Re: [PATCH] risc-v: Fix order of IPI enablement vs RCU startup

Palmer Dabbelt
2023-07-03T18:45:50Z

On Mon, 03 Jul 2023 11:31:26 PDT (-0700), Marc Zyngier wrote:
> Conor reports that risc-v tries to enable IPIs before telling the
> core code to enable RCU. With the introduction of the mapple tree
> as a backing store for the irq descriptors, this results in
> a very shouty boot sequence, as RCU is legitimately upset.
>
> Restore some sanity by moving the risc_ipi_enable() call after
> notify_cpu_starting(), which explicitly enables RCU on the calling
> CPU.
>
> Fixes: 832f15f42646 ("RISC-V: Treat IPIs as normal Linux IRQs")
> Reported-by: Conor Dooley <conor@kernel.org>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> Link: https://lore.kernel.org/r/20230703-dupe-frying-79ae2ccf94eb@spud
> Cc: Anup Patel <apatel@ventanamicro.com>
> Cc: Palmer Dabbelt <palmer@rivosinc.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> ---
> arch/riscv/kernel/smpboot.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> index bb0b76e1a6d4..f4d6acb38dd0 100644
> --- a/arch/riscv/kernel/smpboot.c
> +++ b/arch/riscv/kernel/smpboot.c
> @@ -238,10 +238,11 @@ asmlinkage __visible void smp_callin(void)
> mmgrab(mm);
> current->active_mm = mm;
>
> - riscv_ipi_enable();
> -
> store_cpu_topology(curr_cpuid);
> notify_cpu_starting(curr_cpuid);
> +
> + riscv_ipi_enable();
> +
> numa_add_cpu(curr_cpuid);
> set_cpu_online(curr_cpuid, 1);
> probe_vendor_features(curr_cpuid);

Thanks. I was going to send another PR this week anyway, I can just
pick this up if you want? Either way I'll look, I've still got a few
hiccups from trying to clean up my staging bits post-merge but hopefully
it's not too bad...