linux-toradex.git/kernel/locking, branch v4.15-rc2

kmemcheck: remove annotations

2017-11-16T02:21:04+00:00

Patch series "kmemcheck: kill kmemcheck", v2.

As discussed at LSF/MM, kill kmemcheck.

KASan is a replacement that is able to work without the limitation of
kmemcheck (single CPU, slow).  KASan is already upstream.

We are also not aware of any users of kmemcheck (or users who don't
consider KASan as a suitable replacement).

The only objection was that since KASAN wasn't supported by all GCC
versions provided by distros at that time we should hold off for 2
years, and try again.

Now that 2 years have passed, and all distros provide gcc that supports
KASAN, kill kmemcheck again for the very same reasons.

This patch (of 4):

Remove kmemcheck annotations, and calls to kmemcheck from the kernel.

[alexander.levin@verizon.com: correctly remove kmemcheck call from dma_map_sg_attrs]
  Link: http://lkml.kernel.org/r/20171012192151.26531-1-alexander.levin@verizon.com
Link: http://lkml.kernel.org/r/20171007030159.22241-2-alexander.levin@verizon.com
Signed-off-by: Sasha Levin 
Cc: Alexander Potapenko 
Cc: Eric W. Biederman 
Cc: Michal Hocko 
Cc: Pekka Enberg 
Cc: Steven Rostedt 
Cc: Tim Hansen 
Cc: Vegard Nossum 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

locking/pvqspinlock: Implement hybrid PV queued/unfair locks

2017-11-08T09:10:04+00:00

Currently, all the lock waiters entering the slowpath will do one
lock stealing attempt to acquire the lock. That helps performance,
especially in VMs with over-committed vCPUs. However, the current
pvqspinlocks still don't perform as good as unfair locks in many cases.
On the other hands, unfair locks do have the problem of lock starvation
that pvqspinlocks don't have.

This patch combines the best attributes of an unfair lock and a
pvqspinlock into a hybrid lock with 2 modes - queued mode & unfair
mode. A lock waiter goes into the unfair mode when there are waiters
in the wait queue but the pending bit isn't set. Otherwise, it will
go into the queued mode waiting in the queue for its turn.

On a 2-socket 36-core E5-2699 v3 system (HT off), a kernel build
(make -j) was done in a VM with unpinned vCPUs 3 times with the
best time selected and  is the number of vCPUs available. The build
times of the original pvqspinlock, hybrid pvqspinlock and unfair lock
with various number of vCPUs are as follows:

  vCPUs    pvqlock     hybrid pvqlock    unfair lock
  -----    -------     --------------    -----------
    30      342.1s         329.1s          329.1s
    36      314.1s         305.3s          307.3s
    45      345.0s         302.1s          306.6s
    54      365.4s         308.6s          307.8s
    72      358.9s         293.6s          303.9s
   108      343.0s         285.9s          304.2s

The hybrid pvqspinlock performs better or comparable to the unfair
lock.

By turning on QUEUED_LOCK_STAT, the table below showed the number
of lock acquisitions in unfair mode and queue mode after a kernel
build with various number of vCPUs.

  vCPUs    queued mode  unfair mode
  -----    -----------  -----------
    30      9,130,518      294,954
    36     10,856,614      386,809
    45      8,467,264   11,475,373
    54      6,409,987   19,670,855
    72      4,782,063   25,712,180

It can be seen that as the VM became more and more over-committed,
the ratio of locks acquired in unfair mode increases. This is all
done automatically to get the best overall performance as possible.

Using a kernel locking microbenchmark with number of locking
threads equals to the number of vCPUs available on the same machine,
the minimum, average and maximum (min/avg/max) numbers of locking
operations done per thread in a 5-second testing interval are shown
below:

  vCPUs         hybrid pvqlock             unfair lock
  -----         --------------             -----------
    36     822,135/881,063/950,363    75,570/313,496/  690,465
    54     542,435/581,664/625,937    35,460/204,280/  457,172
    72     397,500/428,177/499,299    17,933/150,679/  708,001
   108     257,898/288,150/340,871     3,085/181,176/1,257,109

It can be seen that the hybrid pvqspinlocks are more fair and
performant than the unfair locks in this test.

