Merge branches 'doc.2020.06.29a', 'fixes.2020.06.29a', 'kfree_rcu.2020.06.29a', 'rcu-tasks.2020.06.29a', 'scale.2020.06.29a', 'srcu.2020.06.29a' and 'torture.2020.06.29a' into HEAD

doc.2020.06.29a:  Documentation updates.
fixes.2020.06.29a:  Miscellaneous fixes.
kfree_rcu.2020.06.29a:  kfree_rcu() updates.
rcu-tasks.2020.06.29a:  RCU Tasks updates.
scale.2020.06.29a:  Read-side scalability tests.
srcu.2020.06.29a:  SRCU updates.
torture.2020.06.29a:  Torture-test updates.

In the dim distant past, qemu commands needed to be run from the
rcutorture directory, but this is no longer the case.  This commit
therefore removes the now-useless "cd $KVM" from the kvm-test-1-run.sh
script.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Currently, the qemu command is constructed twice, once to dump it
to the qemu-cmd file and again to execute it.  This is of course an
accident waiting to happen, but is done to ensure that the remainder
of the script has an accurate idea of the running qemu command's PID.
This commit therefore places both the qemu command and the PID capture
into a new temporary file and sources that temporary file.  Thus the
single construction of the qemu command into the qemu-cmd file suffices
for both purposes.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

If there is a large number of torture tests running concurrently,
all of which are dumping large ftrace buffers at shutdown time, the
resulting dumping can take a very long time, particularly on systems
with rotating-rust storage.  This commit therefore adds a default-off
torture.ftrace_dump_at_shutdown module parameter that enables
shutdown-time ftrace-buffer dumping.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit adds a script that transforms qemu-cmd files to allow them
and the corresponding kernels to be run in contexts other than the one
that they were created for, including on systems other than the one that
they were built on.  For example, this allows the build products from a
--buildonly run to be transformed to allow distributed rcutorture testing.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit adds a few more hints about how to use tracing as comments
at the end of kvm.sh.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Using --kcsan when the compiler does not support KCSAN results in this:

:CONFIG_KCSAN=y: improperly set
:CONFIG_KCSAN_REPORT_ONCE_IN_MS=100000: improperly set
:CONFIG_KCSAN_VERBOSE=y: improperly set
:CONFIG_KCSAN_INTERRUPT_WATCHER=y: improperly set
Clean KCSAN run in /home/git/linux-rcu/tools/testing/selftests/rcutorture/res/2020.06.16-09.53.16

This is a bit obtuse, so this commit adds checks resulting in this:

:CONFIG_KCSAN=y: improperly set
:CONFIG_KCSAN_REPORT_ONCE_IN_MS=100000: improperly set
:CONFIG_KCSAN_VERBOSE=y: improperly set
:CONFIG_KCSAN_INTERRUPT_WATCHER=y: improperly set
Compiler or architecture does not support KCSAN!
Did you forget to switch your compiler with --kmake-arg CC=<cc-that-supports-kcsan>?
Suggested-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Marco Elver <elver@google.com>

Currently, kvm-recheck.sh complains that qemu failed for --buildonly
runs, which is sort of true given that qemu can hardly succeed if not
invoked in the first place.  Nevertheless, this commit swaps the order
of checks in kvm-recheck.sh so that --buildonly runs will be summarized
more straightforwardly.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

We need to pass the arguments provided to --kmake-arg to all make
invocations. In particular, the make invocations generating the configs
need to see the final make arguments, e.g. if config variables depend on
particular variables that are passed to make.

For example, when using '--kcsan --kmake-arg CC=clang-11', we would lose
CONFIG_KCSAN=y due to 'make oldconfig' not seeing that we want to use a
compiler that supports KCSAN.
Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

RCU is supposed to be watching all non-idle kernel code and also all
softirq handlers.  This commit adds some teeth to this statement by
adding a WARN_ON_ONCE().
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit pulls the simple pattern-based error detection from the
console log into a new console-badness.sh file.  This will enable future
commits to end a run on the first error.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

When bisecting RCU issues, it is often the case that the first error in
an unsuccessful run will happen quickly, but that a successful run must
go on for some time in order to obtain a sufficiently low false-negative
error rate.  In many cases, a bisection requires multiple concurrent
runs, in which case the first failure in any run indicates failure,
pure and simple.  In such cases, it would speed things up greatly if
the first failure terminated all runs.

