linux-toradex.git/Documentation/sysctl, branch v4.10-rc7

Merge tag 'docs-4.10' of git://git.lwn.net/linux

2016-12-13T05:58:13+00:00

Pull documentation update from Jonathan Corbet:
 "These are the documentation changes for 4.10.

  It's another busy cycle for the docs tree, as the sphinx conversion
  continues. Highlights include:

   - Further work on PDF output, which remains a bit of a pain but
     should be more solid now.

   - Five more DocBook template files converted to Sphinx. Only 27 to
     go... Lots of plain-text files have also been converted and
     integrated.

   - Images in binary formats have been replaced with more
     source-friendly versions.

   - Various bits of organizational work, including the renaming of
     various files discussed at the kernel summit.

   - New documentation for the device_link mechanism.

  ... and, of course, lots of typo fixes and small updates"

* tag 'docs-4.10' of git://git.lwn.net/linux: (193 commits)
  dma-buf: Extract dma-buf.rst
  Update Documentation/00-INDEX
  docs: 00-INDEX: document directories/files with no docs
  docs: 00-INDEX: remove non-existing entries
  docs: 00-INDEX: add missing entries for documentation files/dirs
  docs: 00-INDEX: consolidate process/ and admin-guide/ description
  scripts: add a script to check if Documentation/00-INDEX is sane
  Docs: change sh -> awk in REPORTING-BUGS
  Documentation/core-api/device_link: Add initial documentation
  core-api: remove an unexpected unident
  ppc/idle: Add documentation for powersave=off
  Doc: Correct typo, "Introdution" => "Introduction"
  Documentation/atomic_ops.txt: convert to ReST markup
  Documentation/local_ops.txt: convert to ReST markup
  Documentation/assoc_array.txt: convert to ReST markup
  docs-rst: parse-headers.pl: cleanup the documentation
  docs-rst: fix media cleandocs target
  docs-rst: media/Makefile: reorganize the rules
  docs-rst: media: build SVG from graphviz files
  docs-rst: replace bayer.png by a SVG image
  ...

x86/dumpstack: Remove raw stack dump

2016-10-25T16:40:37+00:00

For mostly historical reasons, the x86 oops dump shows the raw stack
values:

  ...
  [registers]
  Stack:
   ffff880079af7350 ffff880079905400 0000000000000000 ffffc900008f3ae0
   ffffffffa0196610 0000000000000001 00010000ffffffff 0000000087654321
   0000000000000002 0000000000000000 0000000000000000 0000000000000000
  Call Trace:
  ...

This seems to be an artifact from long ago, and probably isn't needed
anymore.  It generally just adds noise to the dump, and it can be
actively harmful because it leaks kernel addresses.

Linus says:

  "The stack dump actually goes back to forever, and it used to be
   useful back in 1992 or so. But it used to be useful mainly because
   stacks were simpler and we didn't have very good call traces anyway. I
   definitely remember having used them - I just do not remember having
   used them in the last ten+ years.

   Of course, it's still true that if you can trigger an oops, you've
   likely already lost the security game, but since the stack dump is so
   useless, let's aim to just remove it and make games like the above
   harder."

This also removes the related 'kstack=' cmdline option and the
'kstack_depth_to_print' sysctl.

Suggested-by: Linus Torvalds 
Signed-off-by: Josh Poimboeuf 
Cc: Andy Lutomirski 
Cc: Borislav Petkov 
Cc: Brian Gerst 
Cc: Denys Vlasenko 
Cc: H. Peter Anvin 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/e83bd50df52d8fe88e94d2566426ae40d813bf8f.1477405374.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar

docs: fix locations of several documents that got moved

2016-10-24T10:12:35+00:00

The previous patch renamed several files that are cross-referenced
along the Kernel documentation. Adjust the links to point to
the right places.

Signed-off-by: Mauro Carvalho Chehab

mnt: Add a per mount namespace limit on the number of mounts

2016-09-30T17:46:48+00:00

CAI Qian  pointed out that the semantics
of shared subtrees make it possible to create an exponentially
increasing number of mounts in a mount namespace.

    mkdir /tmp/1 /tmp/2
    mount --make-rshared /
    for i in $(seq 1 20) ; do mount --bind /tmp/1 /tmp/2 ; done

Will create create 2^20 or 1048576 mounts, which is a practical problem
as some people have managed to hit this by accident.

As such CVE-2016-6213 was assigned.

