Hi Liam, On Fri, Sep 15, 2023 at 7:45 PM Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> 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+ZouMcJbXy+Q@xxxxxxxxxxxxxx/ > Fixes: 5f6130fa52ee ("tiny_rcu: Directly force QS when call_rcu_[bh|sched]() on idle_task") > Cc: stable@xxxxxxxxxxxxxxx > Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> > Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx> > Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx> > Cc: Andreas Schwab <schwab@xxxxxxxxxxxxxx> > Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> > Cc: Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: Juri Lelli <juri.lelli@xxxxxxxxxx> > Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: "Mike Rapoport (IBM)" <rppt@xxxxxxxxxx> > Cc: Vlastimil Babka <vbabka@xxxxxxx> > Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> 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@xxxxxxxxx> Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx 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
