linux.git/Documentation/admin-guide, branch v5.8-rc2

Merge tag 'docs-5.8-2' of git://git.lwn.net/linux

2020-06-10T21:12:15+00:00

Pull more documentation updates from Jonathan Corbet:
 "A handful of late-arriving docs fixes, along with a patch changing a
  lot of HTTP links to HTTPS that had to be yanked and redone before the
  first pull"

* tag 'docs-5.8-2' of git://git.lwn.net/linux:
  docs/memory-barriers.txt/kokr: smp_mb__{before,after}_atomic(): update Documentation
  Documentation: devres: add missing entry for devm_platform_get_and_ioremap_resource()
  Replace HTTP links with HTTPS ones: documentation
  docs: it_IT: address invalid reference warnings
  doc: zh_CN: use doc reference to resolve undefined label warning
  docs: Update the location of the LF NDA program
  docs: dev-tools: coccinelle: underlines

Merge branch 'akpm' (patches from Andrew)

2020-06-09T16:54:46+00:00

Merge even more updates from Andrew Morton:

 - a kernel-wide sweep of show_stack()

 - pagetable cleanups

 - abstract out accesses to mmap_sem - prep for mmap_sem scalability work

 - hch's user acess work

Subsystems affected by this patch series: debug, mm/pagemap, mm/maccess,
mm/documentation.

* emailed patches from Andrew Morton : (93 commits)
  include/linux/cache.h: expand documentation over __read_mostly
  maccess: return -ERANGE when probe_kernel_read() fails
  x86: use non-set_fs based maccess routines
  maccess: allow architectures to provide kernel probing directly
  maccess: move user access routines together
  maccess: always use strict semantics for probe_kernel_read
  maccess: remove strncpy_from_unsafe
  tracing/kprobes: handle mixed kernel/userspace probes better
  bpf: rework the compat kernel probe handling
  bpf:bpf_seq_printf(): handle potentially unsafe format string better
  bpf: handle the compat string in bpf_trace_copy_string better
  bpf: factor out a bpf_trace_copy_string helper
  maccess: unify the probe kernel arch hooks
  maccess: remove probe_read_common and probe_write_common
  maccess: rename strnlen_unsafe_user to strnlen_user_nofault
  maccess: rename strncpy_from_unsafe_strict to strncpy_from_kernel_nofault
  maccess: rename strncpy_from_unsafe_user to strncpy_from_user_nofault
  maccess: update the top of file comment
  maccess: clarify kerneldoc comments
  maccess: remove duplicate kerneldoc comments
  ...

mmap locking API: convert mmap_sem comments

2020-06-09T16:39:14+00:00

Convert comments that reference mmap_sem to reference mmap_lock instead.

[akpm@linux-foundation.org: fix up linux-next leftovers]
[akpm@linux-foundation.org: s/lockaphore/lock/, per Vlastimil]
[akpm@linux-foundation.org: more linux-next fixups, per Michel]

Signed-off-by: Michel Lespinasse 
Signed-off-by: Andrew Morton 
Reviewed-by: Vlastimil Babka 
Reviewed-by: Daniel Jordan 
Cc: Davidlohr Bueso 
Cc: David Rientjes 
Cc: Hugh Dickins 
Cc: Jason Gunthorpe 
Cc: Jerome Glisse 
Cc: John Hubbard 
Cc: Laurent Dufour 
Cc: Liam Howlett 
Cc: Matthew Wilcox 
Cc: Peter Zijlstra 
Cc: Ying Han 
Link: http://lkml.kernel.org/r/20200520052908.204642-13-walken@google.com
Signed-off-by: Linus Torvalds

Merge branch 'x86/srbds' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2020-06-09T16:30:21+00:00

Pull x86 srbds fixes from Thomas Gleixner:
 "The 9th episode of the dime novel "The performance killer" with the
  subtitle "Slow Randomizing Boosts Denial of Service".

  SRBDS is an MDS-like speculative side channel that can leak bits from
  the random number generator (RNG) across cores and threads. New
  microcode serializes the processor access during the execution of
  RDRAND and RDSEED. This ensures that the shared buffer is overwritten
  before it is released for reuse. This is equivalent to a full bus
  lock, which means that many threads running the RNG instructions in
  parallel have the same effect as the same amount of threads issuing a
  locked instruction targeting an address which requires locking of two
  cachelines at once.

  The mitigation support comes with the usual pile of unpleasant
  ingredients:

   - command line options

   - sysfs file

   - microcode checks

   - a list of vulnerable CPUs identified by model and stepping this
     time which requires stepping match support for the cpu match logic.

   - the inevitable slowdown of affected CPUs"

* branch 'x86/srbds' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/speculation: Add Ivy Bridge to affected list
  x86/speculation: Add SRBDS vulnerability and mitigation documentation
  x86/speculation: Add Special Register Buffer Data Sampling (SRBDS) mitigation
  x86/cpu: Add 'table' argument to cpu_matches()

Merge tag 's390-5.8-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux

2020-06-08T19:05:31+00:00

Pull s390 updates from Vasily Gorbik:

 - Add support for multi-function devices in pci code.

 - Enable PF-VF linking for architectures using the pdev->no_vf_scan
   flag (currently just s390).

 - Add reipl from NVMe support.

 - Get rid of critical section cleanup in entry.S.

 - Refactor PNSO CHSC (perform network subchannel operation) in cio and
   qeth.

 - QDIO interrupts and error handling fixes and improvements, more
   refactoring changes.

 - Align ioremap() with generic code.

