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authorOleg Nesterov <oleg@redhat.com>2024-04-11 17:39:05 +0300
committerIngo Molnar <mingo@kernel.org>2024-04-28 11:07:12 +0300
commit5097cbcb38e6e0d2627c9dde1985e91d2c9f880e (patch)
tree7fb2d46e50a198882d86134756797cb5ede1141e /Documentation
parent1560d1f6eb6b398bddd80c16676776c0325fe5fe (diff)
downloadlinux-5097cbcb38e6e0d2627c9dde1985e91d2c9f880e.tar.xz
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: 08ae95f4fd3b ("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). Fixes: aae17ebb53cd ("workqueue: Avoid using isolated cpus' timers on queue_delayed_work") 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/
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/timers/no_hz.rst7
1 files changed, 2 insertions, 5 deletions
diff --git a/Documentation/timers/no_hz.rst b/Documentation/timers/no_hz.rst
index f8786be15183..7fe8ef9718d8 100644
--- a/Documentation/timers/no_hz.rst
+++ b/Documentation/timers/no_hz.rst
@@ -129,11 +129,8 @@ adaptive-tick CPUs: At least one non-adaptive-tick CPU must remain
online to handle timekeeping tasks in order to ensure that system
calls like gettimeofday() returns accurate values on adaptive-tick CPUs.
(This is not an issue for CONFIG_NO_HZ_IDLE=y because there are no running
-user processes to observe slight drifts in clock rate.) Therefore, the
-boot CPU is prohibited from entering adaptive-ticks mode. Specifying a
-"nohz_full=" mask that includes the boot CPU will result in a boot-time
-error message, and the boot CPU will be removed from the mask. Note that
-this means that your system must have at least two CPUs in order for
+user processes to observe slight drifts in clock rate.) Note that this
+means that your system must have at least two CPUs in order for
CONFIG_NO_HZ_FULL=y to do anything for you.
Finally, adaptive-ticks CPUs must have their RCU callbacks offloaded.