This is a note to let you know that I've just added the patch titled
timers: Tag (hr)timer softirq as hotplug safe
to the 6.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
timers-tag-hr-timer-softirq-as-hotplug-safe.patch
and it can be found in the queue-6.5 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 1a6a464774947920dcedcf7409be62495c7cedd0 Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <frederic@xxxxxxxxxx>
Date: Tue, 12 Sep 2023 12:44:06 +0200
Subject: timers: Tag (hr)timer softirq as hotplug safe
From: Frederic Weisbecker <frederic@xxxxxxxxxx>
commit 1a6a464774947920dcedcf7409be62495c7cedd0 upstream.
Specific stress involving frequent CPU-hotplug operations, such as
running rcutorture for example, may trigger the following message:
NOHZ tick-stop error: local softirq work is pending, handler #02!!!"
This happens in the CPU-down hotplug process, after
CPUHP_AP_SMPBOOT_THREADS whose teardown callback parks ksoftirqd, and
before the target CPU shuts down through CPUHP_AP_IDLE_DEAD. In this
fragile intermediate state, softirqs waiting for threaded handling may be
forever ignored and eventually reported by the idle task as in the above
example.
However some vectors are known to be safe as long as the corresponding
subsystems have teardown callbacks handling the migration of their
events. The above error message reports pending timers softirq although
this vector can be considered as hotplug safe because the
CPUHP_TIMERS_PREPARE teardown callback performs the necessary migration
of timers after the death of the CPU. Hrtimers also have a similar
hotplug handling.
Therefore this error message, as far as (hr-)timers are concerned, can
be considered spurious and the relevant softirq vectors can be marked as
hotplug safe.
Fixes: 0345691b24c0 ("tick/rcu: Stop allowing RCU_SOFTIRQ in idle")
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20230912104406.312185-6-frederic@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/linux/interrupt.h | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -569,8 +569,12 @@ enum
* 2) rcu_report_dead() reports the final quiescent states.
*
* _ IRQ_POLL: irq_poll_cpu_dead() migrates the queue
+ *
+ * _ (HR)TIMER_SOFTIRQ: (hr)timers_dead_cpu() migrates the queue
*/
-#define SOFTIRQ_HOTPLUG_SAFE_MASK (BIT(RCU_SOFTIRQ) | BIT(IRQ_POLL_SOFTIRQ))
+#define SOFTIRQ_HOTPLUG_SAFE_MASK (BIT(TIMER_SOFTIRQ) | BIT(IRQ_POLL_SOFTIRQ) |\
+ BIT(HRTIMER_SOFTIRQ) | BIT(RCU_SOFTIRQ))
+
/* map softirq index to softirq name. update 'softirq_to_name' in
* kernel/softirq.c when adding a new softirq.
Patches currently in stable-queue which might be from frederic@xxxxxxxxxx are
queue-6.5/timers-tag-hr-timer-softirq-as-hotplug-safe.patch
