Hi Liam,
On Fri, Sep 15, 2023 at 7:45 PM Liam R. Howlett Liam.Howlett@oracle.com 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/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
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 geert+renesas@glider.be
Gr{oetje,eeting}s,
Geert