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Commit 769f2099 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Greg Kroah-Hartman
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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:

  08ae95f4 ("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: default avatarChris von Recklinghausen <crecklin@redhat.com>
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarPhil Auld <pauld@redhat.com>
Acked-by: default avatarFrederic 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: default avatarKrishanth 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: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 9f89d4ad
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