The table below shows the kernel build times on a smaller 2-socket
16-core 32-thread E5-2620 v4 system.

  vCPUs    pvqlock     hybrid pvqlock    unfair lock
  -----    -------     --------------    -----------
    16      436.8s         433.4s          435.6s
    36      366.2s         364.8s          364.5s
    48      423.6s         376.3s          370.2s
    64      433.1s         376.6s          376.8s

Again, the performance of the hybrid pvqspinlock was comparable to
that of the unfair lock.

Signed-off-by: Waiman Long 
Reviewed-by: Juergen Gross 
Reviewed-by: Eduardo Valentin 
Acked-by: Peter Zijlstra 
Cc: Boris Ostrovsky 
Cc: Linus Torvalds 
Cc: Paolo Bonzini 
Cc: Radim Krčmář 
Cc: Thomas Gleixner 
Link: http://lkml.kernel.org/r/1510089486-3466-1-git-send-email-longman@redhat.com
Signed-off-by: Ingo Molnar

locking/rwlocks: Fix comments

2017-11-07T11:22:21+00:00

- fix the list of locking API headers in kernel/locking/spinlock.c
- fix an #endif comment

Signed-off-by: Cheng Jian 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: huawei.libin@huawei.com
Cc: xiexiuqi@huawei.com
Link: http://lkml.kernel.org/r/1509706788-152547-1-git-send-email-cj.chengjian@huawei.com
Signed-off-by: Ingo Molnar

Merge branch 'linus' into locking/core, to resolve conflicts

2017-11-07T09:32:44+00:00

Conflicts:
	include/linux/compiler-clang.h
	include/linux/compiler-gcc.h
	include/linux/compiler-intel.h
	include/uapi/linux/stddef.h

Signed-off-by: Ingo Molnar

License cleanup: add SPDX GPL-2.0 license identifier to files with no license

2017-11-02T10:10:55+00:00

Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.

By default all files without license information are under the default
license of the kernel, which is GPL version 2.

Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier.  The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.

This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.

How this work was done:

Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
 - file had no licensing information it it.
 - file was a */uapi/* one with no licensing information in it,
 - file was a */uapi/* one with existing licensing information,

Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.

The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne.  Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.

The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed.  Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.

Criteria used to select files for SPDX license identifier tagging was:
 - Files considered eligible had to be source code files.
 - Make and config files were included as candidates if they contained >5
   lines of source
 - File already had some variant of a license header in it (even if <5
   lines).

All documentation files were explicitly excluded.

The following heuristics were used to determine which SPDX license
identifiers to apply.

 - when both scanners couldn't find any license traces, file was
   considered to have no license information in it, and the top level
   COPYING file license applied.

   For non */uapi/* files that summary was:

   SPDX license identifier                            # files
   ---------------------------------------------------|-------
   GPL-2.0                                              11139

   and resulted in the first patch in this series.

   If that file was a */uapi/* path one, it was "GPL-2.0 WITH
   Linux-syscall-note" otherwise it was "GPL-2.0".  Results of that was:

   SPDX license identifier                            # files
   ---------------------------------------------------|-------
   GPL-2.0 WITH Linux-syscall-note                        930

   and resulted in the second patch in this series.

 - if a file had some form of licensing information in it, and was one
   of the */uapi/* ones, it was denoted with the Linux-syscall-note if
   any GPL family license was found in the file or had no licensing in
   it (per prior point).  Results summary:

   SPDX license identifier                            # files
   ---------------------------------------------------|------
   GPL-2.0 WITH Linux-syscall-note                       270
   GPL-2.0+ WITH Linux-syscall-note                      169
   ((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause)    21
   ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause)    17
   LGPL-2.1+ WITH Linux-syscall-note                      15
   GPL-1.0+ WITH Linux-syscall-note                       14
   ((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause)    5
   LGPL-2.0+ WITH Linux-syscall-note                       4
   LGPL-2.1 WITH Linux-syscall-note                        3
   ((GPL-2.0 WITH Linux-syscall-note) OR MIT)              3
   ((GPL-2.0 WITH Linux-syscall-note) AND MIT)             1

   and that resulted in the third patch in this series.

 - when the two scanners agreed on the detected license(s), that became
   the concluded license(s).

