[PATCH v2] arm64: kexec: flush log to console in NMI context

[Huang Shijie]

If kdump is configured, nmi_panic() may run to machine_kexec().

In NMI context, the defer_console_output() defers the console
output by using wake_up_klogd to flush the printk ringbuffer
to console.

But in the machine_kexec, the system will reset, and there is
no chance for the wake_up_klogd to do its job. So we can _not_
see any log on the console since the nmi_panic
(nmi_panic() will disable the irq).

This patch fixes this issue by using console_flush_on_panic()
to flush to console.

After this patch, we can see all the log since the nmi_panic
in the panic console.

Tested-by: Adam Li <adam.li@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Huang Shijie <shijie@xxxxxxxxxxxxxxxxxxxxxx>
---
v1 --> v2:
	update this patch since the printk system is changed.

	v1:https://lkml.iu.edu/hypermail/linux/kernel/2106.2/01703.html
---
 arch/arm64/kernel/machine_kexec.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
index e16b248699d5..e961464a881e 100644
--- a/arch/arm64/kernel/machine_kexec.c
+++ b/arch/arm64/kernel/machine_kexec.c
@@ -6,6 +6,7 @@
  * Copyright (C) Huawei Futurewei Technologies.
  */
 
+#include <linux/console.h>
 #include <linux/interrupt.h>
 #include <linux/irq.h>
 #include <linux/kernel.h>
@@ -188,6 +189,8 @@ void machine_kexec(struct kimage *kimage)
 		"Some CPUs may be stale, kdump will be unreliable.\n");
 
 	pr_info("Bye!\n");
+	if (in_nmi())
+		console_flush_on_panic(CONSOLE_FLUSH_PENDING);
 
 	local_daif_mask();
 
-- 
2.30.2