dump_backtrace may be called in kthread context, which is not bound to a single cpu, i.e. khungtaskd, then calling smp_processor_id may trigger the below bug report:
BUG: using smp_processor_id() in preemptible [00000000] code: khungtaskd/71 caller is debug_smp_processor_id+0x1c/0x28 CPU: 3 PID: 71 Comm: khungtaskd Not tainted 4.5.0-rc1 #144 Hardware name: Freescale Layerscape 2085a RDB Board (DT) Call trace: [<ffffffc00008d120>] dump_backtrace+0x0/0x290 [<ffffffc00008d3d4>] show_stack+0x24/0x30 [<ffffffc0006bfd1c>] dump_stack+0x8c/0xd8 [<ffffffc0006fe56c>] check_preemption_disabled+0x184/0x188 [<ffffffc0006fe58c>] debug_smp_processor_id+0x1c/0x28 [<ffffffc00008d1a4>] dump_backtrace+0x84/0x290 [<ffffffc00008d3d4>] show_stack+0x24/0x30 [<ffffffc00012aa5c>] sched_show_task+0x16c/0x280 [<ffffffc0001f3df8>] watchdog+0x560/0x708 [<ffffffc000111bb8>] kthread+0x1b0/0x1d0 [<ffffffc0000864d0>] ret_from_fork+0x10/0x40
Replace it to raw version to prevent from the race condition.
Signed-off-by: Yang Shi yang.shi@linaro.org --- arch/arm64/kernel/traps.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c index cbedd72..9abe236 100644 --- a/arch/arm64/kernel/traps.c +++ b/arch/arm64/kernel/traps.c @@ -146,7 +146,7 @@ static void dump_instr(const char *lvl, struct pt_regs *regs) static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk) { struct stackframe frame; - unsigned long irq_stack_ptr = IRQ_STACK_PTR(smp_processor_id()); + unsigned long irq_stack_ptr = IRQ_STACK_PTR(raw_smp_processor_id()); int skip;
pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);