August 2020 - kernelnewbies@kernelnewbies.org

How is the value of KernelStack in /proc/meminfo computed ?
by William Tambe Aug. 7, 2020

Aug. 7, 2020

How is the value of KernelStack in /proc/meminfo computed ? Any pointers in the code source would be much appreciated.

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[PATCH 0/8] dyndbg: WIP diet plan
by Jim Cromie Aug. 6, 2020

Aug. 6, 2020

dynamic-debug metadata is bloated; the __dyndbg linker section is effectively an array of struct _ddebugs, its 1st 3 members are highly repetetive, with 90%, 84%, 45% repeats. Total reported usage ~150kb for ~2600 callsites on my laptop config. This patchset is one diet plan. it all holds together nicely until the "cache" commit, when it blows up starting init (or right after freeing unused kernel image, which Im hoping to do...). The following commit tweaks locking in an attempt to recover, but fails. [ 0.737936] Freeing unused kernel image (initmem) memory: 1196K [ 0.740173] Write protecting the kernel read-only data: 22528k [ 0.743555] Freeing unused kernel image (text/rodata gap) memory: 2040K [ 0.744984] Freeing unused kernel image (rodata/data gap) memory: 256K [ 0.757777] Run /bin/sh as init process q[ 1.029548] Kernel panic - not syncing: Requested init /bin/sh failed (error -14). [ 1.034582] CPU: 0 PID: 1 Comm: sh Not tainted 5.8.0-00026-g9a06159192d6 #14 [ 1.036068] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-2.fc32 04/01/2014 [ 1.037885] Call Trace: [ 1.038444] dump_stack+0x5e/0x7a [ 1.039172] ? memcpy_orig+0x100/0x10f [ 1.039917] panic+0xf6/0x2b7 [ 1.040573] ? rest_init+0xa0/0xa0 [ 1.041314] kernel_init+0xaa/0x100 [ 1.041956] ret_from_fork+0x22/0x30 [ 1.042668] Kernel Offset: disabled [ 1.043216] ---[ end Kernel panic - not syncing: Requested init /bin/sh failed (error -14). ]--- QEMU 4.2.1 monitor - type 'help' for more information (qemu) q Im sending to kernelnewbies 1st, to see if theres any low-speed test-crashes I can get post-mortems of, before I take it to the races. Id appreciate any reviews, tests, or opinions you all might offer (in that order). I built for and tested on a virtme instance, 4/5 configs build and test sane as described, the 5th is probly dead from too many hacks. if you use git, and wanna just try it, you can find it here: git remote add .. # u dont need full clone https://github.com/jimc/linux.git dyndbg-diet branch I had good success with virtme, -q=-s -q=-S, and gdb target remote, all newbies should try it. These are on top of 5.8.0 +18 others, which GregKH added to his char-misc-testing &next trees. Jim Cromie (8): dyndbg: give %3u width in pr-format, cosmetic only dyndbg: motivate a diet plan dyndbg: select ZPOOL in Kconfig.debug dyndbg: split struct _ddebug in 2, creating _ddebug_callsite dyndbg: WIP replace __dyndbg_callsite section with a zs-pool copy. dyndbg: ddebug_zpool_remove dyndbg: enable 'cache' of active pr_debug callsites dyndbg: add locking around zpool-add loop in zpool-init include/asm-generic/vmlinux.lds.h | 4 + include/linux/dynamic_debug.h | 39 ++++-- lib/Kconfig.debug | 1 + lib/dynamic_debug.c | 223 +++++++++++++++++++++++++----- 4 files changed, 223 insertions(+), 44 deletions(-) -- 2.26.2

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Confusion about icsk_accept_queue
by tianyu chen Aug. 6, 2020

Aug. 6, 2020

When learning TCP three way handshake, I learn that TCP has a syn queue for those connections that haven't been established, and an accept queue for those who have been established. But I can only find one queue named *icsk_accept_queue* in *inet_connection_sock *struct, and I find that when the function *tcp_conn_request() *is called, the connection in the queue will be removed. But I haven't seen the connection being added to another queue. The accept() just return this connection. So I'm really confused. - Why is there only one queue *icsk_accept_queue?* - Is *icsk_accept_queue *the syn queue? - If it is, then where is the accept queue? Thanks for reading, hope for any possible help.

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CONFIG_KDB_KEYBOARD
by jim.cromie＠gmail.com Aug. 3, 2020

Aug. 3, 2020

.config - Linux/x86 5.8.0-rc7 Kernel Configuration > Kernel hacking > Generic Kernel Debugging Instruments > KGDB: kernel debugger KGDB_KDB: keyboard as input device \ │ CONFIG_KDB_KEYBOARD: │ KDB can use a PS/2 type keyboard for an input device │ I notice this excludes USB keyboard. does this mean it doesnt work early enough to be useful for early panics etc ? what does it mean for a panic right after starting 2nd CPUs ? [ 0.402982] smp: Bringing up secondary CPUs ... [ 0.403553] smp: Brought up 1 node, 1 CPU [ 0.404226] smpboot: Max logical packages: 1 [ 0.404552] smpboot: Total of 1 processors activated (5184.01 BogoMIPS) [ 0.406816] devtmpfs: initialized [ 0.408058] x86/mm: Memory block size: 128MB [ 0.416908] kthreadd invoked oom-killer: gfp_mask=0x2dc2(GFP_KERNEL|__GFP_HIGHMEM|__GFP_NOWARN|__GFP_ZERO), order=0, oom_score_adj=0 [ 0.417551] CPU: 0 PID: 2 Comm: kthreadd Not tainted 5.8.0-rc7-00023-gede6954dc460-dirty #101 [ 0.418541] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-2.fc32 04/01/2014 [ 0.418541] Call Trace: [ 0.418541] dump_stack+0x91/0xc8 [ 0.418541] dump_header+0x105/0x710 [ 0.418541] out_of_memory+0x63a/0x760 [ 0.418541] ? get_page_from_freelist+0x10b/0x950

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