[PATCH v4 2/2] arm64: show signal info for global init

[qiwu.chen]

Currently, it's hard to debug panic issues caused by kill init
on arm64, since there is no debug info from user mode in current
panic msg such as the user_regs and maps info.

This patch shows signal info sent to the global init, which will
be helpful for debugging kill init issue caused by unhandled exception
from user mode.

- changes history:
v3:
https://lore.kernel.org/all/20240922095504.7182-1-qiwu.chen@transsion.com/
https://lore.kernel.org/all/20240922095504.7182-2-qiwu.chen@transsion.com/
v2: https://lore.kernel.org/all/20231110031553.33186-1-qiwu.chen@transsion.com/
v1: https://lore.kernel.org/all/20231110022720.GA3087@rlk/

Signed-off-by: qiwu.chen <qiwu.chen at transsion.com>
---
 arch/arm64/kernel/traps.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 563cbce11126..3150fb84195f 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -247,12 +247,20 @@ static void arm64_show_signal(int signo, const char *str)
 	unsigned long esr = tsk->thread.fault_code;
 	struct pt_regs *regs = task_pt_regs(tsk);
 
+	/*
+	 * The signal sent to the global init needs to be shown,
+	 * which is useful for debugging kill init issue.
+	 */
+	if (unlikely(is_global_init(tsk)))
+		goto dump;
+
 	/* Leave if the signal won't be shown */
 	if (!show_unhandled_signals ||
 	    !unhandled_signal(tsk, signo) ||
 	    !__ratelimit(&rs))
 		return;
 
+dump:
 	pr_info("%s[%d]: unhandled exception: ", tsk->comm, task_pid_nr(tsk));
 	if (esr)
 		pr_cont("%s, ESR 0x%016lx, ", esr_get_class_string(esr), esr);
-- 
2.25.1