stall.2023.01.09a: RCU CPU stall-warning updates.

doc.2023.01.05a: Documentation update.
fixes.2023.01.23a: Miscellaneous fixes.
kvfree.2023.01.03a: kvfree_rcu() updates.
srcu.2023.01.03a: SRCU updates.
srcu-always.2023.02.02a: Finish making SRCU be unconditionally available.
tasks.2023.01.03a: Tasks-RCU updates.
torture.2023.01.05a: Torture-test updates.
torturescript.2023.01.03a: Torture-test scripting updates.

Boot and suspend/resume should not be slowed down in kernels built with
CONFIG_RCU_LAZY=y.  In particular, suspend can sometimes fail in such
kernels.

This commit therefore adds rcu_async_hurry(), rcu_async_relax(), and
rcu_async_should_hurry() functions that track whether or not either
a boot or a suspend/resume operation is in progress.  This will
enable a later commit to refrain from laziness during those times.

Export rcu_async_should_hurry(), rcu_async_hurry(), and rcu_async_relax()
for later use by rcutorture.

[ paulmck: Apply feedback from Steve Rostedt. ]

Fixes: 3cb278e73be5 ("rcu: Make call_rcu() lazy to save power")
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Because RCU CPU stall warnings are driven from the scheduling-clock
interrupt handler, a workload consisting of a very large number of
short-duration hardware interrupts can result in misleading stall-warning
messages.  On systems supporting only a single level of interrupts,
that is, where interrupts handlers cannot be interrupted, this can
produce misleading diagnostics.  The stack traces will show the
innocent-bystander interrupted task, not the interrupts that are
at the very least exacerbating the stall.

This situation can be improved by displaying the number of interrupts
and the CPU time that they have consumed.  Diagnosing other types
of stalls can be eased by also providing the count of softirqs and
the CPU time that they consumed as well as the number of context
switches and the task-level CPU time consumed.

Consider the following output given this change:

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu:     0-....: (1250 ticks this GP) <omitted>
rcu:          hardirqs   softirqs   csw/system
rcu:  number:      624         45            0
rcu: cputime:       69          1         2425   ==> 2500(ms)

This output shows that the number of hard and soft interrupts is small,
there are no context switches, and the system takes up a lot of time. This
indicates that the current task is looping with preemption disabled.

The impact on system performance is negligible because snapshot is
recorded only once for all continuous RCU stalls.

This added debugging information is suppressed by default and can be
enabled by building the kernel with CONFIG_RCU_CPU_STALL_CPUTIME=y or
by booting with rcupdate.rcu_cpu_stall_cputime=1.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Mukesh Ojha <quic_mojha@quicinc.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit adds trivial test code for srcu_down_read() and
srcu_up_read().

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Kernels built with the CONFIG_TREE_SRCU Kconfig option set and then
booted with rcupdate.rcu_self_test=1 and srcutree.convert_to_big=1 will
test Tree SRCU during early boot.  The early_srcu structure's srcu_node
array will be allocated when init_srcu_struct_fields() is invoked,
but after the test completes this early_srcu structure will not be used.

This commit therefore invokes cleanup_srcu_struct() to free that srcu_node
structure.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit introduces the rcupdate.rcu_exp_stall_task_details kernel
boot parameter, which cause expedited RCU CPU stall warnings to dump
the stacks of any tasks blocking the current expedited grace period.

Reported-by: David Howells <dhowells@redhat.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

This commit tests synchronize_rcu() and synchronize_rcu_expedited()
at the end of rcu_init(), in addition to the test already at the
beginning of that function.  These tests are run only in kernels built
with CONFIG_PROVE_RCU=y.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Kernels configured with CONFIG_PRINTK=n and CONFIG_SRCU=n get build
failures.  This causes trouble for deep embedded systems.  But given
that there are more than 25 instances of "select SRCU" in the kernel,
it is hard to believe that there are many kernels running in production
without SRCU.  This commit therefore makes SRCU mandatory.  The SRCU
Kconfig option remains for backwards compatibility, and will be removed
when it is no longer used.

[ paulmck: Update per kernel test robot feedback. ]

Reported-by: John Ogness <john.ogness@linutronix.de>
Reported-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: <linux-arch@vger.kernel.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested
Reviewed-by: John Ogness <john.ogness@linutronix.de>

ctxt.2022.07.05a: Linux-kernel memory model development branch.