linux-toradex.git/Documentation/sysctl, branch v3.14.3

hung_task: check the value of "sysctl_hung_task_timeout_sec"

2014-05-06T14:59:35+00:00

commit 80df28476505ed4e6701c3448c63c9229a50c655 upstream.

As sysctl_hung_task_timeout_sec is unsigned long, when this value is
larger then LONG_MAX/HZ, the function schedule_timeout_interruptible in
watchdog will return immediately without sleep and with print :

  schedule_timeout: wrong timeout value ffffffffffffff83

and then the funtion watchdog will call schedule_timeout_interruptible
again and again.  The screen will be filled with

	"schedule_timeout: wrong timeout value ffffffffffffff83"

This patch does some check and correction in sysctl, to let the function
schedule_timeout_interruptible allways get the valid parameter.

Signed-off-by: Liu Hua 
Tested-by: Satoru Takeuchi 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

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

2014-01-31T16:59:46+00:00

Pull core debug changes from Ingo Molnar:
 "This contains mostly kernel debugging related updates:

   - make hung_task detection more configurable to distros
   - add final bits for x86 UV NMI debugging, with related KGDB changes
   - update the mailing-list of MAINTAINERS entries I'm involved with"

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  hung_task: Display every hung task warning
  sysctl: Add neg_one as a standard constraint
  x86/uv/nmi, kgdb/kdb: Fix UV NMI handler when KDB not configured
  x86/uv/nmi: Fix Sparse warnings
  kgdb/kdb: Fix no KDB config problem
  MAINTAINERS: Restore "L: linux-kernel@vger.kernel.org" entries

mm: document improved handling of swappiness==0

2014-01-30T00:22:39+00:00

Prior to commit fe35004fbf9e ("mm: avoid swapping out with
swappiness==0") setting swappiness to 0, reclaim code could still evict
recently used user anonymous memory to swap even though there is a
significant amount of RAM used for page cache.

The behaviour of setting swappiness to 0 has since changed.  When set,
the reclaim code does not initiate swap until the amount of free pages
and file-backed pages, is less than the high water mark in a zone.

Let's update the documentation to reflect this.

[akpm@linux-foundation.org: remove comma, per Randy]
Signed-off-by: Aaron Tomlin 
Acked-by: Rik van Riel 
Acked-by: Bryn M. Reeves 
Cc: Satoru Moriya 
Cc: Randy Dunlap 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

hung_task: Display every hung task warning

2014-01-25T11:13:33+00:00

When khungtaskd detects hung tasks, it prints out
backtraces from a number of those tasks.

Limiting the number of backtraces being printed
out can result in the user not seeing the information
necessary to debug the issue. The hung_task_warnings
sysctl controls this feature.

This patch makes it possible for hung_task_warnings
to accept a special value to print an unlimited
number of backtraces when khungtaskd detects hung
tasks.

The special value is -1. To use this value it is
necessary to change types from ulong to int.

Signed-off-by: Aaron Tomlin 
Reviewed-by: Rik van Riel 
Acked-by: David Rientjes 
Cc: oleg@redhat.com
Link: http://lkml.kernel.org/r/1390239253-24030-3-git-send-email-atomlin@redhat.com
[ Build warning fix. ]
Signed-off-by: Ingo Molnar

kexec: add sysctl to disable kexec_load

2014-01-24T00:37:03+00:00

For general-purpose (i.e.  distro) kernel builds it makes sense to build
with CONFIG_KEXEC to allow end users to choose what kind of things they
want to do with kexec.  However, in the face of trying to lock down a
system with such a kernel, there needs to be a way to disable kexec_load
(much like module loading can be disabled).  Without this, it is too easy
for the root user to modify kernel memory even when CONFIG_STRICT_DEVMEM
and modules_disabled are set.  With this change, it is still possible to
load an image for use later, then disable kexec_load so the image (or lack
of image) can't be altered.

The intention is for using this in environments where "perfect"
enforcement is hard.  Without a verified boot, along with verified
modules, and along with verified kexec, this is trying to give a system a
better chance to defend itself (or at least grow the window of
discoverability) against attack in the face of a privilege escalation.

In my mind, I consider several boot scenarios:

1) Verified boot of read-only verified root fs loading fd-based
   verification of kexec images.
2) Secure boot of writable root fs loading signed kexec images.
3) Regular boot loading kexec (e.g. kcrash) image early and locking it.
4) Regular boot with no control of kexec image at all.

1 and 2 don't exist yet, but will soon once the verified kexec series has
landed.  4 is the state of things now.  The gap between 2 and 4 is too
large, so this change creates scenario 3, a middle-ground above 4 when 2
and 1 are not possible for a system.

