June 2017 - kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

where is __percpu_seg initialized?
by 落痕 March 28, 2018

March 28, 2018

Hi all: I knew the kernel implement the per-cpu variable via __percpu_seg. For example on x86 architecture, it's defined as: #ifdef CONFIG_X86_64 #define __percpu_seg gs #define __percpu_mov_op movq #else #define __percpu_seg fs #define __percpu_mov_op movl #endif But I'm curious where __percpu_seg is initialized?? I fail to find the relative code. Thanks.

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How to handle Hotplug with UIO userspace driver
by Mandeep Sandhu Sept. 28, 2017

Sept. 28, 2017

Hi All, We're working on a custom PCIe based hardware, which can be hotplugged into the system. We're using the UIO approach of having a minimal kernel driver which basically handles the interrupt and provides a mmap of the device memory to userspace and userspace driver which mmap's the provided memory and manages the device. We're using systemd and udev rules to spawn off a user process whenever the hardware is plugged into the system. Now my question is, how can we gracefully inform the userspace process if someone pulls out the hardware (sitting on a PCI slot). Even with full hotplug support, there can always be a case of "surprise removal", where someone yanks the board without going through the whole "attention button" routine. While the kernel driver has no problem with hot-removal, I see that if I "unregister" our UIO driver in response to the removal, then the mapping for the hardware's physical memory would become "invalid" (done by UIO on unregsiter). This could possibly cause the user-space process to crash due to illegal memory access. Is there a "standard" way to handle this scenario, i.e for hotpluggable hardware using UIO? Basically, we'd want to "unregister" the UIO device only after the userspace process is informed of the removal so that it could unmap/close the device and exit gracefully. We could try doing it using some systemd trick, where we put a dependency on one of the UIO created files (/dev/uioX), so that when the file is destroyed, systemd could kill/shutdown the process. Although, there's no guarantee that the userspace process won't try to access the mmaped space during that interval, so this isn't a reliable solution either. Any hints, thoughts? Thanks., -mandeep

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building af_packet as a kernel module
by Kevin Wilson July 3, 2017

July 3, 2017

Hello, I have tried to set CONFIG_PACKET=m in kernel 4.11 and rebuilt the kernel and rebooted. I am using Ubuntu 16.04. After reboot, the af_packet.ko kernel module is loaded: lsmod shows: af_packet 45056 2 But I cannot remove it: rmmod af_packet rmmod: ERROR: Module af_packet is in use I want to be able to rmmod it, for adding debug printing, etc. How can I find which applications uses it ? (So I will be able to stop them, rmmod af_packet, and then insmod it again)? Regards, Kevin

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Qemu+busybox for kernel development
by Alexander Kapshuk July 2, 2017

July 2, 2017

I am trying to setup a build environment where I can run the kernel and see how the changes I have made to the kernel source work. My understanding, based on googling, is that it is common practice in the kernel community to use a virtualised environment for that purpose. What I have done so far is create a ramfs that is built into the kernel, as described here [1] and here [2]. [1] https://landley.net/writing/rootfs-howto.html [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/Do… a). I have generated a minimal initramfs_list file: scripts/gen_initramfs_list.sh -d >usr/initramfs_list Which looks like this: # This is a very simple, default initramfs dir /dev 0755 0 0 nod /dev/console 0600 0 0 c 5 1 dir /root 0700 0 0 # file /kinit usr/kinit/kinit 0755 0 0 # slink /init kinit 0755 0 0 slink /bin/sh busybox 777 0 0 file /init /bin/busybox 755 0 0 b). Set CONFIG_INITRAMFS_SOURCE: CONFIG_INITRAMFS_SOURCE="/home/sasha/linux/usr/initramfs_list" c). And had the kernel generate the initramfs image: make ... GEN usr/initramfs_data.cpio.gz CHK include/generated/compile.h AS usr/initramfs_data.o LD usr/built-in.o ... When I run the kernel in qemu I get an error message which complains about /etc/init.d/rcS missing. The posts online seem to suggest that this has got to do with the busybox configuration. So far, I have not been able to get my head around this problem. Any points or suggestions would be much appreciated. Alexander Kapshuk.

