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

How to make /dev/ttyACM0 (and friends) exclusive?
by Jeffrey Walton Oct. 11, 2020

Oct. 11, 2020

Hi Everyone, I'm trying to trackdown a problem using my dialup modem. I have a program that opens the modem and watches caller id's. It flashes the hook when a telemarketer calls. It works well until... When another program opens the modem then my program starts reading intermittent responses intended for the other program. I cannot seem to open the device in exclusive mode. The current open is (I also tried with O_EXCL): int modem = open(device_path, O_RDWR | O_NOCTTY | O_SYNC); I'm not sure if it because udev configures the device incorrectly or the kernel driver is configured incorrectly. Or maybe it is impossible to do. Does anyone know how I can make the device exclusive? Thanks in advance.

6 12

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

4 6

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

2 3

maintainer for this update?
by Dave Stevens March 29, 2019

March 29, 2019

In the article below about kernel updates is a reference to a driver for a Plantower PMS7003 particulate matter sensor. I'm using this series in air pollution monitoring and its usual interface to the computer is over a serial line. I consequently am very curious about how and why it would need a specific kernel module. Can anyone refer me to more information about the originator of this patch? I'd rather ask directly but don't know how to go about it. TIA Dave https://lwn.net/Articles/782511/

3 2

Where is PageHead defined in v5.0?
by Tobin C. Harding March 28, 2019

March 28, 2019

Hi, I cannot locate the definition of PageHead? It seems to have disappeared after v4.0? I can see it defined as a function here: https://elixir.bootlin.com/linux/v4.0/source/include/linux/page-flags.h#L401 But on the mainline (v5.1-rc2) I get: $ git grep ' PageHead' include/linux/page-flags.h:int PageHeadHuge(struct page *page); include/linux/page-flags.h: return PageHead(page); include/linux/page-flags.h: return PageHead(page) && test_bit(PG_double_map, &page[1].flags); mm/hugetlb.c: return PageHead(page) && PagePrivate(&page[1]); mm/hugetlb.c: * PageHeadHuge() only returns true for hugetlbfs head page, but not for mm/hugetlb.c:int PageHeadHuge(struct page *page_head) Clearly it is defined _somewhere_. Anyone any idea what brain dysfunction I am having right now? thanks, Tobin.

4 7

Overwriting copy functionality in filesystem
by Bharath Vedartham March 28, 2019

March 28, 2019

Hey everyone, I was wondering how we can overwrite the copy functionality while writing our own filesystem in linux. VFS does not offer any sort of API for copy. I think it calls create and write when we execute the copy the file/dir. I am interested in overwriting the way copy happens in my filesystem(which I am writing for fun :p). Any ideas? Thanks