 - Accept requests without the prefetch bit set in vfio-ccw.

 - Enable path handling via two new regions in vfio-ccw.

 - Other small fixes and improvements all over the code.

* tag 's390-5.8-1' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux: (52 commits)
  vfio-ccw: make vfio_ccw_regops variables declarations static
  vfio-ccw: Add trace for CRW event
  vfio-ccw: Wire up the CRW irq and CRW region
  vfio-ccw: Introduce a new CRW region
  vfio-ccw: Refactor IRQ handlers
  vfio-ccw: Introduce a new schib region
  vfio-ccw: Refactor the unregister of the async regions
  vfio-ccw: Register a chp_event callback for vfio-ccw
  vfio-ccw: Introduce new helper functions to free/destroy regions
  vfio-ccw: document possible errors
  vfio-ccw: Enable transparent CCW IPL from DASD
  s390/pci: Log new handle in clp_disable_fh()
  s390/cio, s390/qeth: cleanup PNSO CHSC
  s390/qdio: remove q->first_to_kick
  s390/qdio: fix up qdio_start_irq() kerneldoc
  s390: remove critical section cleanup from entry.S
  s390: add machine check SIGP
  s390/pci: ioremap() align with generic code
  s390/ap: introduce new ap function ap_get_qdev()
  Documentation/s390: Update / remove developerWorks web links
  ...

doc: cgroup: update note about conditions when oom killer is invoked

2020-06-08T18:05:58+00:00

Starting from v4.19 commit 29ef680ae7c2 ("memcg, oom: move out_of_memory
back to the charge path") cgroup oom killer is no longer invoked only
from page faults.  Now it implements the same semantics as global OOM
killer: allocation context invokes OOM killer and keeps retrying until
success.

[akpm@linux-foundation.org: fixes per Randy]

Signed-off-by: Konstantin Khlebnikov 
Signed-off-by: Andrew Morton 
Acked-by: Michal Hocko 
Cc: Roman Gushchin 
Cc: Randy Dunlap 
Link: http://lkml.kernel.org/r/158894738928.208854.5244393925922074518.stgit@buzz
Signed-off-by: Linus Torvalds

panic: add sysctl to dump all CPUs backtraces on oops event

2020-06-08T18:05:56+00:00

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 
Signed-off-by: Andrew Morton 
Reviewed-by: Kees Cook 
Cc: Luis Chamberlain 
Cc: Iurii Zaikin 
Cc: Thomas Gleixner 
Cc: Vlastimil Babka 
Cc: Randy Dunlap 
Cc: Matthew Wilcox 
Link: http://lkml.kernel.org/r/20200327224116.21030-1-gpiccoli@canonical.com
Signed-off-by: Linus Torvalds

kernel/hung_task.c: introduce sysctl to print all traces when a hung task is detected

2020-06-08T18:05:56+00:00

Commit 401c636a0eeb ("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 
Signed-off-by: Andrew Morton 
Reviewed-by: Kees Cook 
Cc: Tetsuo Handa 
Link: http://lkml.kernel.org/r/20200327223646.20779-1-gpiccoli@canonical.com
Signed-off-by: Linus Torvalds

kernel/watchdog.c: convert {soft/hard}lockup boot parameters to sysctl aliases

2020-06-08T18:05:56+00:00

After a recent change introduced by Vlastimil's series [0], kernel is
able now to handle sysctl parameters on kernel command line; also, the
series introduced a simple infrastructure to convert legacy boot
parameters (that duplicate sysctls) into sysctl aliases.

This patch converts the watchdog parameters softlockup_panic and
{hard,soft}lockup_all_cpu_backtrace to use the new alias infrastructure.
It fixes the documentation too, since the alias only accepts values 0 or
1, not the full range of integers.

We also took the opportunity here to improve the documentation of the
previously converted hung_task_panic (see the patch series [0]) and put
the alias table in alphabetical order.

[0] http://lkml.kernel.org/r/20200427180433.7029-1-vbabka@suse.cz

Signed-off-by: Guilherme G. Piccoli 
Signed-off-by: Andrew Morton 
Acked-by: Vlastimil Babka 
Cc: Kees Cook 
Cc: Iurii Zaikin 
Cc: Luis Chamberlain 
Link: http://lkml.kernel.org/r/20200507214624.21911-1-gpiccoli@canonical.com
Signed-off-by: Linus Torvalds

kernel/hung_task convert hung_task_panic boot parameter to sysctl

2020-06-08T18:05:56+00:00

We can now handle sysctl parameters on kernel command line and have
infrastructure to convert legacy command line options that duplicate
sysctl to become a sysctl alias.

This patch converts the hung_task_panic parameter.  Note that the sysctl
handler is more strict and allows only 0 and 1, while the legacy
parameter allowed any non-zero value.  But there is little reason anyone
would not be using 1.

Signed-off-by: Vlastimil Babka 
Signed-off-by: Andrew Morton 
Reviewed-by: Kees Cook 
Acked-by: Michal Hocko 
Cc: Alexey Dobriyan 
Cc: Christian Brauner 
Cc: David Rientjes 
Cc: "Eric W . Biederman" 
Cc: Greg Kroah-Hartman 
Cc: "Guilherme G . Piccoli" 
Cc: Iurii Zaikin 
Cc: Ivan Teterevkov 
Cc: Luis Chamberlain 
Cc: Masami Hiramatsu 
Cc: Matthew Wilcox 
Cc: Michal Hocko 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/20200427180433.7029-4-vbabka@suse.cz
Signed-off-by: Linus Torvalds