From: Xianting Tian xianting.tian@linux.alibaba.com
commit ad943893d5f1d0aeea892bf7b781cf8062b36d58 upstream.
Current task of executing crash kexec will be schedule out when panic is triggered by RCU Stall, as it needs to wait rcu completion. It lead to inability to enter the crash system.
The implementation of machine_crash_shutdown() is non-standard for RISC-V according to other Arch's implementation(eg, x86, arm64), we need to send IPI to stop secondary harts.
[224521.877268] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: [224521.883471] rcu: 0-...0: (3 GPs behind) idle=cfa/0/0x1 softirq=3968793/3968793 fqs=2495 [224521.891742] (detected by 2, t=5255 jiffies, g=60855593, q=328) [224521.897754] Task dump for CPU 0: [224521.901074] task:swapper/0 state:R running task stack: 0 pid: 0 ppid: 0 flags:0x00000008 [224521.911090] Call Trace: [224521.913638] [<ffffffe000c432de>] __schedule+0x208/0x5ea [224521.918957] Kernel panic - not syncing: RCU Stall [224521.923773] bad: scheduling from the idle thread! [224521.928571] CPU: 2 PID: 0 Comm: swapper/2 Kdump: loaded Tainted: G O 5.10.113-yocto-standard #1 [224521.938658] Call Trace: [224521.941200] [<ffffffe00020395c>] walk_stackframe+0x0/0xaa [224521.946689] [<ffffffe000c34f8e>] show_stack+0x32/0x3e [224521.951830] [<ffffffe000c39020>] dump_stack_lvl+0x7e/0xa2 [224521.957317] [<ffffffe000c39058>] dump_stack+0x14/0x1c [224521.962459] [<ffffffe000243884>] dequeue_task_idle+0x2c/0x40 [224521.968207] [<ffffffe000c434f4>] __schedule+0x41e/0x5ea [224521.973520] [<ffffffe000c43826>] schedule+0x34/0xe4 [224521.978487] [<ffffffe000c46cae>] schedule_timeout+0xc6/0x170 [224521.984234] [<ffffffe000c4491e>] wait_for_completion+0x98/0xf2 [224521.990157] [<ffffffe00026d9e2>] __wait_rcu_gp+0x148/0x14a [224521.995733] [<ffffffe0002761c4>] synchronize_rcu+0x5c/0x66 [224522.001307] [<ffffffe00026f1a6>] rcu_sync_enter+0x54/0xe6 [224522.006795] [<ffffffe00025a436>] percpu_down_write+0x32/0x11c [224522.012629] [<ffffffe000c4266a>] _cpu_down+0x92/0x21a [224522.017771] [<ffffffe000219a0a>] smp_shutdown_nonboot_cpus+0x90/0x118 [224522.024299] [<ffffffe00020701e>] machine_crash_shutdown+0x30/0x4a [224522.030483] [<ffffffe00029a3f8>] __crash_kexec+0x62/0xa6 [224522.035884] [<ffffffe000c3515e>] panic+0xfa/0x2b6 [224522.040678] [<ffffffe0002772be>] rcu_sched_clock_irq+0xc26/0xcb8 [224522.046774] [<ffffffe00027fc7a>] update_process_times+0x62/0x8a [224522.052785] [<ffffffe00028d522>] tick_sched_timer+0x9e/0x102 [224522.058533] [<ffffffe000280c3a>] __hrtimer_run_queues+0x16a/0x318 [224522.064716] [<ffffffe0002812ec>] hrtimer_interrupt+0xd4/0x228 [224522.070551] [<ffffffe0009a69b6>] riscv_timer_interrupt+0x3c/0x48 [224522.076646] [<ffffffe000268f8c>] handle_percpu_devid_irq+0xb0/0x24c [224522.083004] [<ffffffe00026428e>] __handle_domain_irq+0xa8/0x122 [224522.089014] [<ffffffe00062f954>] riscv_intc_irq+0x38/0x60 [224522.094501] [<ffffffe000201bd4>] ret_from_exception+0x0/0xc [224522.100161] [<ffffffe000c42146>] rcu_eqs_enter.constprop.0+0x8c/0xb8
With the patch, it can enter crash system when RCU Stall occur.
Fixes: e53d28180d4d ("RISC-V: Add kdump support") Signed-off-by: Xianting Tian xianting.tian@linux.alibaba.com Link: https://lore.kernel.org/r/20220811074150.3020189-4-xianting.tian@linux.aliba... Cc: stable@vger.kernel.org Signed-off-by: Palmer Dabbelt palmer@rivosinc.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/riscv/kernel/machine_kexec.c | 26 ++++++++++++++++++++++---- 1 file changed, 22 insertions(+), 4 deletions(-)
--- a/arch/riscv/kernel/machine_kexec.c +++ b/arch/riscv/kernel/machine_kexec.c @@ -138,19 +138,37 @@ void machine_shutdown(void) #endif }
+/* Override the weak function in kernel/panic.c */ +void crash_smp_send_stop(void) +{ + static int cpus_stopped; + + /* + * This function can be called twice in panic path, but obviously + * we execute this only once. + */ + if (cpus_stopped) + return; + + smp_send_stop(); + cpus_stopped = 1; +} + /* * machine_crash_shutdown - Prepare to kexec after a kernel crash * * This function is called by crash_kexec just before machine_kexec - * below and its goal is similar to machine_shutdown, but in case of - * a kernel crash. Since we don't handle such cases yet, this function - * is empty. + * and its goal is to shutdown non-crashing cpus and save registers. */ void machine_crash_shutdown(struct pt_regs *regs) { + local_irq_disable(); + + /* shutdown non-crashing cpus */ + crash_smp_send_stop(); + crash_save_cpu(regs, smp_processor_id()); - machine_shutdown(); pr_info("Starting crashdump kernel...\n"); }