Re: [PATCH AUTOSEL 6.6 36/47] mips/smp: Call rcutree_report_cpu_starting() earlier

[Huacai Chen]

Hi, Sasha,

The same with the LoongArch version, rcutree_report_cpu_starting()
only exists since 6.7.

Huacai

On Mon, Dec 11, 2023 at 9:53 PM Sasha Levin <sashal@xxxxxxxxxx> wrote:
>
> From: Stefan Wiehler <stefan.wiehler@xxxxxxxxx>
>
> [ Upstream commit 55702ec9603ebeffb15e6f7b113623fe1d8872f4 ]
>
> rcutree_report_cpu_starting() must be called before
> clockevents_register_device() to avoid the following lockdep splat triggered by
> calling list_add() when CONFIG_PROVE_RCU_LIST=y:
>
>   WARNING: suspicious RCU usage
>   ...
>   -----------------------------
>   kernel/locking/lockdep.c:3680 RCU-list traversed in non-reader section!!
>
>   other info that might help us debug this:
>
>   RCU used illegally from offline CPU!
>   rcu_scheduler_active = 1, debug_locks = 1
>   no locks held by swapper/1/0.
>   ...
>   Call Trace:
>   [<ffffffff8012a434>] show_stack+0x64/0x158
>   [<ffffffff80a93d98>] dump_stack_lvl+0x90/0xc4
>   [<ffffffff801c9e9c>] __lock_acquire+0x1404/0x2940
>   [<ffffffff801cbf3c>] lock_acquire+0x14c/0x448
>   [<ffffffff80aa4260>] _raw_spin_lock_irqsave+0x50/0x88
>   [<ffffffff8021e0c8>] clockevents_register_device+0x60/0x1e8
>   [<ffffffff80130ff0>] r4k_clockevent_init+0x220/0x3a0
>   [<ffffffff801339d0>] start_secondary+0x50/0x3b8
>
> raw_smp_processor_id() is required in order to avoid calling into lockdep
> before RCU has declared the CPU to be watched for readers.
>
> See also commit 29368e093921 ("x86/smpboot:  Move rcu_cpu_starting() earlier"),
> commit de5d9dae150c ("s390/smp: move rcu_cpu_starting() earlier") and commit
> 99f070b62322 ("powerpc/smp: Call rcu_cpu_starting() earlier").
>
> Signed-off-by: Stefan Wiehler <stefan.wiehler@xxxxxxxxx>
> Reviewed-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
> Signed-off-by: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> ---
>  arch/mips/kernel/smp.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c
> index 8fbef537fb885..82e2e051b4161 100644
> --- a/arch/mips/kernel/smp.c
> +++ b/arch/mips/kernel/smp.c
> @@ -351,10 +351,11 @@ early_initcall(mips_smp_ipi_init);
>   */
>  asmlinkage void start_secondary(void)
>  {
> -       unsigned int cpu;
> +       unsigned int cpu = raw_smp_processor_id();
>
>         cpu_probe();
>         per_cpu_trap_init(false);
> +       rcutree_report_cpu_starting(cpu);
>         mips_clockevent_init();
>         mp_ops->init_secondary();
>         cpu_report();
> @@ -366,7 +367,6 @@ asmlinkage void start_secondary(void)
>          */
>
>         calibrate_delay();
> -       cpu = smp_processor_id();
>         cpu_data[cpu].udelay_val = loops_per_jiffy;
>
>         set_cpu_sibling_map(cpu);
> --
> 2.42.0
>