When governors used during cpuidle try to find the most optimal idle state
for a CPU or a group of CPUs, they are known to quite often fail. One
reason for this is, that they are not taking into account whether there has
been an IPI scheduled for any of the CPUs that are affected by the selected
idle state.

To enable pending IPIs to be taken into account for cpuidle decisions,
introduce a new helper function, cpus_peek_for_pending_ipi().

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

The smp_call_function_many() kerneldoc comment got out of sync with the
function definition (bool parameter "wait" is incorrectly described as a
bitmask in it), so fix it up by copying the "wait" description from the
smp_call_function() kerneldoc and add information regarding the handling
of the local CPU to it.

Fixes: 49b3bd213a9f ("smp: Fix all kernel-doc warnings")
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

"boolean" is spelt as "blooean". Fix that.

Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250722161818.6139-1-romank@linux.microsoft.com

Pull stop-machine documentation updates from Paul McKenney:

 - Improve kernel-doc function-header comments

 - Document preemption and stop_machine() mutual exclusion (Joel
   Fernandes)

* tag 'stop-machine.2025.07.23a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu:
  smp: Document preemption and stop_machine() mutual exclusion
  stop_machine: Improve kernel-doc function-header comments

Recently while revising RCU's cpu online checks, there was some discussion
around how IPIs synchronize with hotplug.

Add comments explaining how preemption disable creates mutual exclusion with
CPU hotplug's stop_machine mechanism. The key insight is that stop_machine()
atomically updates CPU masks and flushes IPIs with interrupts disabled, and
cannot proceed while any CPU (including the IPI sender) has preemption
disabled.

[ Apply peterz feedback. ]

Cc: Andrea Righi <arighi@nvidia.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: rcu@vger.kernel.org
Acked-by: Paul E. McKenney <paulmck@kernel.org>
Co-developed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Whenever work is enqueued for a remote CPU, smp_call_function_many_cond()
may need to wait for that work to be completed. However, if no work is
enqueued for a remote CPU, because the condition func() evaluated to false
for all CPUs, there is no need to wait.

Set run_remote only if work was enqueued on remote CPUs.

Document the difference between "work enqueued", and "CPU needs to be
woken up"

Suggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>
Link: https://lore.kernel.org/all/20250703203019.11331ac3@fangorn

Defer check for local execution to the actual place where it is needed,
which removes the extra local variable.

Signed-off-by: Yury Norov [NVIDIA] <yury.norov@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250623000010.10124-5-yury.norov@gmail.com

smp_call_function_many_cond() opencodes cpumask_any_but().

Signed-off-by: Yury Norov [NVIDIA] <yury.norov@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250623000010.10124-3-yury.norov@gmail.com

smp_call_function_any() tries to make a local call as it's the cheapest
option, or switches to a CPU in the same node. If it's not possible, the
algorithm gives up and searches for any CPU, in a numerical order.

Instead, it can search for the best CPU based on NUMA locality, including
the 2nd nearest hop (a set of equidistant nodes), and higher.

sched_numa_find_nth_cpu() does exactly that, and also helps to drop most
of the housekeeping code.

Signed-off-by: Yury Norov [NVIDIA] <yury.norov@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250623000010.10124-2-yury.norov@gmail.com

Pull CSD-lock update from Paul McKenney:
 "Allow runtime modification of the csd_lock_timeout and
  panic_on_ipistall module parameters"

* tag 'csd-lock.2025.01.28a' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu:
  locking/csd-lock: make CSD lock debug tunables writable in /sys