Pull RCU fix from Paul McKenney:
 "This is a fix for a regression in the v5.10 merge window, but it was
  reported quite late in the v5.10 process, plus generating and testing
  the fix took some time.

  The regression is due to commit 36dadef23fcc ("kprobes: Init kprobes
  in early_initcall") which on powerpc can use RCU Tasks before
  initialization, resulting in boot failures.

  The fix is straightforward, simply moving initialization of RCU Tasks
  before the early_initcall()s. The fix has been exposed to -next and
  kbuild test robot testing, and has been tested by the PowerPC guys"

* 'rcu/urgent' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu:
  rcu-tasks: Move RCU-tasks initialization to before early_initcall()

Pull scheduler updates from Thomas Gleixner:

 - migrate_disable/enable() support which originates from the RT tree
   and is now a prerequisite for the new preemptible kmap_local() API
   which aims to replace kmap_atomic().

 - A fair amount of topology and NUMA related improvements

 - Improvements for the frequency invariant calculations

 - Enhanced robustness for the global CPU priority tracking and decision
   making

 - The usual small fixes and enhancements all over the place

* tag 'sched-core-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (61 commits)
  sched/fair: Trivial correction of the newidle_balance() comment
  sched/fair: Clear SMT siblings after determining the core is not idle
  sched: Fix kernel-doc markup
  x86: Print ratio freq_max/freq_base used in frequency invariance calculations
  x86, sched: Use midpoint of max_boost and max_P for frequency invariance on AMD EPYC
  x86, sched: Calculate frequency invariance for AMD systems
  irq_work: Optimize irq_work_single()
  smp: Cleanup smp_call_function*()
  irq_work: Cleanup
  sched: Limit the amount of NUMA imbalance that can exist at fork time
  sched/numa: Allow a floating imbalance between NUMA nodes
  sched: Avoid unnecessary calculation of load imbalance at clone time
  sched/numa: Rename nr_running and break out the magic number
  sched: Make migrate_disable/enable() independent of RT
  sched/topology: Condition EAS enablement on FIE support
  arm64: Rebuild sched domains on invariance status changes
  sched/topology,schedutil: Wrap sched domains rebuild
  sched/uclamp: Allow to reset a task uclamp constraint value
  sched/core: Fix typos in comments
  Documentation: scheduler: fix information on arch SD flags, sched_domain and sched_debug
  ...

Pull RCU updates from Thomas Gleixner:
 "RCU, LKMM and KCSAN updates collected by Paul McKenney.

  RCU:
   - Avoid cpuinfo-induced IPI pileups and idle-CPU IPIs

   - Lockdep-RCU updates reducing the need for __maybe_unused

   - Tasks-RCU updates

   - Miscellaneous fixes

   - Documentation updates

   - Torture-test updates

  KCSAN:
   - updates for selftests, avoiding setting watchpoints on NULL pointers

   - fix to watchpoint encoding

  LKMM:
   - updates for documentation along with some updates to example-code
     litmus tests"

* tag 'core-rcu-2020-12-14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (72 commits)
  srcu: Take early exit on memory-allocation failure
  rcu/tree: Defer kvfree_rcu() allocation to a clean context
  rcu: Do not report strict GPs for outgoing CPUs
  rcu: Fix a typo in rcu_blocking_is_gp() header comment
  rcu: Prevent lockdep-RCU splats on lock acquisition/release
  rcu/tree: nocb: Avoid raising softirq for offloaded ready-to-execute CBs
  rcu,ftrace: Fix ftrace recursion
  rcu/tree: Make struct kernel_param_ops definitions const
  rcu/tree: Add a warning if CPU being onlined did not report QS already
  rcu: Clarify nocb kthreads naming in RCU_NOCB_CPU config
  rcu: Fix single-CPU check in rcu_blocking_is_gp()
  rcu: Implement rcu_segcblist_is_offloaded() config dependent
  list.h: Update comment to explicitly note circular lists
  rcu: Panic after fixed number of stalls
  x86/smpboot:  Move rcu_cpu_starting() earlier
  rcu: Allow rcu_irq_enter_check_tick() from NMI
  tools/memory-model: Label MP tests' producers and consumers
  tools/memory-model: Use "buf" and "flag" for message-passing tests
  tools/memory-model: Add types to litmus tests
  tools/memory-model: Add a glossary of LKMM terms
  ...