 - when there was disagreement between the two scanners (one detected a
   license but the other didn't, or they both detected different
   licenses) a manual inspection of the file occurred.

 - In most cases a manual inspection of the information in the file
   resulted in a clear resolution of the license that should apply (and
   which scanner probably needed to revisit its heuristics).

 - When it was not immediately clear, the license identifier was
   confirmed with lawyers working with the Linux Foundation.

 - If there was any question as to the appropriate license identifier,
   the file was flagged for further research and to be revisited later
   in time.

In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.

Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights.  The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.

Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.

In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.

Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
 - a full scancode scan run, collecting the matched texts, detected
   license ids and scores
 - reviewing anything where there was a license detected (about 500+
   files) to ensure that the applied SPDX license was correct
 - reviewing anything where there was no detection but the patch license
   was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
   SPDX license was correct

This produced a worksheet with 20 files needing minor correction.  This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.

These .csv files were then reviewed by Greg.  Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected.  This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.)  Finally Greg ran the script using the .csv files to
generate the patches.

Reviewed-by: Kate Stewart 
Reviewed-by: Philippe Ombredanne 
Reviewed-by: Thomas Gleixner 
Signed-off-by: Greg Kroah-Hartman

locking/lockdep: Introduce CONFIG_BOOTPARAM_LOCKDEP_CROSSRELEASE_FULLSTACK=y

2017-10-25T10:19:02+00:00

Add a Kconfig knob that enables the lockdep "crossrelease_fullstack" boot parameter.

Suggested-by: Ingo Molnar 
Signed-off-by: Byungchul Park 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: amir73il@gmail.com
Cc: axboe@kernel.dk
Cc: darrick.wong@oracle.com
Cc: david@fromorbit.com
Cc: hch@infradead.org
Cc: idryomov@gmail.com
Cc: johan@kernel.org
Cc: johannes.berg@intel.com
Cc: kernel-team@lge.com
Cc: linux-block@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-xfs@vger.kernel.org
Cc: oleg@redhat.com
Cc: tj@kernel.org
Link: http://lkml.kernel.org/r/1508921765-15396-7-git-send-email-byungchul.park@lge.com
Signed-off-by: Ingo Molnar

locking/lockdep: Add a boot parameter allowing unwind in cross-release and disable it by default

2017-10-25T10:19:01+00:00

Johan Hovold reported a heavy performance regression caused by lockdep
cross-release:

 > Boot time (from "Linux version" to login prompt) had in fact doubled
 > since 4.13 where it took 17 seconds (with my current config) compared to
 > the 35 seconds I now see with 4.14-rc4.
 >
 > I quick bisect pointed to lockdep and specifically the following commit:
 >
 >	28a903f63ec0 ("locking/lockdep: Handle non(or multi)-acquisition
 >	               of a crosslock")
 >
 > which I've verified is the commit which doubled the boot time (compared
 > to 28a903f63ec0^) (added by lockdep crossrelease series [1]).

Currently cross-release performs unwind on every acquisition, but that
is very expensive.

This patch makes unwind optional and disables it by default and only
records acquire_ip.

Full stack traces are sometimes required for full analysis, in which
case a boot paramter, crossrelease_fullstack, can be specified.

On my qemu Ubuntu machine (x86_64, 4 cores, 512M), the regression was
fixed. We measure boot times with 'perf stat --null --repeat 10 $QEMU',
where $QEMU launches a kernel with init=/bin/true:

1. No lockdep enabled:

 Performance counter stats for 'qemu_booting_time.sh bzImage' (10 runs):

       2.756558155 seconds time elapsed                    ( +-  0.09% )

2. Lockdep enabled:

 Performance counter stats for 'qemu_booting_time.sh bzImage' (10 runs):

       2.968710420 seconds time elapsed                    ( +-  0.12% )

3. Lockdep enabled + cross-release enabled:

 Performance counter stats for 'qemu_booting_time.sh bzImage' (10 runs):

       3.153839636 seconds time elapsed                    ( +-  0.31% )

4. Lockdep enabled + cross-release enabled + this patch applied:

 Performance counter stats for 'qemu_booting_time.sh bzImage' (10 runs):

       2.963669551 seconds time elapsed                    ( +-  0.11% )

I.e. lockdep cross-release performance is now indistinguishable from
vanilla lockdep.

