[PATCH] RISC-V: Enable IPI CPU Backtrace

[Björn Töpel]

takakura at valinux.co.jp writes:

> 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>

Reviewed-by: Björn Töpel <bjorn at rivosinc.com>