Ian Kent  described the situation for autofs users
as follows:

> The number of mounts for direct mount maps is usually not very large because of
> the way they are implemented, large direct mount maps can have performance
> problems. There can be anywhere from a few (likely case a few hundred) to less
> than 10000, plus mounts that have been triggered and not yet expired.
>
> Indirect mounts have one autofs mount at the root plus the number of mounts that
> have been triggered and not yet expired.
>
> The number of autofs indirect map entries can range from a few to the common
> case of several thousand and in rare cases up to between 30000 and 50000. I've
> not heard of people with maps larger than 50000 entries.
>
> The larger the number of map entries the greater the possibility for a large
> number of active mounts so it's not hard to expect cases of a 1000 or somewhat
> more active mounts.

So I am setting the default number of mounts allowed per mount
namespace at 100,000.  This is more than enough for any use case I
know of, but small enough to quickly stop an exponential increase
in mounts.  Which should be perfect to catch misconfigurations and
malfunctioning programs.

For anyone who needs a higher limit this can be changed by writing
to the new /proc/sys/fs/mount-max sysctl.

Tested-by: CAI Qian 
Signed-off-by: "Eric W. Biederman"

userns; Document per user per user namespace limits.

2016-09-22T17:52:03+00:00

Signed-off-by: "Eric W. Biederman"

printk: add kernel parameter to control writes to /dev/kmsg

2016-08-02T23:35:06+00:00

Add a "printk.devkmsg" kernel command line parameter which controls how
userspace writes into /dev/kmsg.  It has three options:

 * ratelimit - ratelimit logging from userspace.
 * on  - unlimited logging from userspace
 * off - logging from userspace gets ignored

The default setting is to ratelimit the messages written to it.

This changes the kernel default setting of "on" to "ratelimit" and we do
that because we want to keep userspace spamming /dev/kmsg to sane
levels.  This is especially moot when a small kernel log buffer wraps
around and messages get lost.  So the ratelimiting setting should be a
sane setting where kernel messages should have a bit higher chance of
survival from all the spamming.

It additionally does not limit logging to /dev/kmsg while the system is
booting if we haven't disabled it on the command line.

Furthermore, we can control the logging from a lower priority sysctl
interface - kernel.printk_devkmsg.

That interface will succeed only if printk.devkmsg *hasn't* been
supplied on the command line.  If it has, then printk.devkmsg is a
one-time setting which remains for the duration of the system lifetime.
This "locking" of the setting is to prevent userspace from changing the
logging on us through sysctl(2).

This patch is based on previous patches from Linus and Steven.

[bp@suse.de: fixes]
  Link: http://lkml.kernel.org/r/20160719072344.GC25563@nazgul.tnic
Link: http://lkml.kernel.org/r/20160716061745.15795-3-bp@alien8.de
Signed-off-by: Borislav Petkov 
Cc: Dave Young 
Cc: Franck Bui 
Cc: Greg Kroah-Hartman 
Cc: Ingo Molnar 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Steven Rostedt 
Cc: Uwe Kleine-König 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

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

2016-07-26T20:05:11+00:00

Pull documentation updates from Jonathan Corbet:
 "Some big changes this month, headlined by the addition of a new
  formatted documentation mechanism based on the Sphinx system.

  The objectives here are to make it easier to create better-integrated
  (and more attractive) documents while (eventually) dumping our
  one-of-a-kind, cobbled-together system for something that is widely
  used and maintained by others.  There's a fair amount of information
  what's being done, why, and how to use it in:

    https://lwn.net/Articles/692704/
    https://lwn.net/Articles/692705/

  Closer to home, Documentation/kernel-documentation.rst describes how
  it works.

  For now, the new system exists alongside the old one; you should soon
  see the GPU documentation converted over in the DRM pull and some
  significant media conversion work as well.  Once all the docs have
  been moved over and we're convinced that the rough edges (of which are
  are a few) have been smoothed over, the DocBook-based stuff should go
  away.

  Primary credit is to Jani Nikula for doing the heavy lifting to make
  this stuff actually work; there has also been notable effort from
  Markus Heiser, Daniel Vetter, and Mauro Carvalho Chehab.

  Expect a couple of conflicts on the new index.rst file over the course
  of the merge window; they are trivially resolvable.  That file may be
  a bit of a conflict magnet in the short term, but I don't expect that
  situation to last for any real length of time.

