linux-kernel - [PATCH] arm64: kexec: flush log to console in nmi

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Message-Id: <20210617125023.7288-1-shijie@os.amperecomputing.com>
Date:   Thu, 17 Jun 2021 12:50:23 +0000
From:   Huang Shijie <shijie@...amperecomputing.com>
To:     catalin.marinas@....com
Cc:     will@...nel.org, tabba@...gle.com, ardb@...nel.org,
        mark.rutland@....com, pasha.tatashin@...een.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        patches@...erecomputing.com, zwang@...erecomputing.com,
        Huang Shijie <shijie@...amperecomputing.com>
Subject: [PATCH] arm64: kexec: flush log to console in nmi_panic()

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

But in NMI context, the log is put in PER-CPU nmi_print_seq.
So we can not see any log on the console since we entered the NMI context,
such as the "Bye!" in previous line.

This patch fixes this issue by two steps:
	1) Uses printk_safe_flush_on_panic() to flush the log from
             nmi_print_seq to global printk ring buffer,
        2) Then uses console_flush_on_panic() to flush to console.

After this patch, we can see the "Bye!" log in the panic console.

Signed-off-by: Huang Shijie <shijie@...amperecomputing.com>
---
 arch/arm64/kernel/machine_kexec.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
index 213d56c14f60..0ab841dab9db 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>
@@ -189,6 +190,12 @@ void machine_kexec(struct kimage *kimage)
 
 	pr_info("Bye!\n");
 
+	if (in_nmi()) {
+		/* Flush the log to console if we are in NMI context */
+		printk_safe_flush_on_panic();
+		console_flush_on_panic(CONSOLE_FLUSH_PENDING);
+	}
+
 	local_daif_mask();
 
 	/*
-- 
2.30.2