linux-toradex.git/Documentation/admin-guide/sysctl, branch v6.19-rc2

Merge tag 'mm-nonmm-stable-2025-12-06-11-14' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

2025-12-06T22:01:20+00:00

Pull non-MM updates from Andrew Morton:

 - "panic: sys_info: Refactor and fix a potential issue" (Andy Shevchenko)
   fixes a build issue and does some cleanup in ib/sys_info.c

 - "Implement mul_u64_u64_div_u64_roundup()" (David Laight)
   enhances the 64-bit math code on behalf of a PWM driver and beefs up
   the test module for these library functions

 - "scripts/gdb/symbols: make BPF debug info available to GDB" (Ilya Leoshkevich)
   makes BPF symbol names, sizes, and line numbers available to the GDB
   debugger

 - "Enable hung_task and lockup cases to dump system info on demand" (Feng Tang)
   adds a sysctl which can be used to cause additional info dumping when
   the hung-task and lockup detectors fire

 - "lib/base64: add generic encoder/decoder, migrate users" (Kuan-Wei Chiu)
   adds a general base64 encoder/decoder to lib/ and migrates several
   users away from their private implementations

 - "rbree: inline rb_first() and rb_last()" (Eric Dumazet)
   makes TCP a little faster

 - "liveupdate: Rework KHO for in-kernel users" (Pasha Tatashin)
   reworks the KEXEC Handover interfaces in preparation for Live Update
   Orchestrator (LUO), and possibly for other future clients

 - "kho: simplify state machine and enable dynamic updates" (Pasha Tatashin)
   increases the flexibility of KEXEC Handover. Also preparation for LUO

 - "Live Update Orchestrator" (Pasha Tatashin)
   is a major new feature targeted at cloud environments. Quoting the
   cover letter:

      This series introduces the Live Update Orchestrator, a kernel
      subsystem designed to facilitate live kernel updates using a
      kexec-based reboot. This capability is critical for cloud
      environments, allowing hypervisors to be updated with minimal
      downtime for running virtual machines. LUO achieves this by
      preserving the state of selected resources, such as memory,
      devices and their dependencies, across the kernel transition.

      As a key feature, this series includes support for preserving
      memfd file descriptors, which allows critical in-memory data, such
      as guest RAM or any other large memory region, to be maintained in
      RAM across the kexec reboot.

   Mike Rappaport merits a mention here, for his extensive review and
   testing work.

 - "kexec: reorganize kexec and kdump sysfs" (Sourabh Jain)
   moves the kexec and kdump sysfs entries from /sys/kernel/ to
   /sys/kernel/kexec/ and adds back-compatibility symlinks which can
   hopefully be removed one day

 - "kho: fixes for vmalloc restoration" (Mike Rapoport)
   fixes a BUG which was being hit during KHO restoration of vmalloc()
   regions

* tag 'mm-nonmm-stable-2025-12-06-11-14' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm: (139 commits)
  calibrate: update header inclusion
  Reinstate "resource: avoid unnecessary lookups in find_next_iomem_res()"
  vmcoreinfo: track and log recoverable hardware errors
  kho: fix restoring of contiguous ranges of order-0 pages
  kho: kho_restore_vmalloc: fix initialization of pages array
  MAINTAINERS: TPM DEVICE DRIVER: update the W-tag
  init: replace simple_strtoul with kstrtoul to improve lpj_setup
  KHO: fix boot failure due to kmemleak access to non-PRESENT pages
  Documentation/ABI: new kexec and kdump sysfs interface
  Documentation/ABI: mark old kexec sysfs deprecated
  kexec: move sysfs entries to /sys/kernel/kexec
  test_kho: always print restore status
  kho: free chunks using free_page() instead of kfree()
  selftests/liveupdate: add kexec test for multiple and empty sessions
  selftests/liveupdate: add simple kexec-based selftest for LUO
  selftests/liveupdate: add userspace API selftests
  docs: add documentation for memfd preservation via LUO
  mm: memfd_luo: allow preserving memfd
  liveupdate: luo_file: add private argument to store runtime state
  mm: shmem: export some functions to internal.h
  ...

sys_info: add a default kernel sys_info mask

2025-11-20T22:03:43+00:00

Which serves as a global default sys_info mask.  When users want the same
system information for many error cases (panic, hung, lockup ...), they
can chose to set this global knob only once, while not setting up each
individual sys_info knobs.

