- kernelnewbies@kernelnewbies.org - Kernelnewbies Mailing Lists

kmalloc - Crashing
by Lloyd Aug. 18, 2021

Aug. 18, 2021

Hi, I am starting to write linux kernel mode code. I am on Ubuntu 20.04. I have written the following code The line DynPage[i]=0; //CRASH causes a crash. Can you please guide on the reason for the crash? Thanks a lot in advance, Lloyd #pragma GCC push_options #pragma GCC optimize("O0") void ClearMem(void) { unsigned int* DynPage=NULL; unsigned int i=0; DynPage=kmalloc(1024*16,GFP_KERNEL); if(DynPage!=NULL) { DynPage[i]=0; //CRASH } kfree(DynPage); DynPage=NULL; return; } #pragma GCC pop_options

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Process after patch has been reviewed and reviewed-by: tag added
by nishad kamdar Aug. 18, 2021

Aug. 18, 2021

Hello, I submitted a patch here: https://patchwork.kernel.org/project/linux-mmc/patch/20210812065730.3986-1-… It has been reviewed and the reviewed-by: tag has been added. But since then it has been a week and there is no activity. I wanted to know what happens after this step and is the patch ready for acceptance ? Should I remind some of the maintainers to look into this patch or is there nothing to be done from my end? Thanks for your time and any suggestions would be appreciated. Thanks and Regards, Nishad

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"Forcibly" disabling a config option (CONFIG_BLOCK)?
by Ian Pilcher Aug. 17, 2021

Aug. 17, 2021

I need to test a kernel build with the block layer (CONFIG_BLOCK) disabled. Starting with a realistic configuration, I haven't found a way to disable it, as it's selected by so many other options. Is there any convenient way to "forcibly" disable an option (along with everything that depends on or selects it)? TIA! -- ======================================================================== In Soviet Russia, Google searches you! ========================================================================

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Problem for testing linux-next
by Sidong Yang Aug. 16, 2021

Aug. 16, 2021

Hi, all. I'm trying to test linux-next. I'm using QEMU for testing. I cloned linux-next repository and checkout to last tag next-20210812. I compiled with simple command below. make menuconfig make & make modules_install & make install and rebooted system. and it failed. It hangs after the message "freeing unused kernel image (init mem) memory" after about 500 seconds, it prints call trace including "x2apic_send_IPI" and it blocked. I want to copy and past it to here. but I don't know how to see the dmesg in last failed session. Is there any wrong configuration for compiling? I would paste it if I could copy the error message. Thanks, Sidong

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kernel / system configuration question regarding "unstable filesystems"
by Colin Williams Aug. 16, 2021

Aug. 16, 2021

Hello, I'm using a SD card to boot my device. The SD card is connected via a USB-C hub due to the device not having any other connectors. This hub and slot will lose power temporarily if plugging in or unplugging power passthrough to the hub. Then on these events the filesystem becomes unmounted and while my system is still running, it becomes unusable. I get input / output errors for example from the terminal. I think what's going on is some portion of the system is loaded into memory. However many critical parts become unavailable. Then I'm curious what options I have at the kernel or system level to ruggedize this so these events don't destroy the system. Before exposing my own ignorance presenting any ideas with my limited knowledge regarding this topic. Is anyone familiar enough to suggest some design approaches or where I might find the best answer regarding a designed solution?

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VFS: Cannot open root device "(null)" or unknown-block(0, 0): error -2
by jim.cromie＠gmail.com Aug. 15, 2021

Aug. 15, 2021

Im trying to configure a minimal kernel, that will work on a virtme / qemu / kvm stack I did make allnoconfig virtme-configkernel --update then I added BTRFS_FS, since thats the host fs. of course it didnt work. then tried DM, needed MD, added both, again didnt help. so I need to stop just guessing. (admittedly, asking is worse ?) heres how it actually goes: 9pnet: Installing 9P2000 support sched_clock: Marking stable (3466602654, 29303733)->(4050551166, -554644779) Btrfs loaded, crc32c=crc32c-generic, zoned=no 9pnet_virtio: no channels available for device /dev/root VFS: Cannot open root device "(null)" or unknown-block(0,0): error -2 Please append a correct "root=" boot option; here are the available partitions: Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) CPU: 0 PID: 1 Comm: swapper Tainted: G W 5.14.0-rc4+ #5 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-4.fc34 04/01/2014 Call Trace: dump_stack+0x1b/0x1d panic+0x95/0x202 mount_block_root+0x204/0x268 mount_root+0x5d/0x62 Heres a working kernel (if overlarge config) It has btrfs, md, which is why I took those guesses above zswap: loaded using pool lzo/zbud Key type ._fscrypt registered Key type .fscrypt registered Key type fscrypt-provisioning registered Btrfs loaded, crc32c=crc32c-generic, zoned=yes Key type encrypted registered PM: Magic number: 1:872:1009 RAS: Correctable Errors collector initialized. md: Skipping autodetection of RAID arrays. (raid=autodetect will force) qemu-system-x86_64: warning: 9p: degraded performance: a reasonable high msize should be chosen on client/guest side (chosen msize is <= 8192). See https://wiki.qemu.org/Documentation/9psetup#msize for details. VFS: Mounted root (9p filesystem) readonly on device 0:20. devtmpfs: mounted Freeing unused decrypted memory: 2036K Anybody see any clues ?