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Keeping track of called syscalls in real-time
by Ben Mezger June 29, 2017

June 29, 2017

Can the kernel keep track of all the system calls that were called by an application/module in real-time? I know I can statically use strace, or even gdb, but I am looking for a solution in real time when the application/module is already running and the user has no control over it. I am not sure if a system call needs to go through a sort of wrapper to get it from the syscall table, which I'm then assuming I can get such info from there, but I am not sure. I am looking for hints/options to archive this. Many thanks -- - seds ~> https://seds.nl

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Kernel schedules kernel tasks on isolated cpus, SCHED_FIFO prevents kernel tasks from running
by Andrei Hurynovich June 28, 2017

June 28, 2017

Hi. We are trying to build realtime(-ish) system based on rhel6(kernel 2.6.32-642.1.1.el6.x86_64). We used isolcpus to remove some cpus from process scheduling(isolcpus=2-19 nohz_full=2-19 rcu_nocbs=2-19). We spin off a program thread that set's its cpu affinity to one of those isolated cpus, sets its scheduling chass to SCHED_FIFO, spins in a loop and never sched_yield()-s to the kernel. We set sysctl kernel.sched_rt_runtime_us = -1 so realtime threads are NEVER interrupted. We are observing that the program thread is indeed realtime and is never interrupted. After some time working like this, the system becomes irresponsive - ssh connections start failing with timeout, existing connections hang when trying to read/write to physical disks(reading procfs or writing to tmpfs is unaffected). *** According to /proc/sched_debug, it seems that kernel still schedules some SCHED_OTHER(e.g. non-realtime) kernel tasks to isolated cpus - for example cpu 18 get tasks events/18 and kblockd/18 that are stuck in runnable(but not running state), so those kernel processes never got a single time slice because our realtime process hogs 100% of cpu. And kernel/18 and kblockd/18 never migrate to other cpus because these tasks are pinned to cpu 18. *** Check please these /proc/sched_debug snapshots, you can see that events/18 and kblockd/18 sum-exec counters are not increasing: https://gist.github.com/altmind/5cf4aad87a4a082441c1ca9378a06154 The question is: Is it possible to never schedule kernel tasks on selected cpus? -- Thanks, Andrei Hurynovich

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Error in freeing memory with zone reclaimable always returning true.
by Ivid Suvarna June 26, 2017

June 26, 2017

Hi, I have below code which tries to free memory, do { free=shrink_all_memory; }while(free>0); But kernel gets into infinite loop because shrink_all_memory always returns 1. When I added some debug statements to `mm/vmscan.c` and found that it is because zone_reclaimable() is always true in shrink_zones() if (global_reclaim(sc) && !reclaimable && zone_reclaimable(zone)) reclaimable = true; This issue gets solved by removing the above lines. I am using linux-kernel 4.4 and imx board. Similar Issue is seen here[1]. And it is solved through a patch removing the offending lines. But it does not explain why the zone reclaimable goes into infinite loop and what causes it? And I ran the C program from [1] which is below. And instead of OOM it went on to infinite loop. #include <stdlib.h> #include <string.h> int main(void) { for (;;) { void *p = malloc(1024 * 1024); memset(p, 0, 1024 * 1024); } } Also can this issue be related to memcg as in here " https://lwn.net/Articles/508923/" because I see the code flow in my case enters: if(nr_soft_reclaimed) reclaimable=true; I dont understand memcg correctly. But in my case CONFIG_MEMCG is not set. After some more debugging, I found a userspace process in sleeping state and has three threads. This process is in pause state through system_pause() and is accessing shared memory(`/dev/shm`) which is created with 100m size. This shared memory has some files. Also this process has some anonymous private and shared mappings when I saw the output of `pmap -d PID` and there is no swap space in the system. I found that this hang situation was not present after I remove that userspace process. But how can that be a solution since kernel should be able to handle any exception. "I found no issues at all if I removed this userspace process". So my doubts are: 1. How can this sleeping process in pause state cause issue in zone reclaimable returning true always. 2. How are the pages reclaimed from sleeping process which is using shared memory in linux? 3. I tried to unmount /dev/shm but was not possible since process was using it. Can we release shared memory by any way? I tried `munmap` but no use. Any info would be helpful. [1]: https://groups.google.com/forum/#!topic/fa.linux.kernel/kWwlQzj8mhc Regards, Ivid

