This documents the random directory, based on the behaviour seen in
drivers/char/random.c.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Link: https://lore.kernel.org/r/20200623112514.10650-1-steve@sk2.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Fix heading format warnings in admin-guide/sysctl/kernel.rst:
Documentation/admin-guide/sysctl/kernel.rst:339: WARNING: Title underline too short.
hung_task_all_cpu_backtrace:
================
Documentation/admin-guide/sysctl/kernel.rst:650: WARNING: Title underline too short.
oops_all_cpu_backtrace:
================
Fixes: 0ec9dc9bcb ("kernel/hung_task.c: introduce sysctl to print all traces when a hung task is detected")
Fixes: 60c958d8df ("panic: add sysctl to dump all CPUs backtraces on oops event")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/8af1cb77-4b5a-64b9-da5d-f6a95e537f99@infradead.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Usually when the kernel reaches an oops condition, it's a point of no
return; in case not enough debug information is available in the kernel
splat, one of the last resorts would be to collect a kernel crash dump
and analyze it. The problem with this approach is that in order to
collect the dump, a panic is required (to kexec-load the crash kernel).
When in an environment of multiple virtual machines, users may prefer to
try living with the oops, at least until being able to properly shutdown
their VMs / finish their important tasks.
This patch implements a way to collect a bit more debug details when an
oops event is reached, by printing all the CPUs backtraces through the
usage of NMIs (on architectures that support that). The sysctl added
(and documented) here was called "oops_all_cpu_backtrace", and when set
will (as the name suggests) dump all CPUs backtraces.
Far from ideal, this may be the last option though for users that for
some reason cannot panic on oops. Most of times oopses are clear enough
to indicate the kernel portion that must be investigated, but in virtual
environments it's possible to observe hypervisor/KVM issues that could
lead to oopses shown in other guests CPUs (like virtual APIC crashes).
This patch hence aims to help debug such complex issues without
resorting to kdump.
Signed-off-by: Guilherme G. Piccoli <gpiccoli@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: Iurii Zaikin <yzaikin@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Matthew Wilcox <willy@infradead.org>
Link: http://lkml.kernel.org/r/20200327224116.21030-1-gpiccoli@canonical.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Commit 401c636a0e ("kernel/hung_task.c: show all hung tasks before
panic") introduced a change in that we started to show all CPUs
backtraces when a hung task is detected _and_ the sysctl/kernel
parameter "hung_task_panic" is set. The idea is good, because usually
when observing deadlocks (that may lead to hung tasks), the culprit is
another task holding a lock and not necessarily the task detected as
hung.
The problem with this approach is that dumping backtraces is a slightly
expensive task, specially printing that on console (and specially in
many CPU machines, as servers commonly found nowadays). So, users that
plan to collect a kdump to investigate the hung tasks and narrow down
the deadlock definitely don't need the CPUs backtrace on dmesg/console,
which will delay the panic and pollute the log (crash tool would easily
grab all CPUs traces with 'bt -a' command).
Also, there's the reciprocal scenario: some users may be interested in
seeing the CPUs backtraces but not have the system panic when a hung
task is detected. The current approach hence is almost as embedding a
policy in the kernel, by forcing the CPUs backtraces' dump (only) on
hung_task_panic.
This patch decouples the panic event on hung task from the CPUs
backtraces dump, by creating (and documenting) a new sysctl called
"hung_task_all_cpu_backtrace", analog to the approach taken on soft/hard
lockups, that have both a panic and an "all_cpu_backtrace" sysctl to
allow individual control. The new mechanism for dumping the CPUs
backtraces on hung task detection respects "hung_task_warnings" by not
dumping the traces in case there's no warnings left.
Signed-off-by: Guilherme G. Piccoli <gpiccoli@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Link: http://lkml.kernel.org/r/20200327223646.20779-1-gpiccoli@canonical.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Analogously to the introduction of panic_on_warn, this patch introduces
a kernel option named panic_on_taint in order to provide a simple and
generic way to stop execution and catch a coredump when the kernel gets
tainted by any given flag.
This is useful for debugging sessions as it avoids having to rebuild the
kernel to explicitly add calls to panic() into the code sites that
introduce the taint flags of interest.