This just adds a 'lazy' option, and doesn't change existing kernel
behavior as the mask is 0 by default.

Link: https://lkml.kernel.org/r/20251113111039.22701-5-feng.tang@linux.alibaba.com
Suggested-by: Andrew Morton 
Signed-off-by: Feng Tang 
Cc: Jonathan Corbet 
Cc: Lance Yang 
Cc: "Paul E . McKenney" 
Cc: Petr Mladek 
Cc: Steven Rostedt 
Signed-off-by: Andrew Morton

watchdog: add sys_info sysctls to dump sys info on system lockup

2025-11-20T22:03:43+00:00

When soft/hard lockup happens, developers may need different kinds of
system information (call-stacks, memory info, locks, etc.) to help
debugging.

Add 'softlockup_sys_info' and 'hardlockup_sys_info' sysctl knobs to take
human readable string like "tasks,mem,timers,locks,ftrace,...", and when
system lockup happens, all requested information will be printed out. 
(refer kernel/sys_info.c for more details).

Link: https://lkml.kernel.org/r/20251113111039.22701-4-feng.tang@linux.alibaba.com
Signed-off-by: Feng Tang 
Reviewed-by: Petr Mladek 
Cc: Jonathan Corbet 
Cc: Lance Yang 
Cc: "Paul E . McKenney" 
Cc: Petr Mladek 
Cc: Steven Rostedt 
Signed-off-by: Andrew Morton

hung_task: add hung_task_sys_info sysctl to dump sys info on task-hung

2025-11-20T22:03:43+00:00

When task-hung happens, developers may need different kinds of system
information (call-stacks, memory info, locks, etc.) to help debugging.

Add 'hung_task_sys_info' sysctl knob to take human readable string like
"tasks,mem,timers,locks,ftrace,...", and when task-hung happens, all
requested information will be dumped.  (refer kernel/sys_info.c for more
details).

Meanwhile, the newly introduced sys_info() call is used to unify some
existing info-dumping knobs.

[feng.tang@linux.alibaba.com: maintain consistecy established behavior, per Lance and Petr]
  Link: https://lkml.kernel.org/r/aRncJo1mA5Zk77Hr@U-2FWC9VHC-2323.local
Link: https://lkml.kernel.org/r/20251113111039.22701-3-feng.tang@linux.alibaba.com
Signed-off-by: Feng Tang 
Suggested-by: Petr Mladek 
Reviewed-by: Petr Mladek 
Reviewed-by: Lance Yang 
Cc: Jonathan Corbet 
Cc: "Paul E . McKenney" 
Cc: Steven Rostedt 
Signed-off-by: Andrew Morton

docs: panic: correct some sys_ifo names in sysctl doc

2025-11-20T22:03:43+00:00

Patch series "Enable hung_task and lockup cases to dump system info on
demand", v2.

When working on kernel stability issues: panic, task-hung and soft/hard
lockup are frequently met.  And to debug them, user may need lots of
system information at that time, like task call stacks, lock info, memory
info, ftrace dump, etc.

panic case already uses sys_info() for this purpose, and has a
'panic_sys_info' sysctl(also support cmdline setup) interface to take
human readable string like "tasks,mem,timers,locks,ftrace,..." to control
what kinds of information is needed.  Which is also helpful to debug
task-hung and lockup cases.

So this patchset introduces the similar sys_info sysctl interface for
task-hung and lockup cases.

his is mainly for debugging and the info dumping could be intrusive, like
dumping call stack for all tasks when system has huge number of tasks,
similarly for ftrace dump (we may add tracing_stop() and tracing_start()
around it)

Locally these have been used in our bug chasing for stability issues and
were helpful.

As Andrew suggested, add a configurable global 'kernel_sys_info' knob. 
When error scenarios like panic/hung-task/lockup etc doesn't setup their
own sys_info knob and calls sys_info() with parameter "0", this global
knob will take effect.  It could be used for other kernel cases like OOM,
which may not need one dedicated sys_info knob.


This patch (of 4):

Some sys_info names wered forgotten to change in patch iterations, while
the right names are defined in kernel/sys_info.c.