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ks7010 cfg80211 re-write
by Tobin C. Harding June 26, 2017

June 26, 2017

May I please ask two questions relating to the correct kernel development protocol to follow for the cfg80211 re-write. Current state: Functional WEXT driver in drivers/staging. Interim state: Partial cfg80211 implementation. Target state: Functional cfg80211 driver in drivers/staging. Future state: Functional cfg80211 driver out of staging. Question 1: Is it correct kernel development protocol to do the interim state in public? - If NO -> end of email. - If YES; Question 2: What is the correct directory structure to have in the interim? 1. Remove WEXT code entirely, substitute in progress cfg80211 code. 2. Move WEXT code to sub directory and remove from build process. 3. Add cfg80211 drive as a new, separate driver, enable kernel configuration for WEXT and cfg80211 as separate drivers. 4. Add cfg80211 code as sub directory keeping functioning WEXT driver in place. 5. Other I don't see how option 3 or 4 are possible and/or sensible. thanks, Tobin.

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struct inode initialization
by vish chopra June 25, 2017

June 25, 2017

Hi, i'm working on character driver.Unable to find when inode structure is create and when inode->i_cdev is assigned. Unable to find relation between inode and cdev. Regards, Vishal Chopra +91-7837583269

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Re: Kernelnewbies Digest, Vol 79, Issue 18
by wiktoria.lewicka June 21, 2017

