Documentation/timers/no_hz.rst | 7 ++----- kernel/sched/isolation.c | 11 ++++++++++- 2 files changed, 12 insertions(+), 6 deletions(-)
The following commit has been merged into the sched/urgent branch of tip:
Commit-ID: 8e3101b38dfc20848a23525b1e6e80bd1641d44c
Gitweb: https://git.kernel.org/tip/8e3101b38dfc20848a23525b1e6e80bd1641d44c
Author: Oleg Nesterov <oleg@redhat.com>
AuthorDate: Thu, 11 Apr 2024 16:39:05 +02:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Wed, 24 Apr 2024 21:53:34 +02:00
sched/isolation: {revent 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 commit 08ae95f4fd3b
("nohz_full: Allow the boot CPU to be nohz_full").
However after commit 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>
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/
---
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();On Wed, Apr 24, 2024 at 08:05:02PM -0000 tip-bot2 for Oleg Nesterov wrote:
> The following commit has been merged into the sched/urgent branch of tip:
>
> Commit-ID: 8e3101b38dfc20848a23525b1e6e80bd1641d44c
> Gitweb: https://git.kernel.org/tip/8e3101b38dfc20848a23525b1e6e80bd1641d44c
> Author: Oleg Nesterov <oleg@redhat.com>
> AuthorDate: Thu, 11 Apr 2024 16:39:05 +02:00
> Committer: Thomas Gleixner <tglx@linutronix.de>
> CommitterDate: Wed, 24 Apr 2024 21:53:34 +02:00
>
> sched/isolation: {revent boot crash when the boot CPU is nohz_full
>
Thanks Thomas, Typo in the reworded description :)
> Documentation/timers/no_hz.rst states that the "nohz_full=" mask must not
> include the boot CPU, which is no longer true after commit 08ae95f4fd3b
> ("nohz_full: Allow the boot CPU to be nohz_full").
>
> However after commit 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>
> 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/
> ---
> 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();
>
--
* Phil Auld <pauld@redhat.com> wrote:
> On Wed, Apr 24, 2024 at 08:05:02PM -0000 tip-bot2 for Oleg Nesterov wrote:
> > The following commit has been merged into the sched/urgent branch of tip:
> >
> > Commit-ID: 8e3101b38dfc20848a23525b1e6e80bd1641d44c
> > Gitweb: https://git.kernel.org/tip/8e3101b38dfc20848a23525b1e6e80bd1641d44c
> > Author: Oleg Nesterov <oleg@redhat.com>
> > AuthorDate: Thu, 11 Apr 2024 16:39:05 +02:00
> > Committer: Thomas Gleixner <tglx@linutronix.de>
> > CommitterDate: Wed, 24 Apr 2024 21:53:34 +02:00
> >
> > sched/isolation: {revent boot crash when the boot CPU is nohz_full
> >
>
> Thanks Thomas, Typo in the reworded description :)
Ok, so normally we wouldn't rebase just for a typo in a changelog, but
that's an annoying typo that will show up in shortlogs - so I fixed it all
up in tip:sched/urgent.
Thanks,
Ingo
On Sun, Apr 28, 2024 at 10:14:30AM +0200 Ingo Molnar wrote:
>
> * Phil Auld <pauld@redhat.com> wrote:
>
> > On Wed, Apr 24, 2024 at 08:05:02PM -0000 tip-bot2 for Oleg Nesterov wrote:
> > > The following commit has been merged into the sched/urgent branch of tip:
> > >
> > > Commit-ID: 8e3101b38dfc20848a23525b1e6e80bd1641d44c
> > > Gitweb: https://git.kernel.org/tip/8e3101b38dfc20848a23525b1e6e80bd1641d44c
> > > Author: Oleg Nesterov <oleg@redhat.com>
> > > AuthorDate: Thu, 11 Apr 2024 16:39:05 +02:00
> > > Committer: Thomas Gleixner <tglx@linutronix.de>
> > > CommitterDate: Wed, 24 Apr 2024 21:53:34 +02:00
> > >
> > > sched/isolation: {revent boot crash when the boot CPU is nohz_full
> > >
> >
> > Thanks Thomas, Typo in the reworded description :)
>
> Ok, so normally we wouldn't rebase just for a typo in a changelog, but
> that's an annoying typo that will show up in shortlogs - so I fixed it all
> up in tip:sched/urgent.
>
Yeah, I kept seeing "revert"...
Thanks,
Phil
> Thanks,
>
> Ingo
>
--
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