This commit therefore adds scripting that checks for a file named "STOP"
in the top-level results directory, terminating the run when it appears.
Note that in-progress builds will continue until completion, but future
builds and all runs will be cut short.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

One reason to do a --buildonly run is to use the build products elsewhere,
for example, to do the actual test on some other system.  Part of doing
the test is the actual qemu command, which is not currently produced
by --buildonly runs.  This commit therefore causes --buildonly runs to
create this file.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Coccinelle reports a warning

WARNING: Assignment of 0/1 to bool variable

The root cause is that the variable lastphase is a bool, but is
initialised with integer 0.  This commit therefore replaces the 0 with
a false.
Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Leaving off the kvm.sh script's --cpus argument results in the script
testing the scenarios sequentially, which can be quite slow.  However,
having to specify the actual number of CPUs can be error-prone.
This commit therefore adds a --allcpus argument that causes kvm.sh to
use all available CPUs.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

The identify_qemu_vcpus bash function can return numbers including
whitespace characters, which can be a bit annoying in some bash
dollar-sign substitutions.  This commit therefore strips all spaces and
tabs from the value that identify_qemu_vcpus outputs.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Currently, the rcu_torture_current variable remains non-NULL until after
all readers have stopped.  During this time, rcu_torture_stats_print()
will think that the test is still ongoing, which can result in confusing
dmesg output.  This commit therefore NULLs rcu_torture_current immediately
after the rcu_torture_writer() kthread has decided to stop, thus informing
rcu_torture_stats_print() much sooner.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

The current console parsing assumes that console lines containing "!!!"
are statistics lines from which it can parse the number of rcutorture
too-short grace-period failures.  This prints confusing output for
other problems, including memory exhaustion.  This commit therefore
differentiates between these cases and prints an appropriate error string.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

The torture-test recheck logic fails to set the configfile variable to
the current scenario, so this commit properly initializes this variable.
This change isn't critical given that all errors for a given scenario
follow that scenario's heading, but it is easier on the eyes to repeat it.
And this repetition also prevents confusion as to whether a given message
goes with the previous heading or the next one.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Several variants of Linux-kernel RCU interact with task-exit processing,
including preemptible RCU, Tasks RCU, and Tasks Trace RCU.  This commit
therefore adds testing of this interaction to rcutorture by adding
rcutorture.read_exit_burst and rcutorture.read_exit_delay kernel-boot
parameters.  These kernel parameters control the frequency and spacing
of special read-then-exit kthreads that are spawned.

[ paulmck: Apply feedback from Dan Carpenter's static checker. ]
[ paulmck: Reduce latency to avoid false-positive shutdown hangs. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit fixes the following coccicheck warnings:

kernel/locking/locktorture.c:689:6-10: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:907:2-20: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:938:3-20: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:668:2-19: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:674:2-19: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:634:2-20: WARNING: Assignment of 0/1 to bool variable
kernel/locking/locktorture.c:640:2-20: WARNING: Assignment of 0/1 to bool variable
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit adds a kvm-check-branches.sh script that takes a list
of commits and commit ranges and runs a short rcutorture test on all
scenarios on each specified commit.  A summary is printed at the end, and
the script returns success if all rcutorture runs completed without error.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

On some (probably misconfigured) systems, the torture-test scripting
will cause qemu to complain about missing EFI firmware, often because
qemu is trying to traverse broken symbolic links to find that firmware.
Which is a bit silly given that the default torture-test guest OS has
but a single binary for its userspace, and thus is unlikely to do much
in the way of networking in any case.

This commit therefore avoids such problems by specifying "-net none"
to qemu unless the TORTURE_QEMU_INTERACTIVE environment variable is set
(for example, by having specified "--interactive" to kvm.sh), in which
case "-net nic -net user" is specified to qemu instead.  Either choice
may be overridden by specifying the "-net" argument of your choice to
the kvm.sh "--qemu-args" parameter.

