2013

Hi, I was trying to port Linux-3.12 for MPC8641 based custom designed board for evaluation purpose. I have been facing a kernel bug at mpic initialization. Is somebody have faced this kind of bugs or can give me any pointer for further steps how to solve kernel bugs will be really helpful. here is the snapshot for the bug that may be helpful to address the bug. Using MPC86xx HPCN machine description Total memory = 512MB; using 1024kB for hash table (at cff00000) Linux version 3.12.0 (ashish@ashish-VirtualBox) (gcc version 4.7.2 (GCC) ) #2 We d Dec 25 16:04:36 IST 2013 Found initrd at 0xde975000:0xdfec428a bootconsole [udbg0] enabled setup_arch: bootmem mpc86xx_hpcn_setup_arch() MPC86xx HPCN board from Freescale Semiconductor arch: exit Zone ranges: DMA [mem 0x00000000-0x1fffffff] Normal empty HighMem empty Movable zone start for each node Early memory node ranges node 0: [mem 0x00000000-0x1fffffff] Built 1 zonelists in Zone order, mobility grouping on. Total pages: 130048 Kernel command line: root=/dev/ram0 rw rootfs console=ttyS0,115200 PID hash table entries: 2048 (order: 1, 8192 bytes) Dentry cache hash table entries: 65536 (order: 6, 262144 bytes) Inode-cache hash table entries: 32768 (order: 5, 131072 bytes) Sorting __ex_table... Memory: 424980K/524288K available (4172K kernel code, 208K rwdata, 1304K rodata, 196K init, 149K bss, 99308K reserved, 0K highmem) Kernel virtual memory layout: * 0xfffcf000..0xfffff000 : fixmap * 0xff800000..0xffc00000 : highmem PTEs * 0xff7fe000..0xff800000 : early ioremap * 0xe1000000..0xff7fe000 : vmalloc & ioremap SLUB: HWalign=32, Order=0-3, MinObjects=0, CPUs=1, Nodes=1 NR_IRQS:512 nr_irqs:512 16 ------------[ cut here ]------------ kernel BUG at arch/powerpc/platforms/86xx/pic.c:42! Oops: Exception in kernel mode, sig: 5 [#1] MPC86xx HPCN Modules linked in: CPU: 0 PID: 0 Comm: swapper Not tainted 3.12.0 #2 task: c05903e0 ti: c05b4000 task.ti: c05b4000 NIP: c0567438 LR: c0567430 CTR: c0567400 REGS: c05b5ee0 TRAP: 0700 Not tainted (3.12.0) MSR: 00021032 <ME,IR,DR,RI> CR: 24000042 XER: 20000000 GPR00: c0567430 c05b5f90 c05903e0 00000000 c04e4ff8 c051e588 0000008f 00000002 GPR08: c042789c 00000001 0000006f 00000000 22000048 bebffffd 11a7b4e5 200c8000 GPR16: ffbeffff ffffffff 00000000 00000024 00000000 1fec56f8 1fec59a7 00000000 GPR24: 00000000 1fff97e8 40000000 1ffcc6a0 c0bff080 c05c2490 c05c2628 c0585b60 NIP [c0567438] mpc86xx_init_irq+0x38/0x108 LR [c0567430] mpc86xx_init_irq+0x30/0x108 Call Trace: [c05b5f90] [c0567430] mpc86xx_init_irq+0x30/0x108 (unreliable) [c05b5fb0] [c0562784] init_IRQ+0x24/0x38 [c05b5fc0] [c055fde4] start_kernel+0x1bc/0x2ec [c05b5ff0] [00003444] 0x3444 Instruction dump: 3d00c04f 38800000 38a01002 38c00000 38e00100 39088f8c 38600000 90010024 bfa10014 4bffec35 7c690034 5529d97e <0f090000> 3fa0c04f 4bfff391 38600000 ---[ end trace 31fd0ba7d8756001 ]--- Kernel panic - not syncing: Attempted to kill the idle task! Rebooting in 180 seconds.. Thanks & Regards Ashish Khetan

