linux-kernel - [PATCH] kexec: dump kmessage before machine

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Date:   Fri,  5 Jun 2020 15:46:42 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     pasha.tatashin@...een.com, jmorris@...ei.org, sashal@...nel.org,
        pmladek@...e.com, ebiederm@...ssion.com, keescook@...omium.org,
        anton@...msg.org, ccross@...roid.com, tony.luck@...el.com,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] kexec: dump kmessage before machine_kexec

kmsg_dump(KMSG_DUMP_SHUTDOWN) is called before
machine_restart(), machine_halt(), machine_power_off(), the only one that
is missing is  machine_kexec().

The dmesg output that it contains can be used to study the shutdown
performance of both kernel and systemd during kexec reboot.

Here is example of dmesg data collected after kexec:

root@...at-cp22:~# cat /sys/fs/pstore/dmesg-ramoops-0 | tail
...
<6>[   70.914592] psci: CPU3 killed (polled 0 ms)
<5>[   70.915705] CPU4: shutdown
<6>[   70.916643] psci: CPU4 killed (polled 4 ms)
<5>[   70.917715] CPU5: shutdown
<6>[   70.918725] psci: CPU5 killed (polled 0 ms)
<5>[   70.919704] CPU6: shutdown
<6>[   70.920726] psci: CPU6 killed (polled 4 ms)
<5>[   70.921642] CPU7: shutdown
<6>[   70.922650] psci: CPU7 killed (polled 0 ms)

Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
---
 kernel/kexec_core.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index c19c0dad1ebe..50027f759a97 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -37,6 +37,7 @@
 #include <linux/compiler.h>
 #include <linux/hugetlb.h>
 #include <linux/frame.h>
+#include <linux/kmsg_dump.h>
 
 #include <asm/page.h>
 #include <asm/sections.h>
@@ -1181,6 +1182,7 @@ int kernel_kexec(void)
 		machine_shutdown();
 	}
 
+	kmsg_dump(KMSG_DUMP_SHUTDOWN);
 	machine_kexec(kexec_image);
 
 #ifdef CONFIG_KEXEC_JUMP
-- 
2.25.1