Signed-off-by: Kees Cook 
Acked-by: Rik van Riel 
Cc: Vivek Goyal 
Cc: Eric Biederman 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: add overcommit_kbytes sysctl variable

2014-01-22T00:19:44+00:00

Some applications that run on HPC clusters are designed around the
availability of RAM and the overcommit ratio is fine tuned to get the
maximum usage of memory without swapping.  With growing memory, the
1%-of-all-RAM grain provided by overcommit_ratio has become too coarse
for these workload (on a 2TB machine it represents no less than 20GB).

This patch adds the new overcommit_kbytes sysctl variable that allow a
much finer grain.

[akpm@linux-foundation.org: coding-style fixes]
[akpm@linux-foundation.org: fix nommu build]
Signed-off-by: Jerome Marchand 
Cc: Dave Hansen 
Cc: Alan Cox 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

sched/numa: Drop sysctl_numa_balancing_settle_count sysctl

2013-12-17T14:24:38+00:00

commit 887c290e (sched/numa: Decide whether to favour task or group weights
based on swap candidate relationships) drop the check against
sysctl_numa_balancing_settle_count, this patch remove the sysctl.

Signed-off-by: Wanpeng Li 
Acked-by: Mel Gorman 
Reviewed-by: Rik van Riel 
Acked-by: David Rientjes 
Signed-off-by: Peter Zijlstra 
Cc: Andrew Morton 
Cc: Naoya Horiguchi 
Link: http://lkml.kernel.org/r/1386833006-6600-1-git-send-email-liwanp@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar

vsprintf: check real user/group id for %pK

2013-11-13T03:09:14+00:00

Some setuid binaries will allow reading of files which have read
permission by the real user id.  This is problematic with files which
use %pK because the file access permission is checked at open() time,
but the kptr_restrict setting is checked at read() time.  If a setuid
binary opens a %pK file as an unprivileged user, and then elevates
permissions before reading the file, then kernel pointer values may be
leaked.

This happens for example with the setuid pppd application on Ubuntu 12.04:

  $ head -1 /proc/kallsyms
  00000000 T startup_32

  $ pppd file /proc/kallsyms
  pppd: In file /proc/kallsyms: unrecognized option 'c1000000'

This will only leak the pointer value from the first line, but other
setuid binaries may leak more information.

Fix this by adding a check that in addition to the current process having
CAP_SYSLOG, that effective user and group ids are equal to the real ids.
If a setuid binary reads the contents of a file which uses %pK then the
pointer values will be printed as NULL if the real user is unprivileged.

Update the sysctl documentation to reflect the changes, and also correct
the documentation to state the kptr_restrict=0 is the default.

This is a only temporary solution to the issue.  The correct solution is
to do the permission check at open() time on files, and to replace %pK
with a function which checks the open() time permission.  %pK uses in
printk should be removed since no sane permission check can be done, and
instead protected by using dmesg_restrict.

Signed-off-by: Ryan Mallon 
Cc: Kees Cook 
Cc: Alexander Viro 
Cc: Joe Perches 
Cc: "Eric W. Biederman" 
Cc: 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: improve the description for dirty_background_ratio/dirty_ratio sysctl

2013-11-13T03:09:11+00:00

Now dirty_background_ratio/dirty_ratio contains a percentage of total
avaiable memory, which contains free pages and reclaimable pages.  The
number of these pages is not equal to the number of total system memory.
But they are described as a percentage of total system memory in
Documentation/sysctl/vm.txt.  So we need to fix them to avoid
misunderstanding.

Signed-off-by: Zheng Liu 
Cc: Rob Landley 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

sched/numa: Skip some page migrations after a shared fault

2013-10-09T12:48:21+00:00

Shared faults can lead to lots of unnecessary page migrations,
slowing down the system, and causing private faults to hit the
per-pgdat migration ratelimit.

This patch adds sysctl numa_balancing_migrate_deferred, which specifies
how many shared page migrations to skip unconditionally, after each page
migration that is skipped because it is a shared fault.

This reduces the number of page migrations back and forth in
shared fault situations. It also gives a strong preference to
the tasks that are already running where most of the memory is,
and to moving the other tasks to near the memory.

Testing this with a much higher scan rate than the default
still seems to result in fewer page migrations than before.

Memory seems to be somewhat better consolidated than previously,
with multi-instance specjbb runs on a 4 node system.

Signed-off-by: Rik van Riel 
Signed-off-by: Mel Gorman 
Cc: Andrea Arcangeli 
Cc: Johannes Weiner 
Cc: Srikar Dronamraju 
Signed-off-by: Peter Zijlstra 
Link: http://lkml.kernel.org/r/1381141781-10992-62-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar