Re: [RESEND PATCH] arm64: kgdb: fix single stepping

From: Jason Wessel
Date: Mon Sep 19 2016 - 18:30:24 EST

On 09/15/2016 11:32 PM, AKASHI Takahiro wrote:
@@ -176,18 +183,14 @@ int kgdb_arch_handle_exception(int exception_vector, int signo,
* over and over again.
kgdb_arch_update_addr(linux_regs, remcom_in_buffer);
- atomic_set(&kgdb_cpu_doing_single_step, -1);
- kgdb_single_step = 0;

This is a subtle change, but I assume it is what you intended? All the CPUs will get released into the run state when exiting the kgdb exception handler.
You are talking about "- kgdb_single_step = 0." Right?


Do you think that there is any (negative) side effect of this change?

Not at all. The kernel debugger always skids to a stop, and it is more reliable from a locking perspective if the other CPU threads are released while a single CPU is asked to single step until the next "skid" for all the other CPUs.

When you do not release the other CPUs you can end up single stepping a CPU which dead locks or never exits a lock elsewhere due to what ever it was blocking on never getting freed from another CPU.