April 2019 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

would a Kconfig directive "select CONFIG_x" even work?
by Robert P. J. Day April 12, 2019

April 12, 2019

i could figure this out by RTFM, i suppose, but what the heck ... given that the proper Kbuild directive would be: select x what would happen if someone accidentally wrote: select CONFIG_x would that fail to select Kbuild directive "x", or would the Kbuild system quietly strip the "CONFIG_" prefix because it knew what you really wanted and was trying to be helpful? 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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Memory Configuration for 32-bit, 64-bit and PAE enabled OS
by Pankaj Suryawanshi April 8, 2019

April 8, 2019

I am confuse about memory configuration, i have below questions. 1.if 32-bit os maximum virtual address is 4GB, When i have 4 gb of ram for 32-bit os, What about the virtual memory size ? is it required virtual memory(disk space) or we can directly use physical memory ? 2.In 32-bit os 12 bits are offset because page size=4k i.e 2^12 and 2^20 for page addresses What about 64-bit os, What is offset size ? What is page size ? How it calculated. 3.What is PAE? If enabled how to decide size of PAE, what is maximum and minimum size of extended memory. Regards, Pankaj

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How to calculate page address to PFN in user space.
by Pankaj Suryawanshi April 6, 2019

April 6, 2019

Hello, I have PFN of all processes in user space, how to calculate page address to PFN. eg . page address :bf05febc in kernel space. I have PFN no for user space processes as below. 8a81b 69da0 88cf4 88d06 88d07 9549f 952d0 9734a 87c7d 87ca0 How to calculate/match page address to PFN ? Regards, Pankaj

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How to calculate page address to PFN
by Pankaj Suryawanshi April 5, 2019

April 5, 2019

Hello, I have PFN of all processes in user space, how to calculate page address to PFN. eg . page address :bf05febc in kernel space. I have PFN no for user space processes as below. 8a81b 69da0 88cf4 88d06 88d07 9549f 952d0 9734a 87c7d 87ca0 How to calculate/match page address to PFN ? Regards, Pankaj

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how to collect information regarding function calls in run time?
by Pedro Terra Delboni April 3, 2019

April 3, 2019

Hello! I have a question about profiling, please, let me know if this is not the right mailing list to post these kind of questions. Is there a way for me to record how many times each specific direct call to a function happened? I've seen ways of profiling the kernel that calculate how much time the system spent in each function, but having a bit more information related to calls would be really good. I would like to know, for every function call that happens in run time, who called it (it's for a project in my University). I've also seen (I may be mistaken here) that by compiling the kernel with perf, each function will start with a stub call which can be used for profiling purposes. I was thinking in using this stub to plug a function to dump (somewhere) the return address before it's own (so I can collect the info about where the call came from). I wonder if changing every stub calls in all functions to dump its return address wouldn't create too much of a latency impact to the point of skewing the control flow of the execution, or even making it nonviable. Thanks in advance, any help would be great! If this is not the right place to post this question, I would appreciate if anyone could point me to the right place. Thanks Pedro

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Unexpected scheduling with mutexes
by Martin Christian April 3, 2019

April 3, 2019

Hi, I've written a linux kernel module for an USB device. The USB driver provides 2 read-only character devices, which can be opened only exclusively by one process: - `/dev/cdev_a` - `/dev/cdev_b` The USB device can only handle one request at a time. The test setup is a follows: - Processes A reads data from 1st device: `dd if=/dev/cdev_a of=/tmp/a bs=X` - Processes B reads data from 2nd device: `dd if=/dev/cdev_b of=/tmp/b bs=X` - Process A and B run in parallel - After 10 seconds both processes are killed and size of both output files is compared. For certain values of `X` there is a significant difference in size between the two files, which I don't expect. A read call to the driver does the following: 1. `mutex_lock_interruptible(iolock)` 2. `usb_bulk_msg(dev, pipe, buf, X, timeout)` 3. `mutex_unlock(iolock)` 4. `copy_to_user(buf)` What I would expect is the following: 1. Proc A: `mutex_lock_interruptible(iolock)` 2. Proc A: `usb_bulk_msg(dev, pipe, buf, X, timeout)` 3. Scheduling: A -> B 4. Proc B: `mutex_lock_interruptible(iolock)` -> blocks 5. Scheduling: B -> A 6. Proc A: `mutex_unlock(iolock)` 7. Proc A: `copy_to_user(buf)` 8. Proc A: `mutex_lock_interruptible(iolock)` -> blocks 9. Scheduling: A -> B 10. Proc B: `usb_bulk_msg(dev, pipe, buf, X, timeout)` But what I see with ftrace is that in step 8, process A still continues. And it seems that for certain values of X the time inside the critical region is a multiple of the time slice, so that process B always gets the time slice when the critical region is blocked. What would be a best practise solution for this? I was thinking of calling `schedule()` each time after copying to user space or playing with nice values or using wait_queues? -- Dipl.-Inf. Martin Christian Senior Berater Entwicklung Hardware secunet Security Networks AG Tel.: +49 201 5454-3612, Fax +49 201 5454-1323 E-Mail: martin.christian(a)secunet.com Ammonstraße 74, 01067 Dresden www.secunet.com