For instance, if one is interested in proceeding with a post-mortem
analysis at the point a given code path is hitting a bad page (i.e.
unaccount_page_cache_page(), or slab_bug()), a coredump can be collected
by rebooting the kernel with 'panic_on_taint=0x20' amended to the
command line.
Another, perhaps less frequent, use for this option would be as a means
for assuring a security policy case where only a subset of taints, or no
single taint (in paranoid mode), is allowed for the running system. The
optional switch 'nousertaint' is handy in this particular scenario, as
it will avoid userspace induced crashes by writes to sysctl interface
/proc/sys/kernel/tainted causing false positive hits for such policies.
[akpm@linux-foundation.org: tweak kernel-parameters.txt wording]
Suggested-by: Qian Cai <cai@lca.pw>
Signed-off-by: Rafael Aquini <aquini@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Cc: Dave Young <dyoung@redhat.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kees Cook <keescook@chromium.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Adrian Bunk <bunk@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Takashi Iwai <tiwai@suse.de>
Link: http://lkml.kernel.org/r/20200515175502.146720-1-aquini@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
set from Mauro toward the completion of the RST conversion. I *really*
hope we are getting close to the end of this. Meanwhile, those patches
reach pretty far afield to update document references around the tree;
there should be no actual code changes there. There will be, alas, more of
the usual trivial merge conflicts.
Beyond that we have more translations, improvements to the sphinx
scripting, a number of additions to the sysctl documentation, and lots of
fixes.
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Merge tag 'docs-5.8' of git://git.lwn.net/linux
Pull documentation updates from Jonathan Corbet:
"A fair amount of stuff this time around, dominated by yet another
massive set from Mauro toward the completion of the RST conversion. I
*really* hope we are getting close to the end of this. Meanwhile,
those patches reach pretty far afield to update document references
around the tree; there should be no actual code changes there. There
will be, alas, more of the usual trivial merge conflicts.
Beyond that we have more translations, improvements to the sphinx
scripting, a number of additions to the sysctl documentation, and lots
of fixes"
* tag 'docs-5.8' of git://git.lwn.net/linux: (130 commits)
Documentation: fixes to the maintainer-entry-profile template
zswap: docs/vm: Fix typo accept_threshold_percent in zswap.rst
tracing: Fix events.rst section numbering
docs: acpi: fix old http link and improve document format
docs: filesystems: add info about efivars content
Documentation: LSM: Correct the basic LSM description
mailmap: change email for Ricardo Ribalda
docs: sysctl/kernel: document unaligned controls
Documentation: admin-guide: update bug-hunting.rst
docs: sysctl/kernel: document ngroups_max
nvdimm: fixes to maintainter-entry-profile
Documentation/features: Correct RISC-V kprobes support entry
Documentation/features: Refresh the arch support status files
Revert "docs: sysctl/kernel: document ngroups_max"
docs: move locking-specific documents to locking/
docs: move digsig docs to the security book
docs: move the kref doc into the core-api book
docs: add IRQ documentation at the core-api book
docs: debugging-via-ohci1394.txt: add it to the core-api book
docs: fix references for ipmi.rst file
...
This documents ignore-unaligned-usertrap, unaligned-dump-stack, and
unaligned-trap, based on arch/arc/kernel/unaligned.c,
arch/ia64/kernel/unaligned.c, and arch/parisc/kernel/unaligned.c.
While we're at it, integrate unaligned-memory-access.txt into the docs
tree.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Link: https://lore.kernel.org/r/20200515212443.5012-1-steve@sk2.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This reverts commit 2f4c33063a.
The changes here were fine, but there's a non-documentation change to
sysctl.c that makes messes elsewhere; those changes should have been done
independently.
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This is a read-only export of NGROUPS_MAX, so this patch also changes
the declarations in kernel/sysctl.c to const.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20200515160222.7994-1-steve@sk2.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Based on the firmware fallback mechanisms documentation and the
implementation in drivers/base/firmware_loader/fallback.c.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Link: https://lore.kernel.org/r/20200429205757.8677-2-steve@sk2.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Based on the ftrace documentation, the tp_printk boot parameter
documentation, and the implementation in kernel/trace/trace.c.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20200429205757.8677-1-steve@sk2.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Based on the implementation in kernel/sysctl.c (the proc_do_cad_pid()
function), kernel/reboot.c, and include/linux/sched/signal.h.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Link: https://lore.kernel.org/r/20200423183651.15365-1-steve@sk2.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
kernel + tools/perf:
Alexey Budankov:
- Introduce CAP_PERFMON to kernel and user space.
callchains:
Adrian Hunter:
- Allow using Intel PT to synthesize callchains for regular events.