June 21, 2017

Thank you all, I make some changes in my code, but its still not work. When my module is loading and loading I have a problems with connection with Internet- is it a matter of configuration? My changes: #include <linux/kernel.h> #include <linux/module.h> #include <linux/init.h> #include <linux/netdevice.h> #include <linux/string.h> #define DEV_NAME "my_dev\n" struct net_device my_netdev; int init_mdev(struct net_device *dev); struct net_device_ops nops = { .ndo_init = init_mdev, /*.ndo_uninit = unin_mdev,*/ }; static int __init init_dev(void) { /*my_netdev.netdev_ops = &nops;*/ int result; if(!(netdev_boot_setup_check(&my_netdev))){ printk(KERN_ERR "NETDEV: setup error"); return 0; } strcpy(my_netdev.name, DEV_NAME); if((result = register_netdev(&my_netdev))) printk(KERN_ERR "NETDEV: Error registering device"); printk("NETDEV: Device registered successfully"); return 0; } static void __exit remove_dev(void) { unregister_netdev(&my_netdev); } int init_mdev(struct net_device *dev) { printk("INIT"); return 0; } module_init(init_dev); module_exit(remove_dev); W dniu 2017-06-20 18:00:02 użytkownik <kernelnewbies-request(a)kernelnewbies.org> napisał: > Send Kernelnewbies mailing list submissions to > kernelnewbies(a)kernelnewbies.org > > To subscribe or unsubscribe via the World Wide Web, visit > https://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. My network device don't work (wiktoria.lewicka) > 2. Re: My network device don't work (Stan Drozd) > 3. Re: My network device don't work (Greg KH) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Tue, 20 Jun 2017 14:32:31 +0200 > From: "wiktoria.lewicka" <wiktoria.lewicka(a)vp.pl> > Subject: My network device don't work > To: "kernelnewbies(a)kernelnewbies.org" > <kernelnewbies(a)kernelnewbies.org> > Message-ID: > <186270325-26e3212af6540c227a34d3cd3b5e0c56(a)pmq3v.m5r2.onet> > Content-Type: text/plain; charset="utf-8" > > Hello. > I write simple network device, but its don't work. Module is loading, loading, loading... > Code: > > #include <linux/kernel.h> > #include <linux/module.h> > #include <linux/init.h> > #include <linux/netdevice.h> > #include <linux/string.h> > #define DEV_NAME "chwdp" > > struct net_device my_netdev; > > int init_my_net_dev(struct net_device *dev); > > struct net_device_ops nops = { > .ndo_init = init_my_net_dev, > //.ndo_uninit = uninit_my_net_dev, > }; > > static int __init init_dev(void) > { > //my_netdev.netdev_ops = &nops; > int result; > if((netdev_boot_setup_check(&my_netdev))){ > printk(KERN_ERR "NETDEV: setup error"); > return 0; > } > strncpy(my_netdev.name, DEV_NAME, 5); > if((result = register_netdev(&my_netdev))) > printk(KERN_ERR "NETDEV: Error registering device"); > printk("NETDEV: Device registered successfully"); > return 0; > } > > static void __exit remove_dev(void) > { > unregister_netdev(&my_netdev); > } > int init_my_net_dev(struct net_device *dev) > { > printk("INIT"); > return 0; > } > module_init(init_dev); > module_exit(remove_dev); > > > > > ------------------------------ > > Message: 2 > Date: Tue, 20 Jun 2017 15:31:29 +0200 > From: Stan Drozd <drozdziak1(a)gmail.com> > Subject: Re: My network device don't work > To: "wiktoria.lewicka" <wiktoria.lewicka(a)vp.pl> > Cc: kernelnewbies(a)kernelnewbies.org > Message-ID: <20170620133128.GB1233(a)gmail.com> > Content-Type: text/plain; charset=us-ascii > > On Tue, Jun 20, 2017 at 02:32:31PM +0200, wiktoria.lewicka wrote: > > Hello. > > I write simple network device, but its don't work. Module is loading, loading, loading... > > Code: > > [...] > Hello, > "strncpy(my_netdev.name, DEV_NAME, 5)" only copies the 5 chars in "chwdp" without the null byte. You could bump it to 6 > or maybe change 5 to IFNAMSIZ (the net_device.name's size) and then change the last byte to '\0' manually > > > > ------------------------------ > > Message: 3 > Date: Tue, 20 Jun 2017 22:12:34 +0800 > From: Greg KH <greg(a)kroah.com> > Subject: Re: My network device don't work > To: "wiktoria.lewicka" <wiktoria.lewicka(a)vp.pl> > Cc: "kernelnewbies(a)kernelnewbies.org" > <kernelnewbies(a)kernelnewbies.org> > Message-ID: <20170620141234.GA2599(a)kroah.com> > Content-Type: text/plain; charset=us-ascii > > On Tue, Jun 20, 2017 at 02:32:31PM +0200, wiktoria.lewicka wrote: > > Hello. > > I write simple network device, but its don't work. Module is loading, loading, loading... > > Code: > > > > #include <linux/kernel.h> > > #include <linux/module.h> > > #include <linux/init.h> > > #include <linux/netdevice.h> > > #include <linux/string.h> > > #define DEV_NAME "chwdp" > > > > struct net_device my_netdev; > > > > int init_my_net_dev(struct net_device *dev); > > > > struct net_device_ops nops = { > > .ndo_init = init_my_net_dev, > > //.ndo_uninit = uninit_my_net_dev, > > }; > > > > static int __init init_dev(void) > > { > > //my_netdev.netdev_ops = &nops; > > int result; > > if((netdev_boot_setup_check(&my_netdev))){ > > printk(KERN_ERR "NETDEV: setup error"); > > return 0; > > Why are you returning success if there was an error? > > And always try to use proper kernel coding style when writing kernel > code if you expect/want someone else to read it :) > > thanks, > > greg k-h > > > > ------------------------------ > > _______________________________________________ > Kernelnewbies mailing list > Kernelnewbies(a)kernelnewbies.org > https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > > End of Kernelnewbies Digest, Vol 79, Issue 18 > ********************************************* >

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