Link: https://lkml.kernel.org/r/20251113111039.22701-1-feng.tang@linux.alibaba.com
Link: https://lkml.kernel.org/r/20251113111039.22701-2-feng.tang@linux.alibaba.com
Fixes: d747755917bf ("panic: add 'panic_sys_info' sysctl to take human readable string parameter")
Signed-off-by: Feng Tang 
Reviewed-by: Petr Mladek 
Cc: Jonathan Corbet 
Cc: Lance Yang 
Cc: "Paul E . McKenney" 
Cc: Steven Rostedt 
Signed-off-by: Andrew Morton

hung_task: panic when there are more than N hung tasks at the same time

2025-11-12T18:00:14+00:00

The hung_task_panic sysctl is currently a blunt instrument: it's all or
nothing.

Panicking on a single hung task can be an overreaction to a transient
glitch.  A more reliable indicator of a systemic problem is when
multiple tasks hang simultaneously.

Extend hung_task_panic to accept an integer threshold, allowing the
kernel to panic only when N hung tasks are detected in a single scan. 
This provides finer control to distinguish between isolated incidents
and system-wide failures.

The accepted values are:
- 0: Don't panic (unchanged)
- 1: Panic on the first hung task (unchanged)
- N > 1: Panic after N hung tasks are detected in a single scan

The original behavior is preserved for values 0 and 1, maintaining full
backward compatibility.

[lance.yang@linux.dev: new changelog]
Link: https://lkml.kernel.org/r/20251015063615.2632-1-lirongqing@baidu.com
Signed-off-by: Li RongQing 
Reviewed-by: Masami Hiramatsu (Google) 
Reviewed-by: Lance Yang 
Tested-by: Lance Yang 
Acked-by: Andrew Jeffery  [aspeed_g5_defconfig]
Cc: Anshuman Khandual 
Cc: Arnd Bergmann 
Cc: David Hildenbrand 
Cc: Florian Wesphal 
Cc: Jakub Kacinski 
Cc: Jason A. Donenfeld 
Cc: Joel Granados 
Cc: Joel Stanley 
Cc: Jonathan Corbet 
Cc: Kees Cook 
Cc: Liam Howlett 
Cc: Lorenzo Stoakes 
Cc: "Paul E . McKenney" 
Cc: Pawan Gupta 
Cc: Petr Mladek 
Cc: Phil Auld 
Cc: Randy Dunlap 
Cc: Russell King 
Cc: Shuah Khan 
Cc: Simon Horman 
Cc: Stanislav Fomichev 
Cc: Steven Rostedt 
Signed-off-by: Andrew Morton

net: increase skb_defer_max default to 128

2025-11-08T03:02:40+00:00

skb_defer_max value is very conservative, and can be increased
to avoid too many calls to kick_defer_list_purge().

Signed-off-by: Eric Dumazet 
Reviewed-by: Kuniyuki Iwashima 
Reviewed-by: Toke Høiland-Jørgensen 
Reviewed-by: Jason Xing 
Link: https://patch.msgid.link/20251106202935.1776179-4-edumazet@google.com
Signed-off-by: Jakub Kicinski

net: Introduce net.core.bypass_prot_mem sysctl.

2025-10-16T19:04:47+00:00

If a socket has sk->sk_bypass_prot_mem flagged, the socket opts out
of the global protocol memory accounting.

Let's control the flag by a new sysctl knob.

The flag is written once during socket(2) and is inherited to child
sockets.

Tested with a script that creates local socket pairs and send()s a
bunch of data without recv()ing.

Setup:

  # mkdir /sys/fs/cgroup/test
  # echo $$ >> /sys/fs/cgroup/test/cgroup.procs
  # sysctl -q net.ipv4.tcp_mem="1000 1000 1000"
  # ulimit -n 524288

Without net.core.bypass_prot_mem, charged to tcp_mem & memcg

  # python3 pressure.py &
  # cat /sys/fs/cgroup/test/memory.stat | grep sock
  sock 22642688 <-------------------------------------- charged to memcg
  # cat /proc/net/sockstat| grep TCP
  TCP: inuse 2006 orphan 0 tw 0 alloc 2008 mem 5376 <-- charged to tcp_mem
  # ss -tn | head -n 5
  State Recv-Q Send-Q Local Address:Port  Peer Address:Port
  ESTAB 2000   0          127.0.0.1:34479    127.0.0.1:53188
  ESTAB 2000   0          127.0.0.1:34479    127.0.0.1:49972
  ESTAB 2000   0          127.0.0.1:34479    127.0.0.1:53868
  ESTAB 2000   0          127.0.0.1:34479    127.0.0.1:53554
  # nstat | grep Pressure || echo no pressure
  TcpExtTCPMemoryPressures        1                  0.0