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Re: Unable to access FPGA device with virtual address returned by ioremap()
by Sri Ram Vemulpali Dec. 26, 2013

Dec. 26, 2013

Hi All, I am working on bringing up the board sbc8641d, which is mostly similar in architecture with mpc8641 having powerpc chip. My board was customized to add FPGA. This FPGA was connected as external device to processor on localbus. I am able to boot the board recognizing all the devices, except external device FPGA. I have mentioned in device tree regarding chip select and parent address in processor address domain of the fpga. I have the following problems. I have problem with ioremap returned address to my device in kernel. ioremap takes physical address and returns virtual address. Using virtual address, if I write and read, there is no result. I am writing to scratch pad of the FPGA chip and reading from it the same string. When I read I do not see any value (written value). Second, when I typed command in bash "free -m" it shows 756MB memory available. I used "mem=" commandline option to tell kernel to use 4GB memory. But after booting the kernel it still shows 756MB. Why is this? Can anyone help me in directing where to look to debug this. Any help would be appreciated. Is there anyway I can debug pagetables to see what is happening at address mapping level. NOTE: this is powerpc architecture. On Wed, Dec 25, 2013 at 3:53 PM, Sri Ram Vemulpali <sri.ram.gmu06(a)gmail.com>wrote: > Hi All, > > I am working on bringing up the board sbc8641d, which is mostly similar in > architecture with mpc8641 having powerpc chip. My board was customized to > add FPGA. This FPGA was connected as external device to processor on > localbus. I am able to boot the board recognizing all the devices, except > external device FPGA. I have mentioned in device tree regarding chip select > and parent address in processor address domain of the fpga. I have the > following problems. > > I have problem with ioremap returned address to my device in kernel. > ioremap takes physical address and returns virtual address. Using virtual > address, if I write and read, there is no result. I am writing to scratch > pad of the FPGA chip and reading from it the same string. When I read I do > not see any value (written value). > > Second, when I typed command in bash "free -m" it shows 756MB memory > available. I used "mem=" commandline option to tell kernel to use 4GB > memory. But after booting the kernel it still shows 756MB. Why is this? > > Can anyone help me in directing where to look to debug this. Any help > would be appreciated. Is there anyway I can debug pagetables to see what is > happening at address mapping level. > > NOTE: this is powerpc architecture. > > -- > Regards, > Sri. > -- Regards, Sri.

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how to find kernel patch applied on existing build kernel
by Vipul Jain Dec. 25, 2013

Dec. 25, 2013

Hi, If I would like to find out if any particular build kernel has a particular patch applied to that kernel how to go about it? Regards, Vipul.

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Re: Spinlocks & schedule_timeout
by SaNtosh kuLkarni Dec. 25, 2013

Dec. 25, 2013

Sent from my Sony Xperia™ smartphone On Dec 25, 2013 4:16 PM, "Pranay Srivastava" <pranjas(a)gmail.com> wrote: > > Hi santosh > > I hope you understand difference between semaphores and spin locks. > Ya I am completely aware of sleeping locks n spin locks > If however you are stuck a situation where you can afford being preempted then you can use sem/mutex. But i think your serialization requires that you use spin locks then best is to have a guarded variable with spin lock and release the lock before you schedule. > I just wanted to verify if it was possible n if yes considering preemption is disabled.. > Even if you set the state preempt count would be increased when you acquire spin lock. so you Cant schedule or go to sleep after spin lock. > Since schedule_timout would make sure the task remains on the run queue and intended to be scheduled back after the specificed jeffies period. It was just out of curiosity anyway .Thanks !!! > Regards > > On Dec 25, 2013 3:36 PM, "SaNtosh kuLkarni" <santosh.yesoptus(a)gmail.com> wrote: >> >> Hi, >> >> I wanted to verify/clarify if using schedule_timeout after acquiring a spinlock is safe?. So basically you have a situation where you are working on a critical code and you acquire a spin lock and you end up using a schedule_timeout after say setting the current task to Interruptible state 'cause you are waiting for some user space code to fill in some buffer from which you want to read. >> So my doubt is simple, is it safe to acquire a spinlock and use schedule_timeout. >> I assume the task is put in the run queue and will "ALWAYS" be scheduled back after the specified delay in schedule_timeout. >> >> -- >> Regards, >> Santosh >> >> _______________________________________________ >> Kernelnewbies mailing list >> Kernelnewbies(a)kernelnewbies.org >> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >>

