The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x 07c54cc5988f19c9642fd463c2dbdac7fc52f777 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024061706-smudgy-gumball-93c0@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

07c54cc5988f ("tick/nohz_full: Don't abuse smp_call_function_single() in tick_setup_device()") f87cbcb345d0 ("timekeeping: Use READ/WRITE_ONCE() for tick_do_timer_cpu") a478ffb2ae23 ("tick: Move individual bit features to debuggable mask accesses") 3ce74f1a8566 ("tick: Move got_idle_tick away from common flags") 3ad6eb0683a1 ("tick: Start centralizing tick related CPU hotplug operations") 3650f49bfb95 ("tick/sched: Rename tick_nohz_stop_sched_tick() to tick_nohz_full_stop_tick()") 27dc08096ce4 ("tick: Use IS_ENABLED() whenever possible") 37263ba0c44b ("tick/nohz: Remove duplicate between lowres and highres handlers") ffb7e01c4e65 ("tick/nohz: Remove duplicate between tick_nohz_switch_to_nohz() and tick_setup_sched_timer()") 4c532939aa2e ("tick/sched: Split out jiffies update helper function") 73129cf4b69c ("timers: Optimization for timer_base_try_to_set_idle()") e2e1d724e948 ("timers: Move marking timer bases idle into tick_nohz_stop_tick()") 39ed699fb660 ("timers: Split out get next timer interrupt") bebed6649e85 ("timers: Restructure get_next_timer_interrupt()") f365d0550615 ("tick/sched: Add function description for tick_nohz_next_event()") da65f29dada7 ("timers: Fix nextevt calculation when no timers are pending") bb8caad5083f ("timers: Rework idle logic") 7a39a5080ef0 ("timers: Use already existing function for forwarding timer base") b5e6f59888c7 ("timers: Move store of next event into __next_timer_interrupt()") b573c73101d8 ("tracing/timers: Add tracepoint for tracking timer base is_idle flag")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 07c54cc5988f19c9642fd463c2dbdac7fc52f777 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov oleg@redhat.com Date: Tue, 28 May 2024 14:20:19 +0200 Subject: [PATCH] tick/nohz_full: Don't abuse smp_call_function_single() in tick_setup_device()

After the recent commit 5097cbcb38e6 ("sched/isolation: Prevent boot crash when the boot CPU is nohz_full") the kernel no longer crashes, but there is another problem.

In this case tick_setup_device() calls tick_take_do_timer_from_boot() to update tick_do_timer_cpu and this triggers the WARN_ON_ONCE(irqs_disabled) in smp_call_function_single().

Kill tick_take_do_timer_from_boot() and just use WRITE_ONCE(), the new comment explains why this is safe (thanks Thomas!).

Fixes: 08ae95f4fd3b ("nohz_full: Allow the boot CPU to be nohz_full") Signed-off-by: Oleg Nesterov oleg@redhat.com Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20240528122019.GA28794@redhat.com Link: https://lore.kernel.org/all/20240522151742.GA10400@redhat.com

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index d88b13076b79..a47bcf71defc 100644 --- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -178,26 +178,6 @@ void tick_setup_periodic(struct clock_event_device *dev, int broadcast) } }

-#ifdef CONFIG_NO_HZ_FULL -static void giveup_do_timer(void *info) -{ - int cpu = *(unsigned int *)info; - - WARN_ON(tick_do_timer_cpu != smp_processor_id()); - - tick_do_timer_cpu = cpu; -} - -static void tick_take_do_timer_from_boot(void) -{ - int cpu = smp_processor_id(); - int from = tick_do_timer_boot_cpu; - - if (from >= 0 && from != cpu) - smp_call_function_single(from, giveup_do_timer, &cpu, 1); -} -#endif - /* * Setup the tick device */ @@ -221,19 +201,25 @@ static void tick_setup_device(struct tick_device *td, tick_next_period = ktime_get(); #ifdef CONFIG_NO_HZ_FULL /* - * The boot CPU may be nohz_full, in which case set - * tick_do_timer_boot_cpu so the first housekeeping - * secondary that comes up will take do_timer from - * us. + * The boot CPU may be nohz_full, in which case the + * first housekeeping secondary will take do_timer() + * from it. */ if (tick_nohz_full_cpu(cpu)) tick_do_timer_boot_cpu = cpu;

- } else if (tick_do_timer_boot_cpu != -1 && - !tick_nohz_full_cpu(cpu)) { - tick_take_do_timer_from_boot(); + } else if (tick_do_timer_boot_cpu != -1 && !tick_nohz_full_cpu(cpu)) { tick_do_timer_boot_cpu = -1; - WARN_ON(READ_ONCE(tick_do_timer_cpu) != cpu); + /* + * The boot CPU will stay in periodic (NOHZ disabled) + * mode until clocksource_done_booting() called after + * smp_init() selects a high resolution clocksource and + * timekeeping_notify() kicks the NOHZ stuff alive. + * + * So this WRITE_ONCE can only race with the READ_ONCE + * check in tick_periodic() but this race is harmless. + */ + WRITE_ONCE(tick_do_timer_cpu, cpu); #endif }