sst-linux/Documentation
Oleg Nesterov ba181019d1 sched/isolation: Prevent boot crash when the boot CPU is nohz_full
Documentation/timers/no_hz.rst states that the "nohz_full=" mask must not
include the boot CPU, which is no longer true after:

  08ae95f4fd ("nohz_full: Allow the boot CPU to be nohz_full").

However after:

  aae17ebb53cd ("workqueue: Avoid using isolated cpus' timers on queue_delayed_work")

the kernel will crash at boot time in this case; housekeeping_any_cpu()
returns an invalid CPU number until smp_init() brings the first
housekeeping CPU up.

Change housekeeping_any_cpu() to check the result of cpumask_any_and() and
return smp_processor_id() in this case.

This is just the simple and backportable workaround which fixes the
symptom, but smp_processor_id() at boot time should be safe at least for
type == HK_TYPE_TIMER, this more or less matches the tick_do_timer_boot_cpu
logic.

There is no worry about cpu_down(); tick_nohz_cpu_down() will not allow to
offline tick_do_timer_cpu (the 1st online housekeeping CPU).

[ Apply only documentation changes as commit which causes boot
  crash when boot CPU is nohz_full is not backported to stable
  kernels - Krishanth ]

Reported-by: Chris von Recklinghausen <crecklin@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Phil Auld <pauld@redhat.com>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20240411143905.GA19288@redhat.com
Closes: https://lore.kernel.org/all/20240402105847.GA24832@redhat.com/
Signed-off-by: Krishanth Jagaduri <Krishanth.Jagaduri@sony.com>
[ strip out upstream commit and Fixes: so tools don't get confused that
  this commit actually does anything real - gregkh]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2025-03-28 21:58:48 +01:00
..
ABI PCI: Add 'reset_subordinate' to reset hierarchy below bridge 2024-12-14 19:54:48 +01:00
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timers sched/isolation: Prevent boot crash when the boot CPU is nohz_full 2025-03-28 21:58:48 +01:00
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