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| author | Oleg Nesterov <oleg@redhat.com> | 2024-04-11 16:39:05 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-04-10 14:30:48 +0200 |
| commit | 99dd8bfdc0e0280ba4df62161e3edaab65a79102 (patch) | |
| tree | ebc8a0fb8c1bd18f682dd875b9bc589e27a1e0df /Documentation | |
| parent | 9c096d9aefcf8c6df856d1764849cd1840933a06 (diff) | |
| download | linux-99dd8bfdc0e0280ba4df62161e3edaab65a79102.tar.gz linux-99dd8bfdc0e0280ba4df62161e3edaab65a79102.tar.bz2 linux-99dd8bfdc0e0280ba4df62161e3edaab65a79102.zip | |
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).
[ 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>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/timers/no_hz.rst | 7 |
1 files changed, 2 insertions, 5 deletions
diff --git a/Documentation/timers/no_hz.rst b/Documentation/timers/no_hz.rst index c4c70e1aada3..f136f1b057d5 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. |