Kan Liang:
- Stitch LBR records from multiple samples to get deeper backtraces,
there are caveats, see the csets for details.
perf script:
Andreas Gerstmayr:
- Add flamegraph.py script
BPF:
Jiri Olsa:
- Synthesize bpf_trampoline/dispatcher ksymbol events.
perf stat:
Arnaldo Carvalho de Melo:
- Honour --timeout for forked workloads.
Stephane Eranian:
- Force error in fallback on :k events, to avoid counting nothing when
the user asks for kernel events but is not allowed to.
perf bench:
Ian Rogers:
- Add event synthesis benchmark.
tools api fs:
Stephane Eranian:
- Make xxx__mountpoint() more scalable
libtraceevent:
He Zhe:
- Handle return value of asprintf.
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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Merge tag 'perf-core-for-mingo-5.8-20200420' of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux into perf/core
Pull perf/core fixes and improvements from Arnaldo Carvalho de Melo:
kernel + tools/perf:
Alexey Budankov:
- Introduce CAP_PERFMON to kernel and user space.
callchains:
Adrian Hunter:
- Allow using Intel PT to synthesize callchains for regular events.
Kan Liang:
- Stitch LBR records from multiple samples to get deeper backtraces,
there are caveats, see the csets for details.
perf script:
Andreas Gerstmayr:
- Add flamegraph.py script
BPF:
Jiri Olsa:
- Synthesize bpf_trampoline/dispatcher ksymbol events.
perf stat:
Arnaldo Carvalho de Melo:
- Honour --timeout for forked workloads.
Stephane Eranian:
- Force error in fallback on :k events, to avoid counting nothing when
the user asks for kernel events but is not allowed to.
perf bench:
Ian Rogers:
- Add event synthesis benchmark.
tools api fs:
Stephane Eranian:
- Make xxx__mountpoint() more scalable
libtraceevent:
He Zhe:
- Handle return value of asprintf.
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Based on the implementation in kernel/bpf/syscall.c,
kernel/bpf/trampoline.c, include/linux/filter.h, and the documentation
in bpftool-prog.rst.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Link: https://lore.kernel.org/r/20200315122648.20558-1-steve@sk2.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Update the kernel.rst documentation file with the information related to
usage of CAP_PERFMON capability to secure performance monitoring and
observability operations in system.
Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Igor Lubashev <ilubashe@akamai.com>
Cc: James Morris <jmorris@namei.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Serge Hallyn <serge@hallyn.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: intel-gfx@lists.freedesktop.org
Cc: linux-doc@vger.kernel.org
Cc: linux-man@vger.kernel.org
Cc: linux-security-module@vger.kernel.org
Cc: selinux@vger.kernel.org
Link: http://lore.kernel.org/lkml/84c32383-14a2-fa35-16b6-f9e59bd37240@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Documentation for the kernel.modprobe sysctl was added both by
commit 0317c5371e ("docs: merge debugging-modules.txt into
sysctl/kernel.rst") and by commit 6e71582506 ("docs: admin-guide:
document the kernel.modprobe sysctl"), resulting in the same sysctl
being documented in two places. Merge these into one place.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Stephen Kitt <steve@sk2.org>
Link: https://lore.kernel.org/r/20200414172430.230293-1-ebiggers@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Document the kernel.modprobe sysctl in the same place that all the other
kernel.* sysctls are documented. Make sure to mention how to use this
sysctl to completely disable module autoloading, and how this sysctl
relates to CONFIG_STATIC_USERMODEHELPER.
[ebiggers@google.com: v5]
Link: http://lkml.kernel.org/r/20200318230515.171692-4-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jeff Vander Stoep <jeffv@google.com>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: NeilBrown <neilb@suse.com>
Link: http://lkml.kernel.org/r/20200312202552.241885-4-ebiggers@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Commit 9c44bc03ff ("softlockup: allow panic on lockup") added the
softlockup_panic sysctl, but didn't add information about it to the file
Documentation/admin-guide/sysctl/kernel.rst (which in that time certainly
wasn't rst and had other name!).