  Beyond that, of course, we have the usual collection of tweaks,
  updates, and typo fixes"

* tag 'docs-for-linus' of git://git.lwn.net/linux: (77 commits)
  doc-rst: kernel-doc: fix handling of address_space tags
  Revert "doc/sphinx: Enable keep_warnings"
  doc-rst: kernel-doc directive, fix state machine reporter
  docs: deprecate kernel-doc-nano-HOWTO.txt
  doc/sphinx: Enable keep_warnings
  Documentation: add watermark_scale_factor to the list of vm systcl file
  kernel-doc: Fix up warning output
  docs: Get rid of some kernel-documentation warnings
  doc-rst: add an option to ignore DocBooks when generating docs
  workqueue: Fix a typo in workqueue.txt
  Doc: ocfs: Fix typo in filesystems/ocfs2-online-filecheck.txt
  Documentation/sphinx: skip build if user requested specific DOCBOOKS
  Documentation: add cleanmediadocs to the documentation targets
  Add .pyc files to .gitignore
  Doc: PM: Fix a typo in intel_powerclamp.txt
  doc-rst: flat-table directive - initial implementation
  Documentation: add meta-documentation for Sphinx and kernel-doc
  Documentation: tiny typo fix in usb/gadget_multi.txt
  Documentation: fix wrong value in md.txt
  bcache: documentation formatting, edited for clarity, stripe alignment notes
  ...

Documentation: add watermark_scale_factor to the list of vm systcl file

2016-07-18T14:27:01+00:00

Commit 795ae7a0de6b ("mm: scale kswapd watermarks in proportion to
memory") properly added the description of the new knob to
Documentation/sysctl/vm.txt, but forgot to add it to the list of files
in /proc/sys/vm. Let's fix that.

Signed-off-by: Jerome Marchand 
Acked-by: Johannes Weiner 
Signed-off-by: Jonathan Corbet

rcu: sysctl: Panic on RCU Stall

2016-06-15T23:00:05+00:00

It is not always easy to determine the cause of an RCU stall just by
analysing the RCU stall messages, mainly when the problem is caused
by the indirect starvation of rcu threads. For example, when preempt_rcu
is not awakened due to the starvation of a timer softirq.

We have been hard coding panic() in the RCU stall functions for
some time while testing the kernel-rt. But this is not possible in
some scenarios, like when supporting customers.

This patch implements the sysctl kernel.panic_on_rcu_stall. If
set to 1, the system will panic() when an RCU stall takes place,
enabling the capture of a vmcore. The vmcore provides a way to analyze
all kernel/tasks states, helping out to point to the culprit and the
solution for the stall.

The kernel.panic_on_rcu_stall sysctl is disabled by default.

Changes from v1:
- Fixed a typo in the git log
- The if(sysctl_panic_on_rcu_stall) panic() is in a static function
- Fixed the CONFIG_TINY_RCU compilation issue
- The var sysctl_panic_on_rcu_stall is now __read_mostly

Cc: Jonathan Corbet 
Cc: "Paul E. McKenney" 
Cc: Josh Triplett 
Cc: Steven Rostedt 
Cc: Mathieu Desnoyers 
Cc: Lai Jiangshan 
Acked-by: Christian Borntraeger 
Reviewed-by: Josh Triplett 
Reviewed-by: Arnaldo Carvalho de Melo 
Tested-by: "Luis Claudio R. Goncalves" 
Signed-off-by: Daniel Bristot de Oliveira 
Signed-off-by: Paul E. McKenney

Merge branch 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2016-05-26T00:05:40+00:00

Pull perf updates from Ingo Molnar:
 "Mostly tooling and PMU driver fixes, but also a number of late updates
  such as the reworking of the call-chain size limiting logic to make
  call-graph recording more robust, plus tooling side changes for the
  new 'backwards ring-buffer' extension to the perf ring-buffer"

* 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (34 commits)
  perf record: Read from backward ring buffer
  perf record: Rename variable to make code clear
  perf record: Prevent reading invalid data in record__mmap_read
  perf evlist: Add API to pause/resume
  perf trace: Use the ptr->name beautifier as default for "filename" args
  perf trace: Use the fd->name beautifier as default for "fd" args
  perf report: Add srcline_from/to branch sort keys
  perf evsel: Record fd into perf_mmap
  perf evsel: Add overwrite attribute and check write_backward
  perf tools: Set buildid dir under symfs when --symfs is provided
  perf trace: Only auto set call-graph to "dwarf" when syscalls are being traced
  perf annotate: Sort list of recognised instructions
  perf annotate: Fix identification of ARM blt and bls instructions
  perf tools: Fix usage of max_stack sysctl
  perf callchain: Stop validating callchains by the max_stack sysctl
  perf trace: Fix exit_group() formatting
  perf top: Use machine->kptr_restrict_warned
  perf trace: Warn when trying to resolve kernel addresses with kptr_restrict=1
  perf machine: Do not bail out if not managing to read ref reloc symbol
  perf/x86/intel/p4: Trival indentation fix, remove space
  ...