Link: https://lore.kernel.org/lkml/20190701141403.GA246562@google.comReported-by: Joel Fernandes <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

SRCU disables interrupts to get a stable per-CPU pointer and then
acquires the spinlock which is in the per-CPU data structure. The
release uses spin_unlock_irqrestore(). While this is correct on a non-RT
kernel, this conflicts with the RT semantics because the spinlock is
converted to a 'sleeping' spinlock. Sleeping locks can obviously not be
acquired with interrupts disabled.

Acquire the per-CPU pointer `ssp->sda' without disabling preemption and
then acquire the spinlock_t of the per-CPU data structure. The lock will
ensure that the data is consistent.

The added call to check_init_srcu_struct() is now needed because a
statically defined srcu_struct may remain uninitialized until this
point and the newly introduced locking operation requires an initialized
spinlock_t.

This change was tested for four hours with 8*SRCU-N and 8*SRCU-P without
causing any warnings.

Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: rcu@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit fixes a typo in a comment.
Signed-off-by: Ethon Paul <ethp@qq.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit renames the rcutorture config/refperf to config/refscale to
further avoid conflation with the Linux kernel's perf feature.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit further avoids conflation of refperf with the kernel's perf
feature by renaming kernel/rcu/refperf.c to kernel/rcu/refscale.c,
and also by similarly renaming the functions and variables inside
this file.  This has the side effect of changing the names of the
kernel boot parameters, so kernel-parameters.txt and ver_functions.sh
are also updated.

The rcutorture --torture type remains refperf, and this will be
addressed in a separate commit.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

The old Kconfig option name is all too easy to conflate with the
unrelated "perf" feature, so this commit renames RCU_REF_PERF_TEST to
RCU_REF_SCALE_TEST.
Reported-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

The synchronize_rcu_tasks_trace() header comment incorrectly claims that
any number of things delimit RCU Tasks Trace read-side critical sections,
when in fact only rcu_read_lock_trace() and rcu_read_unlock_trace() do so.
This commit therefore fixes this comment, and, while in the area, fixes
a typo in the rcu_read_lock_trace() header comment.
Reported-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit adds testing for RCU Tasks readers to the refperf module.
This also applies to RCU Rude readers, as both flavors have empty
(as in non-existent) read-side markers.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit adds testing for RCU Tasks Trace readers to the refperf module.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

The current units of microseconds are too coarse, so this commit
changes the units to nanoseconds.  However, ndelay is used only for the
nanoseconds with udelay being used for whole microseconds.  For example,
setting refperf.readdelay=1500 results in a udelay(1) followed by an
ndelay(500).
Suggested-by: Akira Yokosawa <akiyks@gmail.com>
[ paulmck: Abstracted delay per Akira feedback and move from 80 to 100 lines. ]
[ paulmck: Fix names as suggested by kbuild test robot. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

A 64-bit division was introduced in refperf, breaking compilation
on all 32-bit architectures:

kernel/rcu/refperf.o: in function `main_func':
refperf.c:(.text+0x57c): undefined reference to `__aeabi_uldivmod'

Fix this by using div_u64 to mark the expensive operation.

[ paulmck: Update primitive and format per Nathan Chancellor. ]
Fixes: bd5b16d6c88d ("refperf: Allow decimal nanoseconds")
Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: Valdis Klētnieks <valdis.kletnieks@vt.edu>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit adds documentation for the rcuperf module parameters.

Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

With the various measurement optimizations, 10,000 loops normally
suffices.  This commit therefore reduces the refperf.loops default value
from 10,000,000 to 10,000.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit adds a refperf.readdelay module parameter that controls the
duration of each critical section.  This parameter allows gathering data
showing how the performance differences between the various primitives
vary with critical-section length.

Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit moves the reader-launch wait loop from ref_perf_init()
to main_func(), removing one layer of wakeup and allowing slightly
faster system boot.

Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Currently, it is necessary to manually edit the console output to see
anything more than statistics, and sometimes the statistics can indicate
outliers that need more investigation.  This commit therefore dumps out
the per-experiment measurements, sorted in ascending order, just before
dumping out the statistics.

Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

The experiment-number column is currently labeled "Threads", which is
misleading at best.  This commit therefore relabels it as "Runs", and
adjusts the scripts accordingly.

Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit causes all the readers to start running unmeasured load
until all readers have done at least one such run (thus having warmed
up), then run the measured load, and then run unmeasured load until all
readers have completed their measured load.  This approach avoids any
thread running measured load while other readers are idle.

Cc: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>