Bisected-by: Johan Hovold 
Analyzed-by: Thomas Gleixner 
Suggested-by: Thomas Gleixner 
Reported-by: Johan Hovold 
Signed-off-by: Byungchul Park 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: amir73il@gmail.com
Cc: axboe@kernel.dk
Cc: darrick.wong@oracle.com
Cc: david@fromorbit.com
Cc: hch@infradead.org
Cc: idryomov@gmail.com
Cc: johannes.berg@intel.com
Cc: kernel-team@lge.com
Cc: linux-block@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-mm@kvack.org
Cc: linux-xfs@vger.kernel.org
Cc: oleg@redhat.com
Cc: tj@kernel.org
Link: http://lkml.kernel.org/r/1508921765-15396-5-git-send-email-byungchul.park@lge.com
Signed-off-by: Ingo Molnar

locking/qrwlock: Prevent slowpath writers getting held up by fastpath

2017-10-25T08:57:25+00:00

When a prospective writer takes the qrwlock locking slowpath due to the
lock being held, it attempts to cmpxchg the wmode field from 0 to
_QW_WAITING so that concurrent lockers also take the slowpath and queue
on the spinlock accordingly, allowing the lockers to drain.

Unfortunately, this isn't fair, because a fastpath writer that comes in
after the lock is made available but before the _QW_WAITING flag is set
can effectively jump the queue. If there is a steady stream of prospective
writers, then the waiter will be held off indefinitely.

This patch restores fairness by separating _QW_WAITING and _QW_LOCKED
into two distinct fields: _QW_LOCKED continues to occupy the bottom byte
of the lockword so that it can be cleared unconditionally when unlocking,
but _QW_WAITING now occupies what used to be the bottom bit of the reader
count. This then forces the slow-path for concurrent lockers.

Tested-by: Waiman Long 
Tested-by: Jeremy Linton 
Tested-by: Adam Wallis 
Tested-by: Jan Glauber 
Signed-off-by: Will Deacon 
Acked-by: Peter Zijlstra 
Cc: Boqun Feng 
Cc: Jeremy.Linton@arm.com
Cc: Linus Torvalds 
Cc: Paul E. McKenney 
Cc: Thomas Gleixner 
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1507810851-306-6-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar

locking/qrwlock: Use atomic_cond_read_acquire() when spinning in qrwlock

2017-10-25T08:57:24+00:00

The qrwlock slowpaths involve spinning when either a prospective reader
is waiting for a concurrent writer to drain, or a prospective writer is
waiting for concurrent readers to drain. In both of these situations,
atomic_cond_read_acquire() can be used to avoid busy-waiting and make use
of any backoff functionality provided by the architecture.

This patch replaces the open-code loops and rspin_until_writer_unlock()
implementation with atomic_cond_read_acquire(). The write mode transition
zero to _QW_WAITING is left alone, since (a) this doesn't need acquire
semantics and (b) should be fast.

Tested-by: Waiman Long 
Tested-by: Jeremy Linton 
Tested-by: Adam Wallis 
Tested-by: Jan Glauber 
Signed-off-by: Will Deacon 
Acked-by: Peter Zijlstra 
Cc: Boqun Feng 
Cc: Jeremy.Linton@arm.com
Cc: Linus Torvalds 
Cc: Paul E. McKenney 
Cc: Thomas Gleixner 
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1507810851-306-4-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar

locking/qrwlock: Use 'struct qrwlock' instead of 'struct __qrwlock'

2017-10-25T08:57:24+00:00

There's no good reason to keep the internal structure of struct qrwlock
hidden from qrwlock.h, particularly as it's actually needed for unlock
and ends up being abstracted independently behind the __qrwlock_write_byte()
function.

Stop pretending we can hide this stuff, and move the __qrwlock definition
into qrwlock, removing the __qrwlock_write_byte() nastiness and using the
same struct definition everywhere instead.

Signed-off-by: Will Deacon 
Acked-by: Peter Zijlstra 
Cc: Boqun Feng 
Cc: Jeremy.Linton@arm.com
Cc: Linus Torvalds 
Cc: Paul E. McKenney 
Cc: Thomas Gleixner 
Cc: Waiman Long 
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1507810851-306-2-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar