linux-stable.git/Documentation, branch v5.3.9

sched/fair: Fix low cpu usage with high throttling by removing expiration of cpu-local slices

2019-11-06T12:09:31+00:00

commit de53fd7aedb100f03e5d2231cfce0e4993282425 upstream.

It has been observed, that highly-threaded, non-cpu-bound applications
running under cpu.cfs_quota_us constraints can hit a high percentage of
periods throttled while simultaneously not consuming the allocated
amount of quota. This use case is typical of user-interactive non-cpu
bound applications, such as those running in kubernetes or mesos when
run on multiple cpu cores.

This has been root caused to cpu-local run queue being allocated per cpu
bandwidth slices, and then not fully using that slice within the period.
At which point the slice and quota expires. This expiration of unused
slice results in applications not being able to utilize the quota for
which they are allocated.

The non-expiration of per-cpu slices was recently fixed by
'commit 512ac999d275 ("sched/fair: Fix bandwidth timer clock drift
condition")'. Prior to that it appears that this had been broken since
at least 'commit 51f2176d74ac ("sched/fair: Fix unlocked reads of some
cfs_b->quota/period")' which was introduced in v3.16-rc1 in 2014. That
added the following conditional which resulted in slices never being
expired.

if (cfs_rq->runtime_expires != cfs_b->runtime_expires) {
	/* extend local deadline, drift is bounded above by 2 ticks */
	cfs_rq->runtime_expires += TICK_NSEC;

Because this was broken for nearly 5 years, and has recently been fixed
and is now being noticed by many users running kubernetes
(https://github.com/kubernetes/kubernetes/issues/67577) it is my opinion
that the mechanisms around expiring runtime should be removed
altogether.

This allows quota already allocated to per-cpu run-queues to live longer
than the period boundary. This allows threads on runqueues that do not
use much CPU to continue to use their remaining slice over a longer
period of time than cpu.cfs_period_us. However, this helps prevent the
above condition of hitting throttling while also not fully utilizing
your cpu quota.

This theoretically allows a machine to use slightly more than its
allotted quota in some periods. This overflow would be bounded by the
remaining quota left on each per-cpu runqueueu. This is typically no
more than min_cfs_rq_runtime=1ms per cpu. For CPU bound tasks this will
change nothing, as they should theoretically fully utilize all of their
quota in each period. For user-interactive tasks as described above this
provides a much better user/application experience as their cpu
utilization will more closely match the amount they requested when they
hit throttling. This means that cpu limits no longer strictly apply per
period for non-cpu bound applications, but that they are still accurate
over longer timeframes.

This greatly improves performance of high-thread-count, non-cpu bound
applications with low cfs_quota_us allocation on high-core-count
machines. In the case of an artificial testcase (10ms/100ms of quota on
80 CPU machine), this commit resulted in almost 30x performance
improvement, while still maintaining correct cpu quota restrictions.
That testcase is available at https://github.com/indeedeng/fibtest.

Fixes: 512ac999d275 ("sched/fair: Fix bandwidth timer clock drift condition")
Signed-off-by: Dave Chiluk 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Phil Auld 
Reviewed-by: Ben Segall 
Cc: Ingo Molnar 
Cc: John Hammond 
Cc: Jonathan Corbet 
Cc: Kyle Anderson 
Cc: Gabriel Munos 
Cc: Peter Oskolkov 
Cc: Cong Wang 
Cc: Brendan Gregg 
Link: https://lkml.kernel.org/r/1563900266-19734-2-git-send-email-chiluk+linux@indeed.com
Signed-off-by: Greg Kroah-Hartman

x86/xen: Return from panic notifier

2019-11-06T12:08:26+00:00

[ Upstream commit c6875f3aacf2a5a913205accddabf0bfb75cac76 ]

Currently execution of panic() continues until Xen's panic notifier
(xen_panic_event()) is called at which point we make a hypercall that
never returns.

This means that any notifier that is supposed to be called later as
well as significant part of panic() code (such as pstore writes from
kmsg_dump()) is never executed.

There is no reason for xen_panic_event() to be this last point in
execution since panic()'s emergency_restart() will call into
xen_emergency_restart() from where we can perform our hypercall.

Nevertheless, we will provide xen_legacy_crash boot option that will
preserve original behavior during crash. This option could be used,
for example, if running kernel dumper (which happens after panic
notifiers) is undesirable.

Reported-by: James Dingwall 
Signed-off-by: Boris Ostrovsky 
Reviewed-by: Juergen Gross 
Signed-off-by: Sasha Levin

arm64: Allow CAVIUM_TX2_ERRATUM_219 to be selected

2019-10-29T08:22:38+00:00

commit 603afdc9438ac546181e843f807253d75d3dbc45 upstream.

Allow the user to select the workaround for TX2-219, and update
the silicon-errata.rst file to reflect this.

Cc: 
Signed-off-by: Marc Zyngier 
Signed-off-by: Will Deacon 
Signed-off-by: Greg Kroah-Hartman

USB: rio500: Remove Rio 500 kernel driver

2019-10-17T20:46:30+00:00

commit 015664d15270a112c2371d812f03f7c579b35a73 upstream.

The Rio500 kernel driver has not been used by Rio500 owners since 2001
not long after the rio500 project added support for a user-space USB stack
through the very first versions of usbdevfs and then libusb.

Support for the kernel driver was removed from the upstream utilities
in 2008:
https://gitlab.freedesktop.org/hadess/rio500/commit/943f624ab721eb8281c287650fcc9e2026f6f5db

Cc: Cesar Miquel 
Signed-off-by: Bastien Nocera 
Cc: stable 
Link: https://lore.kernel.org/r/6251c17584d220472ce882a3d9c199c401a51a71.camel@hadess.net
Signed-off-by: Greg Kroah-Hartman

ALSA: hda - Add a quirk model for fixing Huawei Matebook X right speaker

2019-10-05T13:12:09+00:00

[ Upstream commit a2ef03fe617a8365fb7794531b11ba587509a9b9 ]

[ This is rather a revival of the patch Tomas sent in months ago, but
  applying only with the quirk model option -- tiwai ]

Hard coded coefficients to make Huawuei Matebook X right speaker
work. The Matebook X has a ALC298, please refer to bug 197801 on
how these numbers were reverse engineered from the Windows driver

The reversed engineered sequence represents a repeating pattern
of verbs, and the only values that are changing periodically are
written on indexes 0x23 and 0x25:

0x500, 0x23
0x400, VALUE1
0x500, 0x25
0x400, VALUE2

* skipped reading sequences (0x500 - 0xc00 sequences are ignored)
* static values from reverse engineering are used

NOTE: since a significant risk is still considered, this is provided
as an experimental fix that isn't applied as default for now.  For
enabling the fix, you'll have to choose huawei-mbx-stereo via model
option of snd-hda-intel module.

If we get feedback from users that this works stably, we may apply it
per default.

[ Some coding style fixes and replacement with AC_VERB_* by tiwai ]

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=197801
Signed-off-by: Tomas Espeleta 
Signed-off-by: Takashi Iwai 
Signed-off-by: Sasha Levin

ASoC: dt-bindings: sun4i-spdif: Fix dma-names warning

2019-10-05T13:12:02+00:00

[ Upstream commit 1a8e7cdfa4f5872bf0c202d09bff6628aba6b9f6 ]

Even though the H6 compatible has been properly added, the exeption for the
number of DMA channels hasn't been updated, leading in a validation
warning.

Fix this.

Fixes: b20453031472 ("dt-bindings: sound: sun4i-spdif: Add Allwinner H6 compatible")
Signed-off-by: Maxime Ripard 
Link: https://lore.kernel.org/r/20190828125209.28173-1-mripard@kernel.org
Reviewed-by: Rob Herring 
Signed-off-by: Mark Brown 
Signed-off-by: Sasha Levin

ovl: fix regression caused by overlapping layers detection

2019-09-21T05:19:45+00:00

commit 0be0bfd2de9dfdd2098a9c5b14bdd8f739c9165d upstream.

Once upon a time, commit 2cac0c00a6cd ("ovl: get exclusive ownership on
upper/work dirs") in v4.13 added some sanity checks on overlayfs layers.
This change caused a docker regression. The root cause was mount leaks
by docker, which as far as I know, still exist.

To mitigate the regression, commit 85fdee1eef1a ("ovl: fix regression
caused by exclusive upper/work dir protection") in v4.14 turned the
mount errors into warnings for the default index=off configuration.

Recently, commit 146d62e5a586 ("ovl: detect overlapping layers") in
v5.2, re-introduced exclusive upper/work dir checks regardless of
index=off configuration.

This changes the status quo and mount leak related bug reports have
started to re-surface. Restore the status quo to fix the regressions.
To clarify, index=off does NOT relax overlapping layers check for this
ovelayfs mount. index=off only relaxes exclusive upper/work dir checks
with another overlayfs mount.

To cover the part of overlapping layers detection that used the
exclusive upper/work dir checks to detect overlap with self upper/work
dir, add a trap also on the work base dir.

Link: https://github.com/moby/moby/issues/34672
Link: https://lore.kernel.org/linux-fsdevel/20171006121405.GA32700@veci.piliscsaba.szeredi.hu/
Link: https://github.com/containers/libpod/issues/3540
Fixes: 146d62e5a586 ("ovl: detect overlapping layers")
Cc:  # v4.19+
Signed-off-by: Amir Goldstein 
Tested-by: Colin Walters 
Signed-off-by: Miklos Szeredi 
Signed-off-by: Greg Kroah-Hartman

Documentation: sphinx: Add missing comma to list of strings

2019-09-21T05:19:42+00:00

commit 11fec009d97e5bd2329ef7d52d71e9f6763f1048 upstream.

In Python, like in C, when a comma is omitted in a list of strings, the
two strings around the missing comma are concatenated.

Cc: stable@vger.kernel.org  # v5.2 only
Signed-off-by: Jonathan Neuschäfer 
Reviewed-by: Mauro Carvalho Chehab 
Signed-off-by: Jonathan Corbet 
Signed-off-by: Greg Kroah-Hartman

riscv: modify the Image header to improve compatibility with the ARM64 header

2019-09-14T02:03:52+00:00

Part of the intention during the definition of the RISC-V kernel image
header was to lay the groundwork for a future merge with the ARM64
image header.  One error during my original review was not noticing
that the RISC-V header's "magic" field was at a different size and
position than the ARM64's "magic" field.  If the existing ARM64 Image
header parsing code were to attempt to parse an existing RISC-V kernel
image header format, it would see a magic number 0.  This is
undesirable, since it's our intention to align as closely as possible
with the ARM64 header format.  Another problem was that the original
"res3" field was not being initialized correctly to zero.

Address these issues by creating a 32-bit "magic2" field in the RISC-V
header which matches the ARM64 "magic" field.  RISC-V binaries will
store "RSC\x05" in this field.  The intention is that the use of the
existing 64-bit "magic" field in the RISC-V header will be deprecated
over time.  Increment the minor version number of the file format to
indicate this change, and update the documentation accordingly.  Fix
the assembler directives in head.S to ensure that reserved fields are
properly zero-initialized.

Signed-off-by: Paul Walmsley 
Reported-by: Palmer Dabbelt 
Reviewed-by: Palmer Dabbelt 
Cc: Atish Patra 
Cc: Karsten Merker 
Link: https://lore.kernel.org/linux-riscv/194c2f10c9806720623430dbf0cc59a965e50448.camel@wdc.com/T/#u
Link: https://lore.kernel.org/linux-riscv/mhng-755b14c4-8f35-4079-a7ff-e421fd1b02bc@palmer-si-x1e/T/#t

Documentation/process: Add Qualcomm process ambassador for hardware security issues

2019-09-07T17:30:54+00:00

Add Trilok Soni as process ambassador for hardware security issues
from Qualcomm.

Signed-off-by: Trilok Soni 
Link: https://lore.kernel.org/r/1567796517-8964-1-git-send-email-tsoni@codeaurora.org
Signed-off-by: Greg Kroah-Hartman