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Questions about my idea (for gsoc)
by Andrea Laisa April 1, 2019

April 1, 2019

Hi! I'm a student that want to do a google summer of code with you during this summer. My idea is to write a Linux driver for a proprietary network protocol used by the outdoor Gemtek antennas(which are essentially a LTE modem) to communicate over ethernet+LLC to the indoor Gemtek Access Points. My goal is to allow anyone to use any Linux-based router (like a Turris Omnia/openwrt) instead of a Gemtek Access Point. I think it's a great idea but I have some questions. -In which area my idea is located? networking? -Should the idea implemented as Linux driver or as userspace program?

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Re: Questions about my idea (for gsoc)
by Andrea Laisa April 1, 2019

April 1, 2019

I'm not sure what project i'm looking to apply, maybe a netdev driver? Or two network protocol driver with a userspace daemon/utilities to control the antenna? Or just a userspace daemon/utilities. I don't have a clear idea where I should write the code that controls the antenna. Il 01/04/19 20:28, Andrea Laisa ha scritto: > Il 01/04/19 19:16, Greg KH ha scritto: >> Who is "you" here? What project specifically are you looking to apply >> to that asked you to post on the kernelnewbies list? > > As "you" I mean all linux kernel hacker. > > > Il 01/04/19 19:16, Greg KH ha scritto: >> - do you have documentation for how this protocol works? >> - do you have access to hardware where you could test these kernel >> changes? > > Yes, I have access to my home antenna (and access point), but I don't > have any tyoe of official documentation because it doesn't exist or I > doesnt't found it, > > I have sniffed my network traffic between the access point and the > antenna and I discovered(with wireshark) that they use a custom > protocol over LCC (dsap 0x40 and 0x10) to setup the connection to my > ISP via LTE. After the setup the AP routes the LAN network traffic to > the antenna as expected over a 802.1q-tagged IP packet(with VLAN > ID=1121). > > Although I don't have access to the protocol specifications, I'm going > to reverse engineering the protocol! >

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da9063 - Reboot issue : koops rcu_note_context_switch
by Köry Maincent April 1, 2019

