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/[email protected]/
Link: https://lore.kernel.org/linux-mm/CAMuHMdWpvpWoDa=Ox-do92czYRvkok6_x6pYUH+ZouMcJbXy+Q@mail.gmail.com/
Fixes: 5f6130fa52ee ("tiny_rcu: Directly force QS when call_rcu_[bh|sched]() on idle_task")
Cc: [email protected]
Cc: Geert Uytterhoeven <[email protected]>
Cc: "Paul E. McKenney" <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Andreas Schwab <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Peng Zhang <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Juri Lelli <[email protected]>
Cc: Vincent Guittot <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: "Mike Rapoport (IBM)" <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Liam R. Howlett <[email protected]>
---
v1: https://lore.kernel.org/linux-mm/[email protected]/
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)
--
2.39.2
Hi Liam,
On Fri, Sep 15, 2023 at 7:45 PM Liam R. Howlett <[email protected]> wrote:
> 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/[email protected]/
> Link: https://lore.kernel.org/linux-mm/CAMuHMdWpvpWoDa=Ox-do92czYRvkok6_x6pYUH+ZouMcJbXy+Q@mail.gmail.com/
> Fixes: 5f6130fa52ee ("tiny_rcu: Directly force QS when call_rcu_[bh|sched]() on idle_task")
> Cc: [email protected]
> Cc: Geert Uytterhoeven <[email protected]>
> Cc: "Paul E. McKenney" <[email protected]>
> Cc: Christophe Leroy <[email protected]>
> Cc: Andreas Schwab <[email protected]>
> Cc: Matthew Wilcox <[email protected]>
> Cc: Peng Zhang <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Juri Lelli <[email protected]>
> Cc: Vincent Guittot <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: "Mike Rapoport (IBM)" <[email protected]>
> Cc: Vlastimil Babka <[email protected]>
> Signed-off-by: Liam R. Howlett <[email protected]>
Thanks for your patch!
This fixes the
WARNING: CPU: 0 PID: 0 at init/main.c:992 start_kernel+0x2f0/0x480
I was seeing during boot on Renesas RZ/A1 and RZ/A2 since commit
cfeb6ae8bcb96ccf ("maple_tree: disable mas_wr_append() when other
readers are possible") in v6.5.
And unlike v1, this does not cause lots of new warnings on e.g. R-Car M2-W.
Tested-by: Geert Uytterhoeven <[email protected]>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
On Fri, Sep 15, 2023 at 01:44:44PM -0400, Liam R. Howlett wrote:
> 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/[email protected]/
> Link: https://lore.kernel.org/linux-mm/CAMuHMdWpvpWoDa=Ox-do92czYRvkok6_x6pYUH+ZouMcJbXy+Q@mail.gmail.com/
> Fixes: 5f6130fa52ee ("tiny_rcu: Directly force QS when call_rcu_[bh|sched]() on idle_task")
> Signed-off-by: Liam R. Howlett <[email protected]>
> ---
Thanks!, I've queued this up for sched/urgent but will let the robots at
it before I push it out to -tip.