This patch just adds the respective documentation and references it from
the corresponding entry in Documentation/admin-guide/kernel-parameters.txt.
This patch was strongly based on Scott Wood's commit d22881dc13
("Documentation: Better document the hardlockup_panic sysctl").
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Guilherme G. Piccoli <gpiccoli@canonical.com>
Link: https://lore.kernel.org/r/20200310183649.23163-1-gpiccoli@canonical.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This script allows sysctl documentation to be checked against the
kernel source code, to identify missing or obsolete entries. Running
it against 5.5 shows for example that sysctl/kernel.rst has two
obsolete entries and is missing 52 entries.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Based on the implementation in arch/x86/kernel/acpi/sleep.c, in
particular the acpi_sleep_setup() function.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
The description of panic doesn’t cover all the supported scenarios;
this patch fixes that, describing the three possibilities (no reboot,
immediate reboot, reboot after a delay).
Based on the implementation in kernel/panic.c.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This describes the SPARC-specific stop-a sysctl entry, which was
previously listed in kernel.rst but not documented.
Base on the implementation in arch/sparc/kernel/setup_{32,64}.c and
kernel/panic.c.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This adds short descriptions of msgmax, msgmnb, msgmni, and shmmni,
which were previously listed in kernel.rst but not described.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
The l2cr sysctl entry was removed in commit c2f3dabefa ("sysctl:
kill binary sysctl KERN_PPC_L2CR"), this removes the corresponding
documentation.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This fits nicely in sysctl/kernel.rst, merge it (and rephrase it)
instead of linking to it.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This updates sysctl/kernel.rst to use ReStructured Text more fully:
* the list of files is now the table of contents (old entries with no
corresponding sections are added as empty sections for now);
* code references and commands are formatted as code, except for
function names which end up linked to the appropriate documentation;
* links are used to point to other documentation and other sections;
* tables are used to make lists of values more readable (as already
done for some sections);
* in heavily-reworked paragraphs, sentences are wrapped individually,
to make future diffs easier to read.
The first mention of the kernel version is dropped. The second
mention, saying that the document is accurate for 2.2, is preserved
for now; I will update that once the document really is accurate for a
current kernel release.
Signed-off-by: Stephen Kitt <steve@sk2.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
There is somehow no description of %c corename format specifier for
/proc/sys/kernel/core_pattern. The %c corename format specifier is
used by user-space application such as systemd-coredump, so it should
be documented.
To find where %c is handled in the kernel source code, look at
function format_corename() in fs/coredump.c.
Signed-off-by: HATAYAMA Daisuke <d.hatayama@fujitsu.com>
Link: https://lore.kernel.org/r/TYAPR01MB4014714BB2ACE425BB6EC6B7951A0@TYAPR01MB4014.jpnprd01.prod.outlook.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Since following path was merged in 5.4-rc3,
auto-tuning feature in threads-max does not exist any more.
Fix the admin-guide document as is.
kernel/sysctl.c: do not override max_threads provided by userspace
b0f53dbc4b
Fixes: b0f53dbc4b ("kernel/sysctl.c: do not override max_threads provided by userspace")
Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Since following patch was merged 5.4-rc3, minimum value for
threads-max changed to 1.
kernel/sysctl.c: do not override max_threads provided by userspace
b0f53dbc4b
Fixes: b0f53dbc4b ("kernel/sysctl.c: do not override max_threads provided by userspace")
Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
The printk_ratelimit value accepts seconds, not jiffies (though it is
converted into jiffies internally). Update documentation to reflect
this.
Also, remove the statement about allowing 1 message in 5 seconds since
bursts up to 10 messages are allowed by default.
Finally, while we are here, mention default value for
printk_ratelimit_burst too.
Signed-off-by: Oleksandr Natalenko <oleksandr@redhat.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
There are lots of documents that belong to the admin-guide but
are on random places (most under Documentation root dir).
Move them to the admin guide.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
The stuff under sysctl describes /sys interface from userspace
point of view. So, add it to the admin-guide and remove the
:orphan: from its index file.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Stephen Kitt