April 1, 2019

Hello, I got a kernel warning on the reboot of my embedded board, and sometimes I got stuck in the reboot. I work on the IMX6Q with a PMIC da9063 and the last kernel release. It happens in the da9063_wdt_restart function at the regmap_write call in the CONTROL_F register. (drivers/watchdog/da9063_wdt.c) If I access to other register in that function, I don't have this issue. I don't see the link between the rcu as noted in the koops and the write in a specific register of the pmic. Could you help me to go further in the debug? [ 32.850293] ------------[ cut here ]------------ [ 32.854929] WARNING: CPU: 0 PID: 724 at kernel/rcu/tree_plugin.h:337 rcu_note_context_switch+0xac/0x554 [ 32.864322] Modules linked in: [ 32.867386] CPU: 0 PID: 724 Comm: reboot Not tainted 5.0.4-yocto-standard+ #49 [ 32.874609] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree) [ 32.881155] [<80111164>] (unwind_backtrace) from [<8010c81c>] (show_stack+0x10/0x14) [ 32.888911] [<8010c81c>] (show_stack) from [<808bde64>] (dump_stack+0x88/0x9c) [ 32.896147] [<808bde64>] (dump_stack) from [<8012077c>] (__warn+0xdc/0xf4) [ 32.903031] [<8012077c>] (__warn) from [<801208ac>] (warn_slowpath_null+0x40/0x48) [ 32.910607] [<801208ac>] (warn_slowpath_null) from [<8017596c>] (rcu_note_context_switch+0xac/0x554) [ 32.919751] [<8017596c>] (rcu_note_context_switch) from [<808d78f8>] (__schedule+0x70/0x584) [ 32.928196] [<808d78f8>] (__schedule) from [<808d7e60>] (schedule+0x54/0xb0) [ 32.935256] [<808d7e60>] (schedule) from [<808dbc5c>] (schedule_hrtimeout_range_clock+0xd8/0x15c) [ 32.944137] [<808dbc5c>] (schedule_hrtimeout_range_clock) from [<808dbcf8>] (schedule_hrtimeout_range+0x18/0x20) [ 32.954319] [<808dbcf8>] (schedule_hrtimeout_range) from [<808db630>] (usleep_range+0x6c/0x90) [ 32.962941] [<808db630>] (usleep_range) from [<80681ac4>] (i2c_imx_start+0xa0/0x13c) [ 32.970692] [<80681ac4>] (i2c_imx_start) from [<80682874>] (i2c_imx_xfer+0x68/0xe94) [ 32.978447] [<80682874>] (i2c_imx_xfer) from [<8067c4c4>] (__i2c_transfer+0x168/0x2cc) [ 32.986372] [<8067c4c4>] (__i2c_transfer) from [<8067c68c>] (i2c_transfer+0x64/0xe4) [ 32.994128] [<8067c68c>] (i2c_transfer) from [<804dee9c>] (regmap_i2c_read+0x58/0x88) [ 33.001968] [<804dee9c>] (regmap_i2c_read) from [<804daee4>] (_regmap_raw_read+0xac/0x11c) [ 33.010239] [<804daee4>] (_regmap_raw_read) from [<804daf8c>] (_regmap_bus_read+0x38/0x60) [ 33.018511] [<804daf8c>] (_regmap_bus_read) from [<804da0a8>] (_regmap_read+0x60/0xb8) [ 33.026436] [<804da0a8>] (_regmap_read) from [<804da508>] (_regmap_update_bits+0xb0/0xec) [ 33.034620] [<804da508>] (_regmap_update_bits) from [<804da5e0>] (_regmap_select_page+0x9c/0xf8) [ 33.043412] [<804da5e0>] (_regmap_select_page) from [<804dab18>] (_regmap_raw_write_impl+0x4dc/0x69c) [ 33.052637] [<804dab18>] (_regmap_raw_write_impl) from [<804db5ec>] (regmap_write+0x3c/0x5c) [ 33.061087] [<804db5ec>] (regmap_write) from [<806be9ec>] (da9063_wdt_restart+0x54/0xa0) [ 33.069185] [<806be9ec>] (da9063_wdt_restart) from [<806bd288>] (watchdog_restart_notifier+0x18/0x2c) [ 33.078416] [<806bd288>] (watchdog_restart_notifier) from [<8013f148>] (notifier_call_chain+0x48/0x84) [ 33.087731] [<8013f148>] (notifier_call_chain) from [<8013f3d0>] (atomic_notifier_call_chain+0x34/0x48) [ 33.097138] [<8013f3d0>] (atomic_notifier_call_chain) from [<8010b12c>] (machine_restart+0x78/0x7c) [ 33.106194] [<8010b12c>] (machine_restart) from [<80140aac>] (sys_reboot+0xd8/0x1d0) [ 33.113945] [<80140aac>] (sys_reboot) from [<80101000>] (ret_fast_syscall+0x0/0x54) [ 33.121604] Exception stack(0xed1e1fa8 to 0xed1e1ff0) [ 33.126663] 1fa0: 00012230 7e895db4 fee1dead 28121969 01234567 00000000 [ 33.134847] 1fc0: 00012230 7e895db4 00000003 00000058 000225f8 00000000 00000000 00000000 [ 33.143027] 1fe0: 76f26ea0 7e895c14 00010fd8 76f26ec0 [ 33.148080] ---[ end trace 1e06dce5f82e2a7a ]--- -- Regards Kory

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