PowerPC testing encountered boot failures due to RCU Tasks not being
fully initialized until core_initcall() time.  This commit therefore
initializes RCU Tasks (along with Rude RCU and RCU Tasks Trace) just
before early_initcall() time, thus allowing waiting on RCU Tasks grace
periods from early_initcall() handlers.

Link: https://lore.kernel.org/rcu/87eekfh80a.fsf@dja-thinkpad.axtens.net/
Fixes: 36dadef23fcc ("kprobes: Init kprobes in early_initcall")
Tested-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Signed-off-by: Ingo Molnar <mingo@kernel.org>

Get rid of the __call_single_node union and clean up the API a little
to avoid external code relying on the structure layout as much.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

cpuinfo.2020.11.06a: Speedups for /proc/cpuinfo.
doc.2020.11.06a: Documentation updates.
fixes.2020.11.19b: Miscellaneous fixes.
lockdep.2020.11.02a: Lockdep-RCU updates to avoid "unused variable".
tasks.2020.11.06a: Tasks-RCU updates.
torture.2020.11.06a': Torture-test updates.

It turns out that init_srcu_struct() can be invoked from usermode tasks,
and that fatal signals received by these tasks can cause memory-allocation
failures.  These failures are not handled well by init_srcu_struct(),
so much so that NULL pointer dereferences can result.  This commit
therefore causes init_srcu_struct() to take an early exit upon detection
of memory-allocation failure.

Link: https://lore.kernel.org/lkml/20200908144306.33355-1-aik@ozlabs.ru/
Reported-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Tested-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

The current memmory-allocation interface causes the following difficulties
for kvfree_rcu():

a) If built with CONFIG_PROVE_RAW_LOCK_NESTING, the lockdep will
   complain about violation of the nesting rules, as in "BUG: Invalid
   wait context".  This Kconfig option checks for proper raw_spinlock
   vs. spinlock nesting, in particular, it is not legal to acquire a
   spinlock_t while holding a raw_spinlock_t.

   This is a problem because kfree_rcu() uses raw_spinlock_t whereas the
   "page allocator" internally deals with spinlock_t to access to its
   zones. The code also can be broken from higher level of view:
   <snip>
       raw_spin_lock(&some_lock);
       kfree_rcu(some_pointer, some_field_offset);
   <snip>

b) If built with CONFIG_PREEMPT_RT, spinlock_t is converted into
   sleeplock.  This means that invoking the page allocator from atomic
   contexts results in "BUG: scheduling while atomic".

c) Please note that call_rcu() is already invoked from raw atomic context,
   so it is only reasonable to expaect that kfree_rcu() and kvfree_rcu()
   will also be called from atomic raw context.

This commit therefore defers page allocation to a clean context using the
combination of an hrtimer and a workqueue.  The hrtimer stage is required
in order to avoid deadlocks with the scheduler.  This deferred allocation
is required only when kvfree_rcu()'s per-CPU page cache is empty.

Link: https://lore.kernel.org/lkml/20200630164543.4mdcf6zb4zfclhln@linutronix.de/
Fixes: 3042f83f19be ("rcu: Support reclaim for head-less object")
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

An outgoing CPU is marked offline in a stop-machine handler and most
of that CPU's services stop at that point, including IRQ work queues.
However, that CPU must take another pass through the scheduler and through
a number of CPU-hotplug notifiers, many of which contain RCU readers.
In the past, these readers were not a problem because the outgoing CPU
has interrupts disabled, so that rcu_read_unlock_special() would not
be invoked, and thus RCU would never attempt to queue IRQ work on the
outgoing CPU.

This changed with the advent of the CONFIG_RCU_STRICT_GRACE_PERIOD
Kconfig option, in which rcu_read_unlock_special() is invoked upon exit
from almost all RCU read-side critical sections.  Worse yet, because
interrupts are disabled, rcu_read_unlock_special() cannot immediately
report a quiescent state and will therefore attempt to defer this
reporting, for example, by queueing IRQ work.  Which fails with a splat
because the CPU is already marked as being offline.

But it turns out that there is no need to report this quiescent state
because rcu_report_dead() will do this job shortly after the outgoing
CPU makes its final dive into the idle loop.  This commit therefore
makes rcu_read_unlock_special() refrain from queuing IRQ work onto
outgoing CPUs.

Fixes: 44bad5b3cca2 ("rcu: Do full report for .need_qs for strict GPs")
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Jann Horn <jannh@google.com>