With net.core.bypass_prot_mem=1, charged to memcg only:

  # sysctl -q net.core.bypass_prot_mem=1
  # python3 pressure.py &
  # cat /sys/fs/cgroup/test/memory.stat | grep sock
  sock 2757468160 <------------------------------------ charged to memcg
  # cat /proc/net/sockstat | grep TCP
  TCP: inuse 2006 orphan 0 tw 0 alloc 2008 mem 0 <- NOT charged to tcp_mem
  # ss -tn | head -n 5
  State Recv-Q Send-Q  Local Address:Port  Peer Address:Port
  ESTAB 111000 0           127.0.0.1:36019    127.0.0.1:49026
  ESTAB 110000 0           127.0.0.1:36019    127.0.0.1:45630
  ESTAB 110000 0           127.0.0.1:36019    127.0.0.1:44870
  ESTAB 111000 0           127.0.0.1:36019    127.0.0.1:45274
  # nstat | grep Pressure || echo no pressure
  no pressure

Signed-off-by: Kuniyuki Iwashima 
Signed-off-by: Martin KaFai Lau 
Reviewed-by: Shakeel Butt 
Reviewed-by: Eric Dumazet 
Acked-by: Roman Gushchin 
Link: https://patch.msgid.link/20251014235604.3057003-4-kuniyu@google.com

net: add /proc/sys/net/core/txq_reselection_ms control

2025-10-15T16:04:21+00:00

Add a new sysctl to control how often a queue reselection
can happen even if a flow has a persistent queue of skbs
in a Qdisc or NIC queue.

A value of zero means the feature is disabled.

Default is 1000 (1 second).

This sysctl is used in the following patch.

Signed-off-by: Eric Dumazet 
Reviewed-by: Neal Cardwell 
Reviewed-by: Kuniyuki Iwashima 
Link: https://patch.msgid.link/20251013152234.842065-4-edumazet@google.com
Signed-off-by: Jakub Kicinski

Merge tag 'docs-6.18' of git://git.lwn.net/linux

2025-10-04T00:16:13+00:00

Pull documentation updates from Jonathan Corbet:
 "It has been a relatively busy cycle in docsland, with changes all
  over:

   - Bring the kernel memory-model docs into the Sphinx build in the
     "literal include" mode.

   - Lots of build-infrastructure work, further cleaning up long-term
     kernel-doc technical debt. The sphinx-pre-install tool has been
     converted to Python and updated for current systems.

   - A new tool to detect when documents have been moved and generate
     HTML redirects; this can be used on kernel.org (or any other site
     hosting the rendered docs) to avoid breaking links.

   - Automated processing of the YAML files describing the netlink
     protocol.

   - A significant update of the maintainer's PGP guide.

  ... and a seemingly endless series of typo fixes, build-problem fixes,
  etc"

* tag 'docs-6.18' of git://git.lwn.net/linux: (193 commits)
  Documentation/features: Update feature lists for 6.17-rc7
  docs: remove cdomain.py
  Documentation/process: submitting-patches: fix typo in "were do"
  docs: dev-tools/lkmm: Fix typo of missing file extension
  Documentation: trace: histogram: Convert ftrace docs cross-reference
  Documentation: trace: histogram-design: Wrap introductory note in note:: directive
  Documentation: trace: historgram-design: Separate sched_waking histogram section heading and the following diagram
  Documentation: trace: histogram-design: Trim trailing vertices in diagram explanation text
  Documentation: trace: histogram: Fix histogram trigger subsection number order
  docs: driver-api: fix spelling of "buses".
  Documentation: fbcon: Use admonition directives
  Documentation: fbcon: Reindent 8th step of attach/detach/unload
  Documentation: fbcon: Add boot options and attach/detach/unload section headings
  docs: filesystems: sysfs: add remaining top level sysfs directory descriptions
  docs: filesystems: sysfs: clarify symlink destinations in dev and bus/devices descriptions
  docs: filesystems: sysfs: remove top level sysfs net directory
  docs: maintainer: Fix ambiguous subheading formatting
  docs: kdoc: a few more dump_typedef() tweaks
  docs: kdoc: remove redundant comment stripping in dump_typedef()
  docs: kdoc: remove some dead code in dump_typedef()
  ...