kernel/sched: Modify initial boot task idle setup

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.

Fixes: 5f6130fa52ee ("tiny_rcu: Directly force QS when call_rcu_[bh|sched]() on idle_task")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/linux-mm/CAMuHMdWpvpWoDa=Ox-do92czYRvkok6_x6pYUH+ZouMcJbXy+Q@mail.gmail.com/

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2299a5cfbfb9ed250695edb75d977edbe61eaf43..802551e0009bf1ef66191441a802633bb57543bc 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9269,7 +9269,7 @@ 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 342f58a329f528fcc6060208cfba9b7e908d3a98..5007b25c5bc653a9ca0696af1f7136150cd6131e 100644 (file)
--- 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)