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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 5f6130fa52.

Fixes: 5f6130fa52 ("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/
This commit is contained in:
Liam R. Howlett 2023-09-15 13:44:44 -04:00 committed by Peter Zijlstra
parent ce9ecca023
commit cff9b2332a
2 changed files with 2 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
kernel/sched/core.c
View File

@ -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

1
kernel/sched/idle.c
View File

@ -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)