[PATCH] RISC-V: Enable IPI CPU Backtrace

[Palmer Dabbelt]

On Tue, 16 Apr 2024 22:07:11 PDT (-0700), takakura at valinux.co.jp wrote:
> From: Ryo Takakura <takakura at valinux.co.jp>
>
> Add CPU backtrace feature using IPI on riscv.
> Currently, riscv doesn't yet support the feature while other
> architectures do. As IPI multiplexing allows to handle
> multiple IPIs, I think this feature can also be enabled
> on riscv by adding IPI.
>
> This patch defines arch_trigger_all_cpu_backtrace() which triggers
> the IPI for CPU backtrace.
> It will be triggered in the events of oops/panic when options
> (oops_all_cpu_backtrace/panic_print) are set accordingly.
>
> Below is the case of oops with the oops_all_cpu_backtrace
> enabled.
>
> $ sysctl kernel.oops_all_cpu_backtrace=1
>
> triggering oops shows:
> [  435.716754] NMI backtrace for cpu 3
> [  435.716893] CPU: 3 PID: 621 Comm: in:imklog Tainted: G           OE      6.9.0-rc4 #1
> [  435.717086] Hardware name: riscv-virtio,qemu (DT)
> [  435.717182] epc : fallback_scalar_usercopy+0x8/0xdc
> [  435.717300]  ra : _copy_to_user+0x32/0x58
> [  435.717391] epc : ffffffff80c33d88 ra : ffffffff80598e3c sp : ff20000000e83b50
> [  435.717544]  gp : ffffffff82066bf0 tp : ff60000091fd7000 t0 : 3363303866660000
> [  435.717711]  t1 : 000000000000005b t2 : 3363303866666666 s0 : ff20000000e83b60
> [  435.717874]  s1 : 00000000000001af a0 : 00007ff74d3df74f a1 : ff60000082cdc800
> [  435.718040]  a2 : 000000000000003c a3 : 0000000000000000 a4 : 0000000000000000
> [  435.718196]  a5 : 00ffffffffffffc4 a6 : 0000000000000000 a7 : 0000000000000010
> [  435.718333]  s2 : ff60000082cdc800 s3 : ffffffff82066910 s4 : 0000000000001df1
> [  435.718475]  s5 : ffffffff8206a5b8 s6 : 00007ff74d3df74f s7 : ffffffff8206a5b0
> [  435.718616]  s8 : ff60000082cdc800 s9 : ffffffff81e26208 s10: 000000000000003c
> [  435.718760]  s11: ffffffff8206a5ad t3 : ff60000082cdc812 t4 : ff60000082cdc812
> [  435.718909]  t5 : ff60000082cdc818 t6 : 0000000000040000
> [  435.719019] status: 0000000000040120 badaddr: 0000000000000000 cause: 8000000000000001
> [  435.719191] [<ffffffff80c33d88>] fallback_scalar_usercopy+0x8/0xdc
> [  435.719330] [<ffffffff80094eee>] syslog_print+0x1f4/0x2b2
> [  435.719446] [<ffffffff80095e10>] do_syslog.part.0+0xb0/0x326
> [  435.719594] [<ffffffff8009692e>] do_syslog+0x66/0x88
> [  435.719816] [<ffffffff803a1a80>] kmsg_read+0x44/0x5c
> [  435.720017] [<ffffffff8038ea92>] proc_reg_read+0x7a/0xa8
> [  435.720251] [<ffffffff802fae20>] vfs_read+0x94/0x264
> [  435.720478] [<ffffffff802fb906>] ksys_read+0x64/0xe4
> [  435.720709] [<ffffffff802fb9a6>] __riscv_sys_read+0x20/0x2c
> [  435.720880] [<ffffffff80c43ea2>] do_trap_ecall_u+0x60/0x1d4
> [  435.721236] [<ffffffff80c4f74c>] ret_from_exception+0x0/0x64
>
> Signed-off-by: Ryo Takakura <takakura at valinux.co.jp>
> ---
>  arch/riscv/include/asm/irq.h |  3 +++
>  arch/riscv/kernel/smp.c      | 16 ++++++++++++++++
>  2 files changed, 19 insertions(+)
>
> diff --git a/arch/riscv/include/asm/irq.h b/arch/riscv/include/asm/irq.h
> index 8e10a94430a2..ed8f76879270 100644
> --- a/arch/riscv/include/asm/irq.h
> +++ b/arch/riscv/include/asm/irq.h
> @@ -12,6 +12,9 @@
>
>  #include <asm-generic/irq.h>
>
> +void arch_trigger_cpumask_backtrace(const cpumask_t *mask, int exclude_cpu);
> +#define arch_trigger_cpumask_backtrace arch_trigger_cpumask_backtrace

I'm getting a build failure with SMP=n (allnoconfig), the implementation 
is in smp.c which isn't built without SMP.

> +
>  void riscv_set_intc_hwnode_fn(struct fwnode_handle *(*fn)(void));
>
>  struct fwnode_handle *riscv_get_intc_hwnode(void);
> diff --git a/arch/riscv/kernel/smp.c b/arch/riscv/kernel/smp.c
> index 45dd4035416e..6e297b9eb641 100644
> --- a/arch/riscv/kernel/smp.c
> +++ b/arch/riscv/kernel/smp.c
> @@ -21,6 +21,7 @@
>  #include <linux/delay.h>
>  #include <linux/irq.h>
>  #include <linux/irq_work.h>
> +#include <linux/nmi.h>
>
>  #include <asm/tlbflush.h>
>  #include <asm/cacheflush.h>
> @@ -33,6 +34,7 @@ enum ipi_message_type {
>  	IPI_CPU_CRASH_STOP,
>  	IPI_IRQ_WORK,
>  	IPI_TIMER,
> +	IPI_CPU_BACKTRACE,
>  	IPI_MAX
>  };
>
> @@ -136,6 +138,9 @@ static irqreturn_t handle_IPI(int irq, void *data)
>  		tick_receive_broadcast();
>  		break;
>  #endif
> +	case IPI_CPU_BACKTRACE:
> +		nmi_cpu_backtrace(get_irq_regs());
> +		break;
>  	default:
>  		pr_warn("CPU%d: unhandled IPI%d\n", smp_processor_id(), ipi);
>  		break;
> @@ -212,6 +217,7 @@ static const char * const ipi_names[] = {
>  	[IPI_CPU_CRASH_STOP]	= "CPU stop (for crash dump) interrupts",
>  	[IPI_IRQ_WORK]		= "IRQ work interrupts",
>  	[IPI_TIMER]		= "Timer broadcast interrupts",
> +	[IPI_CPU_BACKTRACE]     = "CPU backtrace interrupts",
>  };
>
>  void show_ipi_stats(struct seq_file *p, int prec)
> @@ -332,3 +338,13 @@ void arch_smp_send_reschedule(int cpu)
>  	send_ipi_single(cpu, IPI_RESCHEDULE);
>  }
>  EXPORT_SYMBOL_GPL(arch_smp_send_reschedule);
> +
> +static void riscv_backtrace_ipi(cpumask_t *mask)
> +{
> +	send_ipi_mask(mask, IPI_CPU_BACKTRACE);
> +}
> +
> +void arch_trigger_cpumask_backtrace(const cpumask_t *mask, int exclude_cpu)
> +{
> +	nmi_trigger_cpumask_backtrace(mask, exclude_cpu, riscv_backtrace_ipi);
> +}