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回复：Re: Linux-wireless: why use macro to call functions
by zhnzhong521＠sina.com Dec. 25, 2013

Dec. 25, 2013

It's for code reuse. BR.Nianzhong. ----- 原始邮件 ----- 发件人：Valdis.Kletnieks@vt.edu 收件人：Adrian Ratnapala <adrian.ratnapala(a)gmail.com> 抄送人：kernelnewbies <kernelnewbies(a)kernelnewbies.org>, Fred Chou <fred.chou.nd(a)gmail.com> 主题：Re: Linux-wireless: why use macro to call functions 日期：2013年12月25日 00点47分

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RE: Linux-wireless: why use macro to call functions
by Martin Brugnara Dec. 24, 2013

Dec. 24, 2013

Hi, Why here is used a macro instead of an inline func. Thanks, Martin -----Original Message----- From: "Daniel Baluta" <daniel.baluta(a)gmail.com> Sent: ‎23/‎12/‎2013 08.27 To: "Fred Chou" <fred.chou.nd(a)gmail.com> Cc: "kernelnewbies" <kernelnewbies(a)kernelnewbies.org> Subject: Re: Linux-wireless: why use macro to call functions On Mon, Dec 23, 2013 at 8:05 AM, Fred Chou <fred.chou.nd(a)gmail.com> wrote: > Hi, > > I was studying the Linux wireless subsystem code and noticed this code (in > ieee80211_rx_handlers): > > It first defines the macro: > > #define CALL_RXH(rxh) \ > do { \ > res = rxh(rx); \ > if (res != RX_CONTINUE) \ > goto rxh_next; \ > } while (0); > > Then the macro is used to call a series of functions: > > CALL_RXH(ieee80211_rx_h_check_more_data) > CALL_RXH(ieee80211_rx_h_uapsd_and_pspoll) > CALL_RXH(ieee80211_rx_h_sta_process) > CALL_RXH(ieee80211_rx_h_decrypt) > CALL_RXH(ieee80211_rx_h_defragment) > CALL_RXH(ieee80211_rx_h_michael_mic_verify) > > > My question is, why not just call the functions directly like: > > ieee80211_rx_h_check_more_data(rx); > ieee80211_rx_h_uapsd_and_pspoll(rx); > > ... > > Is it just for the sake of outlining the code for easy reading? Appreciate > if anyone can explain. Thanks! Hi, As you can see above the macro does also error checking.I don't necessarily think that the code is easier to read, but it can save you some typing. thanks, Daniel. _______________________________________________ Kernelnewbies mailing list Kernelnewbies(a)kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies

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Linux-wireless: why use macro to call functions
by Fred Chou Dec. 23, 2013

Dec. 23, 2013

Hi, I was studying the Linux wireless subsystem code and noticed this code (in ieee80211_rx_handlers): It first defines the macro: #define CALL_RXH(rxh) \ do { \ res = rxh(rx); \ if (res != RX_CONTINUE) \ goto rxh_next; \ } while (0); Then the macro is used to call a series of functions: CALL_RXH(ieee80211_rx_h_check_more_data) CALL_RXH(ieee80211_rx_h_uapsd_and_pspoll) CALL_RXH(ieee80211_rx_h_sta_process) CALL_RXH(ieee80211_rx_h_decrypt) CALL_RXH(ieee80211_rx_h_defragment) CALL_RXH(ieee80211_rx_h_michael_mic_verify) My question is, why not just call the functions directly like: ieee80211_rx_h_check_more_data(rx); ieee80211_rx_h_uapsd_and_pspoll(rx); ... Is it just for the sake of outlining the code for easy reading? Appreciate if anyone can explain. Thanks! Regards, Fred

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