The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: 5097cbcb38e6e0d2627c9dde1985e91d2c9f880e
Gitweb: https://git.kernel.org/tip/5097cbcb38e6e0d2627c9dde1985e91d2c9f880e
Author: Oleg Nesterov <oleg@xxxxxxxxxx>
AuthorDate: Thu, 11 Apr 2024 16:39:05 +02:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Sun, 28 Apr 2024 10:07:12 +02:00
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@xxxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Reviewed-by: Phil Auld <pauld@xxxxxxxxxx>
Acked-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240411143905.GA19288@xxxxxxxxxx
Closes: https://lore.kernel.org/all/20240402105847.GA24832@xxxxxxxxxx/
---
Documentation/timers/no_hz.rst | 7 ++-----
kernel/sched/isolation.c | 11 ++++++++++-
2 files changed, 12 insertions(+), 6 deletions(-)
diff --git a/Documentation/timers/no_hz.rst b/Documentation/timers/no_hz.rst
index f8786be..7fe8ef9 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.
diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index 373d42c..2a262d3 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -46,7 +46,16 @@ int housekeeping_any_cpu(enum hk_type type)
if (cpu < nr_cpu_ids)
return cpu;
- return cpumask_any_and(housekeeping.cpumasks[type], cpu_online_mask);
+ cpu = cpumask_any_and(housekeeping.cpumasks[type], cpu_online_mask);
+ if (likely(cpu < nr_cpu_ids))
+ return cpu;
+ /*
+ * Unless we have another problem this can only happen
+ * at boot time before start_secondary() brings the 1st
+ * housekeeping CPU up.
+ */
+ WARN_ON_ONCE(system_state == SYSTEM_RUNNING ||
+ type != HK_TYPE_TIMER);
}
}
return smp_processor_id();
|