Initial booting is setting the task flag to idle (PF_IDLE) by the call path sched_init() -> init_idle(). Having the task idle and calling call_rcu() in kernel/rcu/tiny.c means that TIF_NEED_RESCHED will be set. Subsequent calls to any cond_resched() will enable IRQs, potentially earlier than the IRQ setup has completed. Recent changes have caused just this scenario and IRQs have been enabled early.

This causes a warning later in start_kernel() as interrupts are enabled before they are fully set up.

Fix this issue by setting the PF_IDLE flag later in the boot sequence.

Although the boot task was marked as idle since (at least) d80e4fda576d, I am not sure that it is wrong to do so. The forced context-switch on idle task was introduced in the tiny_rcu update, so I'm going to claim this fixes 5f6130fa52ee.

Link: https://lore.kernel.org/linux-mm/87v8cv22jh.fsf@mail.lhotse/ Link: https://lore.kernel.org/linux-mm/CAMuHMdWpvpWoDa=Ox-do92czYRvkok6_x6pYUH+Zou... Fixes: 5f6130fa52ee ("tiny_rcu: Directly force QS when call_rcu_[bh|sched]() on idle_task") Cc: stable@vger.kernel.org Cc: Geert Uytterhoeven geert@linux-m68k.org Cc: "Paul E. McKenney" paulmck@kernel.org Cc: Christophe Leroy christophe.leroy@csgroup.eu Cc: Andreas Schwab schwab@linux-m68k.org Cc: Matthew Wilcox willy@infradead.org Cc: Peng Zhang zhangpeng.00@bytedance.com Cc: Peter Zijlstra peterz@infradead.org Cc: Ingo Molnar mingo@redhat.com Cc: Juri Lelli juri.lelli@redhat.com Cc: Vincent Guittot vincent.guittot@linaro.org Cc: Andrew Morton akpm@linux-foundation.org Cc: "Mike Rapoport (IBM)" rppt@kernel.org Cc: Vlastimil Babka vbabka@suse.cz Signed-off-by: Liam R. Howlett Liam.Howlett@oracle.com ---

v1: https://lore.kernel.org/linux-mm/20230913005647.1534747-1-Liam.Howlett@oracl...

kernel/sched/core.c | 2 +- kernel/sched/idle.c | 1 + 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c index c52c2eba7c73..e8f73ff12126 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -9271,7 +9271,7 @@ void __init init_idle(struct task_struct *idle, int cpu) * PF_KTHREAD should already be set at this point; regardless, make it * look like a proper per-CPU kthread. */ - idle->flags |= PF_IDLE | PF_KTHREAD | PF_NO_SETAFFINITY; + idle->flags |= PF_KTHREAD | PF_NO_SETAFFINITY; kthread_set_per_cpu(idle, cpu);

#ifdef CONFIG_SMP diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 342f58a329f5..5007b25c5bc6 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -373,6 +373,7 @@ EXPORT_SYMBOL_GPL(play_idle_precise);

void cpu_startup_entry(enum cpuhp_state state) { + current->flags |= PF_IDLE; arch_cpu_idle_prepare(); cpuhp_online_idle(state); while (1)