4 8

Sparse errors
by Bharath Vedartham March 28, 2019

March 28, 2019

Hey all, When I run sparse, I get sparse errors. Sparse says "too many errors". For example when I run: make C=2 fs/ext4/ This is the error messages I get for one of the files. CHECK fs/ext4/ioctl.c ./arch/x86/include/asm/nospec-branch.h:146:38: warning: Unknown escape '@' ./include/linux/compiler.h:190:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/compiler.h:208:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/compiler.h:214:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/barrier.h:36:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/kasan-checks.h:9:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/kasan-checks.h:11:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/compiler.h:271:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/compiler.h:302:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:66:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:89:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:104:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:126:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:132:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:137:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:162:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:177:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:191:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:212:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:224:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:239:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:258:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:279:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:291:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:311:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:316:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:322:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:354:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:368:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:382:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:404:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:445:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/bitops.h:487:8: error: attribute '__gnu_inline__': unknown attribute ./include/asm-generic/bitops/sched.h:13:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/arch_hweight.h:17:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/arch_hweight.h:28:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/arch_hweight.h:33:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/asm/arch_hweight.h:45:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/uapi/asm/swab.h:8:8: error: attribute '__gnu_inline__': unknown attribute ./arch/x86/include/uapi/asm/swab.h:15:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/swab.h:47:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/swab.h:56:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/swab.h:65:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/swab.h:78:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/swab.h:87:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/swab.h:161:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/swab.h:174:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/swab.h:187:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/swab.h:202:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/swab.h:217:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/swab.h:230:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/swab.h:242:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/swab.h:255:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/swab.h:270:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/swab.h:285:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/byteorder/little_endian.h:44:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/byteorder/little_endian.h:48:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/byteorder/little_endian.h:52:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/byteorder/little_endian.h:56:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/byteorder/little_endian.h:60:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/byteorder/little_endian.h:64:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/byteorder/little_endian.h:68:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/byteorder/little_endian.h:72:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/byteorder/little_endian.h:76:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/byteorder/little_endian.h:80:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/byteorder/little_endian.h:84:8: error: attribute '__gnu_inline__': unknown attribute ./include/uapi/linux/byteorder/little_endian.h:88:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/byteorder/generic.h:144:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/byteorder/generic.h:149:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/byteorder/generic.h:154:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/byteorder/generic.h:160:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/byteorder/generic.h:168:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/byteorder/generic.h:176:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/byteorder/generic.h:181:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/byteorder/generic.h:186:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/byteorder/generic.h:191:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/byteorder/generic.h:199:8: error: attribute '__gnu_inline__': unknown attribute ./include/asm-generic/bitops/le.h:12:8: error: attribute '__gnu_inline__': unknown attribute ./include/asm-generic/bitops/le.h:18:8: error: attribute '__gnu_inline__': unknown attribute ./include/asm-generic/bitops/le.h:24:8: error: attribute '__gnu_inline__': unknown attribute ./include/asm-generic/bitops/le.h:53:8: error: attribute '__gnu_inline__': unknown attribute ./include/asm-generic/bitops/le.h:58:8: error: attribute '__gnu_inline__': unknown attribute ./include/asm-generic/bitops/le.h:63:8: error: attribute '__gnu_inline__': unknown attribute ./include/asm-generic/bitops/le.h:68:8: error: attribute '__gnu_inline__': unknown attribute ./include/asm-generic/bitops/le.h:73:8: error: attribute '__gnu_inline__': unknown attribute ./include/asm-generic/bitops/le.h:78:8: error: attribute '__gnu_inline__': unknown attribute ./include/asm-generic/bitops/le.h:83:8: error: attribute '__gnu_inline__': unknown attribute ./include/asm-generic/bitops/le.h:88:8: error: attribute '__gnu_inline__': unknown attribute ./include/asm-generic/bitops/le.h:93:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/bitops.h:43:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/bitops.h:51:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/bitops.h:61:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/bitops.h:71:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/bitops.h:81:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/bitops.h:91:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/bitops.h:101:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/bitops.h:111:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/bitops.h:121:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/bitops.h:131:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/bitops.h:143:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/bitops.h:154:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/bitops.h:160:8: error: attribute '__gnu_inline__': unknown attribute ./include/linux/bitops.h:167:8: error: too many errors I am using gcc 5.4. I am unable to debug this issue and am not finding much help on the internet. Please do ask if more info is required. Thank you

3 5

tty: uart: loopback test
by Subhashini Rao Beerisetty March 27, 2019

March 27, 2019

Hi All, I’m looking for an userspace ‘C’ test code to transfer a file on UART Tx line and receive the file on UART Rx line to test loopback supported serial port. Can anybody give example of such application? Thanks

2 1

Roadmap to Linux development -- Kernel and Utilities
by Milad Kahsari March 26, 2019

March 26, 2019

Hi folks, I am looking for a new and updated roadmap for Linux Kernel/Patch development from scratch. for example, it teaches what knowledge we need and how should we contribute to the project. Is there any roadmap as such for taking?

4 3

problem about subscribe linux-kernel
by kmaillists March 24, 2019

March 24, 2019

hi guys! i want to subscribe linux-kernel from majordomo@vger.kernel.org,i tried to use this account and a hotmail account to do that. This account recevied nothing and the hotmial account received the answer: Hello [40.92.255.58], for your MAIL FROM address <nickzjm(a)hotmail.com> policy analysis reported: Your address is not liked source for email i had send the email with text model,not html model.Anybody know what's the problem? thanks for your time!

3 2