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My effort to learn Linux kernel development
by Amit Kumar Aug. 15, 2021

Aug. 15, 2021

Hi All, I am just here to inform that I am trying to learn Linux kernel development. If someone wants to follow me, so that he may also learn with me. https://freeark1blog.blogspot.com/2021/07/my-aspiration-go-live.html https://freeark1blog.blogspot.com/2021/07/the-minimal-c-program.html https://twitter.com/freeark1 I'll send update on this mail thread. Please, stay tuned. Regards, Amit Kumar

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Linux Kernel build dpkg-buildpackage error
by Adverg Ebashinskii Aug. 15, 2021

Aug. 15, 2021

Hello! I’m trying to build Linux Kernel from upstream and faced some build error. Environment: Ubuntu 20.04 gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0 Linux Kernel 5.8.0-59-generic Steps to build: I follow the instructions specified in this site https://wiki.ubuntu.com/KernelTeam/GitKernelBuild 1 cp /boot/config-$(uname -r) .config 2 make olddefconfig 3 make clean 4 make -j $(getconf _NPROCESSORS_ONLN) deb-pkg LOCALVERSION=-custom After pretty long time of compiling source files I got the following error: make[2]: *** [debian/rules:7: build-arch] Error 2 dpkg-buildpackage: error: debian/rules binary subprocess returned exit status 2 make[1]: *** [scripts/Makefile.package:77: deb-pkg] Error 2 make: *** [Makefile:1559: deb-pkg] Error 2 Is there a way to fix that? -- Regards, Adverg Ebashinskii

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None
by Adverg Ebashinskii Aug. 15, 2021

Aug. 15, 2021

Hello! I’m trying to build Linux Kernel from upstream and faced some build error. Environment: Ubuntu 20.04 gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0 Linux Kernel 5.8.0-59-generic Steps to build: I follow the instructions specified in this site https://wiki.ubuntu.com/KernelTeam/GitKernelBuild 1 cp /boot/config-$(uname -r) .config 2 make olddefconfig 3 make clean 4 make -j $(getconf _NPROCESSORS_ONLN) deb-pkg LOCALVERSION=-custom After pretty long time of compiling source files I got the following error: make[2]: *** [debian/rules:7: build-arch] Error 2 dpkg-buildpackage: error: debian/rules binary subprocess returned exit status 2 make[1]: *** [scripts/Makefile.package:77: deb-pkg] Error 2 make: *** [Makefile:1559: deb-pkg] Error 2 Is there a way to fix that? -- Regards, Adverg Ebashinskii

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Re: USB-Audio: Device or resource busy (strace log)
by Muni Sekhar Aug. 13, 2021

Aug. 13, 2021

On Wed, Aug 11, 2021 at 6:19 PM vishnu <vardhanraj4143(a)gmail.com> wrote: > > can you paste output of > arecord -l (list of capture devices). $ arecord -l **** List of CAPTURE Hardware Devices **** card 0: USB [Plantronics .Audio 628 USB], device 0: USB Audio [USB Audio] Subdevices: 1/1 Subdevice #0: subdevice #0 > Which device you are using and os. > Does this instance is already open by default? like any video playing or something like that? lsof does not catch it. > > Yes you can stop pulse audio and try.. > > On Wed, Aug 11, 2021 at 6:17 PM Jaroslav Kysela <perex(a)perex.cz> wrote: >> >> On 11. 08. 21 14:36, Muni Sekhar wrote: >> > Hi All, >> > >> > $ cat /proc/asound/cards >> > 0 [USB ]: USB-Audio - Plantronics .Audio 628 USB >> > Plantronics Plantronics .Audio 628 USB at >> > usb-0000:00:14.0-2, full speed >> > >> > I am using a Plantronics USB Audio headset. >> > >> > $ arecord --device hw:0,0 --channels 2 --format S16_LE --rate 44100Hz x.wav >> > arecord: main:722: audio open error: Device or resource busy >> > >> > >> > 'arecord' command always fails the first time after system boot in my >> > system. But subsequent execution of the 'arecord' command runs fine. >> > >> > >> > I've attached the strace log for the "audio open error: Device or >> > resource busy" failure. Is there any fix available for this issue? >> >> You may check which other task blocks the PCM device: >> >> lsof /dev/snd/pcmC0D0c It does not output any process. $ lsof /dev/snd/pcmC0D0c 1st run: ---------- $ arecord --device hw:0,0 --channels 2 --format S16_LE --rate 44100Hz x.wav arecord: main:722: audio open error: Device or resource busy 2nd run: ---------- $ arecord --device hw:0,0 --channels 2 --format S16_LE --rate 44100Hz x.wav Recording WAVE 'x.wav' : Signed 16 bit Little Endian, Rate 44100 Hz, Stereo ^CAborted by signal Interrupt... >> >> I guess that it will be pulseaudio (device enumeration). >> >> Jaroslav >> >> -- >> Jaroslav Kysela <perex(a)perex.cz> >> Linux Sound Maintainer; ALSA Project; Red Hat, Inc. -- Thanks, Sekhar

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